Bioceramics

The following sections are included:

• Acknowledgements

• Preface

• CONTENTS

Porous hydroxyapatite block(HAB) could be used as a sustainer of antibiotics or anticancer drugs because of its interlinked pore structure. HAB was mixed with an antibiotic solution and decompressed in vacuum container under from 5 to 10 in. (127 mm-254 mm) Hg/20 min. to load antibiotics into HAB-pores. Twenty-one patients with osteomyelitis including one with tuberculosis and 5 patients with infected joint replacement had been treated in combination with intravenous injection. On follow up study(from 8 to 85 months; averaged 41.5 months), all of the foci had completely healed primarily by the end of the follow-up period except a case which was used on the open tibial fracture with a plate fixation. These new methods are simple, can be performed safely to treat osteomyelitis as a one stage operation.

Treatment of bone defects caused by infection is very difficult. If no filler is used, a dead space is created and this is a disadvantage for the healing of infection. However, filling the infected bone defect with free autogenous iliac bone graft also slows the healing of infection and bone absorption often occurs. We filled infected bone defects of 10 patients (6 men and 4 women; mean age: 48.1 years) with hydroxyapatite tricalcium phosphate (HAP-TCP) from 1992 to 1997. In all patients, methicillin-resistant Staphylococcus aureus was isolated from the infected focus. Administration of appropriate antibiotics and extended resection of the infected focus were performed, and the bone defect was packed with HAP-TCP after control of the infection. Wound healing, recurrence of infection, bone union, and HAP-TCP bonding were investigated. Wound healing was obtained in all patients and recurrence of infection did not occur. Bone union and HAP-TCP bonding were also obtained in all patients, and absorption of HAP-TCP did not occur. It is important for the treatment of infected bone defects that appropriate antibiotics are administered, the infected focus is excised completely, and the bone defect is filled adequately. When the former 2 conditions were fulfilled, HAP-TCP was not absorbed and was an effective filler for bone defects.

The purpose of this paper is to report the long-term results in patients with more than 10 years follow-up after calcium hydroxyapatite ceramic (CHA) implantation for the treatment of bone tumor surgery. Fifty-five patients were implanted with CHA for bone defects after the intralesional resection of benign bone tumors. The postoperative functional recovery was obtained within first one year in all patients. The radiographic density at the CHA implant sites appeared to increase during first 2 years, thereafter gradually decrease with time. The density at 10 years or more after operation was about one half of the maximum in some patients. No adverse effects and late complications were seen in any patients. These findings suggested strongly that CHA is useful for bone substitute to fill the defects in benign bone tumors.

Radiographic findings of bone union and clinical outcome in AF using HAP was evaluated and Biomechanical study was performed to certify that our method is suitable for AF using HAP. Clinically, 33 patients with myelopathy were investigated. The status of bone union was classified into 4 grades. Grade 1 is nonunion. Grade 2 is probable nonunion. Grade 3 is probable union. Grade 4 is bone union. Surgical outcome was evaluated by Japanese Orthopaedic Association(JOA) score. In biomechanical study, two models was examined. One is Robinson method without removal of end plate. The other is our method with exposure of spongy bone. No case showed grade 1 and 2.12% cases showed grade 3 and 88% grade 4. There was 5 cases with cracks. Those showed no instability and no collapse of HAP. The average preoperative and postoperative JOA score was 11.2 and 14.9 points respectively. Recovery rate was 64%. There was breakage of HAP without sinking of HAP in Robinson method. The compressive strength of breakage of HAP in Robinson method were a half to one third of those in our method. Our method gives us satisfactory clinical outcome and radiographic results, and should be used for AF using HAP.

Since 1994, a bioactive apatite - and wollastonite-containing glass-ceramic (AW-GC) granule in combination with autogenous local bone grafts obtained after neural decompression was utilized for lumbar posterolateral fusion in thirty-five patients with low back disorders with instability. The average age at surgery was 58 years, ranging from 20 to 73. The follow-up period was from 24 to 47 months with an average of 38 months. Posterior spinal instrumentation and fibrin glue were simultaneously used in all patients. Excellent neurologic recovery was obtained and maintained in every patient. A rigid primary fusion was obtained in 34 of 35 patients (97%). Screw breakage occurred in two patients(one patient had pseudoarthrosis). Transient palsy of lateral femoral cutaneus nerve was found in three patients. No other postoperative complication was observed in any patient. The results of this surgical procedure were as excellent as those of the conventional lumbar posterolateral fusion with autogenous iliac bone were. The use of AW-GC granule with a combination of autogenous local bone grafts was beneficial for posterolateral fusion of the lumbar spine.

Autogenous bone grans are related to hight rate of post-surgical diseases. Calcium phosphate ceramics may appear as potential alternatives in spinal surgery. This study report one case of lumbar spine instability underwent to instrumented posterolateral fusion using alone rectangular blocks of hydroxyapatite without augmentation of bone grafts. Clinical and radiological assessment was performed immediately after surgery at 1,6,12,24 and 36 months post-surgery. The study was completed with DEXA and C.T. scan 3D to quantify bone mineral content and bone mineral density and to assess macroscopically a solid bony fusion. Roentgenographic views showed the improvement of posterior fusion with time. 3 years later a good spinal fusion with progressive remodeling phenomena of hydroxyapatite grafts sites is present and appear related to bone growth up to the implant. Results confirmed the important role of bioceramics in spinal surgery. New bone formation appeared at the expense of the ceramics indicating a coalescence of new bone and calcium phosphate ceramics. The blocks of hydroxyapatite provide a support for bone ingrowth that require a perfect vertebral stability and a close contact between bioceramics and host bone.

A singular case of a patient with a systemic pathology is presented and discussed evaluating the analyses to which he was subjected. The SEM observations of liver’s and kidney’s bioptic slices and their x-ray microanalyses revealed that the disease was caused by debris of dental porcelain. They were released by worn dental bridges, ingested and espelled along with feces. Debris with diameters less than 20 μm passed the bowel epithelial barrier and went into the bloody stream. Liver filtered them, and they caused a granulomatous reaction. The relativity of the biocompatibility of materials is discussed.

In 1988, Titanium sticks (Ti-6A1-4V) coated with hydroxyapatite (HA) using a high-velocity flame-spraying technique (HVFST) were developed for endodontic implants. Sixty-three patients involving 87 anchored teeth were treated between April 1989 and April 1999. The subjects of this study were 2 patients with 2 implants that had been placed for 6 years each. Regarding the removal, we were not able to extirpate only the implants due to adhesion to the bone. Therefore, we removed a mass of both the surrounding bone and implants. Histologically, in the first case, coated-HA were resisted, contacted directly with the bone. In the second case, coated-HA were completely resorbed, titanium and bone were binded. we have concluded that the difference of these findings were caused by the methods of HA coating process itself.

The purpose of the present investigation was to clinically evaluate over a 6-12 month postsurgical period changes in the healing response of human intraosseous defects treated with open flap debridement with and without Bioglass® implantation. Patients were chosen for this study if they had at least 2 sites with attachment loss of ≥ 6 mm and radiographic evidence of intraosseous defects. Clinical measurements (probing depths (PD), attachment level (AL), and gingival recession (Rec) were recorded at baseline (day of the surgery), 6 and 12 months. The test defects were implanted with bioactive glass. The other sites served as unimplanted controls. At 1 year, significantly greater (P=0.0430) mean probing depth reduction was noted in the bioactive glass group (3.42 mm) compared to the control (4.31 mm). Attachment level gain was significantly improved (P=0.0016) in the bioactive glass sites (2.96 mm) compared to the control sites (1.48 mm). There was significantly less (P=0.0190) gingival recession in the bioactive glass sites (1.36 mm) compared to the control sites (1.90 mm). In conclusion, bioactive glass showed significant improvement in clinical parameters compared to open flap debridement alone. Moreover, changes in clinical parameters (PD reduction and AL gain) recorded 6 months postsurgery remained stable at the 12-month evaluation. Changes in Rec recorded at 12 months were significantly greater (P=.0104) than the 6 month values in both treatment groups.

Bioactive Glass S53P4 (BG) is an osteoconductive allograft material used in obliterating larger bone cavities e.g. frontal sinuses. In vitro model was used to investigate the behaviour of a massive frontal sinus obliteration with BG to estimate the resorption of BG at the obliterated cavities. Two sizes of granules in sixteen separate BG amounts, weight 25 g, were tested both in simulated body fluid (SBF) and a buffer containing trishydroxymethyl aminomethane citric acid (TRIS-c.a) in standard conditions. The dissolution of silicon (Si) and phosphate was detected with current plasma atom emission spectroscopy (DCP-AES) monthly up to 6 months. The calcium phosphate (CaP)- and silica (Si)-gel -layers were studied by scanning electron microscopy (SEM) at 1,3 and 6 months. The cumulative loss of Si and P was stronger in TRIS-c.a than in SBF (p<0.0001) and it was higher with smaller than larger granules in both solutions (p<0.0001). In SBF soaked BG amounts, the CaP-layer occurred in the upper part of BG amount on the uppermost granules. In TRIS-c.a, at 3 to 6 months, CaP- layer occured on the granules in the centre and lower parts of BG amount. BG seems to be a durable filling material for frontal sinuses.

A sampling of patients submitted in the past to a restoration of their auditory functionality in the framework of a planned experimental surgery, with use of different surgical techniques and materials, was recently checked to have a follow-up not lower than 5 years. A complete series of tests on their auditory functionality has allowed the formulation of statistical data on the behaviour of the different materials adopted over time. A wide comparison of the results is critically reported. Very interesting results come from the cases where alumina prostheses, with the brim covered with biological glass AP40, were adopted.

Successful repair of fractures of the orbital and maxillary zygomatic complex has four prerequisities as through understanding of the regional anatomy; an accurate diagnosis; an unimbedded exposure, and in some cases rigid fixation of fracture with orbital for restoration of the premorbid form.

Material and methods: A retrospective case series of 50 patients with bioactive implants (BG implants) of S53P4 was carried out from 1992 to 1998 at the ENT-clinic of Turku University Central Hospital. All patients diagnosed as having complex maxillary fractures with orbital floor fractures or a large blow-out fracture. All subjects underwent a transconjunctival or subciliar approach with lateral canthotomy. After prolapsed orbital contents were elevated back into the orbit the BG implant was placed over the defect.

Results: On follow-up examinations, none of the 50 patients with BG-implants presented with any evidence of orbital dystopia or complications relating to the implant. Four patients (10%) had after surgery infraorbital nerve paresthesia and one etropium. Among the all control cases there were three cases (6%) of persistent diplopia and in one case we have removed the BG-implant three months after surgery. Postoperative computed tomographic scans showed adequate maintenance of orbital and maxillary sinus volume without and evidence of resorption of the BG implant. Four patients (10%) had persistent enophthalmos without any evidence of diplopia.

Summary: BG implants are promising and well tolerated material for the repair of orbital floor fractures. Compared to conventional methods, they carry less morbidity as no donor operation is needed.

The Authors present the clinical results of a prospective study regarding the implantation, of a new composite material, made of an inorganic component (hydroxylapatite) and an organic matrix (polycaprolactone). The clinical results are referring to a group of 42 chronic otitis media patients (22 cholesteatomas and 20 granulation tissue).

The product was obtained by an appropriate combination of the two components: the role of hydroxyapatite filler concerns the biological interaction with tissues: the ceramic filler must act as starting nuclei of new bone regeneration, while the polymer guarantees the flexibility. Biocompatibility tests of the product were carried out to determine: in vitro cytotoxicity and genotoxicity. For the clinical trials the product was manufactured in 20 × 30 mm sheets of 0.2-0.5 mm thickness, it can be easily trimmed to the anatomic requirements in the individual patient.

All patients underwent a tympanoplasty with one or more of the following otologic applications of the product: repair of atticotomy defects, total or partial reconstruction of bony ear canal wall, reinforcement of tympanic retraction pockets, trans-mastoid repair of tegmen defects.

The study evalued the preliminary results obtained with a follow-up of 2 years in terms of applicability, effects and complications.

The replacement of bone losses has always been a problem throughout the history of medicine.

The golden standard in bone grafting is an autologous fresh vascularised graft, but heterologous grafts or implants of mixture of autologous bone and biomaterials are commonly used.

In the case of the cranial theca, due to the extension of the defects and to the particular nature of the implant site, considerable limitations arise in the selection of the appropriate materials.

Today, the most followed surgical technique use implants made out polymeric biomaterials, e.g. PMMA (Poly-metyl-meta-acrilate).

The literature shows that rate of complications in patients treated with PMMA is rather high, leading in many cases to revision surgery.

The objective of the present work was to evaluate the possibility to solve this clinical problem with an innovative tecnique for reconstruction of the cranial theca areas using porous hydroxyapatite matrix.

The porous hydroxyapatite matrix shows an high degree of similarity to the bone structure: it underwent complete physico-chemical characterisation. From the experimental viewpoint it seems to be a better and innovative solution for the reconstruction of the cranial theca areas.

The alumina ceramic is well known to have good biocompatibility and high wear resistance. In a total hip replacement alumina-ceramic head is used combined with polyethylene socket. However, as to a total knee replacement alumina-ceramic component has scarcely used. We have developed new total knee prosthesis with alumina ceramic femoral component designated Bisurface knee prosthesis. Bisurface knee has been designed mainly according to the total condylar prosthesis by the cooperation of Kyoto University and Kyocera Co. Bisurface knee has a unique ball-and-socket joint in the center of the posterior portion of the ftibiofemoral articulation to improve range of motion. In our institute, 233 points were replaced with Bisurface knee fixed with bone cement since 1990 until 1994. We followed 176 joints (135 cases) from 4 to 8 years (average 5.2 years). The average of knee score improved from 47 preoperatively to 81 at follow-up time. The average of flexion angle changed from 119 to 124 degree. Five cases were operated according to infection. Three cases were revised due to instability or a breakage of the patellar peg. At six-year follow-up, the survival rate was 97%. These results showed Bisurface knee with alumina ceramic femoral component has an excellent clinical performance.

Ceramic bearing surfaces have been used over the last 25 years as a clinical solution to the polyethylene wear debris which has been attributed as the major cause of aseptic loosening in total hip arthroplasties. Research has continued over the last 15 years to transpose the technology from the hip to the knee. Monolithic ceramic knee devices have been implanted, mainly in Japan, but the problem of the femoral fixation has remained. The improvement in the polyethylene materials, coupled with the more congruent knee designs, has focused the major issue to wear particle generation as opposed to fatigue or delamination.

The focus of the Brite EuRam project “Advanced Metal to Ceramic Joining Techniques To Optimise low-friction knee prostheses” was to address the issue of fixation in conjunction with the optimum ceramic bearing surface. This was achieved by the development of a biocompatible active alloy braze for joining medical grade Y-TZP zirconia to titanium alloy. Through optimised chemistry and processing conditions a high strength active alloy braze joint was obtained that satisfied all biological and mechanical requirements.

Extensive Finite Element analysis, mechanical, fatigue, wear and compression strength testing were performed to validate the new concept.

To examine the friction and wear characteristics of ceramic materials under thin film mixed lubrication for ceramic-on-ceramic artificial hip joints, uni-directional wear tests of ceramic-on-ceramic sliding pairs lubricated with distilled water were carried out by the roller-on-flat tester. The friction and wear in the rubbing pairs of alumina of the high purity and tetragonal zirconia polycrystals (Y-TZP) were examined in the combination of the same materials and different materials. The rubbing tests under higher sliding speed of 94 mm/s showed very low friction and wear even under high contact pressure conditions, probably due to the protection by the hydrodynamic film formation. In the contrary, under slow speed of 19 mm/s, the significant adhesive wear with high friction was observed. The sliding of Y-TZP against itself exhibited the higher wear than the alumina against itself. The combinations of alumina and Y-TZP showed the intermediate wear behavior. Furthermore, it is noticed at medium speeds that some wear with removal or fracture of grains was observed particularly on the stationary specimens for alumina-on-alumina pair. The influence of operating conditions and material combinations on friction and wear behavior is discussed from the viewpoint of wear and friction maps.

The following sections are included:

• Introduction

• Methods

• Results

• Discussion

• Conclusions

• Acknowledgements

• Bibliography

‘Burst’ fracture of alumina and zirconia femoral component in hip is a phenomenon, which has been assumed to occur due to the tensile hoop stresses within the femoral head. The aim of this study was to determine the effect of material properties and taper design on the stresses developed in the ceramic femoral head using finite element analysis [FEA]. An axisymmetric 3D finite element model of a 22mm diameter femoral head and taper was generated in PATRAN and analysed using ABAQUS. The common 8/10 (10mm) and a Zimmer 6° (11.5mm) tapers were modelled. To represent manufacturing tolerances the taper contact was varied by introducing angular mismatch of ±4 minutes. The 3^rd Principal stresses (hoop) were marginally higher with a CoCrMo taper compared to a Ti6A14V taper. Taper mismatch had a significant impact on the femoral head stresses. A smaller taper (10mm) with an acuter angle almost doubled the 3^rd principal stresses. Material properties and geometry is found to effect the hoop stresses generated in the femoral head. Increased rigidity led to higher stress at the taper interface. Although the stresses calculated were below the failure criteria of the materials, in mismatched tapers the induced stresses under certain geometric conditions can possibly reach to relatively critical levels.

Fifteen patients (20 hip joints) with rheumatoid arthritis, who underwent hip arthroplasties using alumina-made bipolar endoprosthesis with or without bone graft, were evaluated clinically and roentgenographically. They were followed at least for five years (range; 5-9 ys). Average hip scores improved from 32 to 72 postoperatively. According to the roentgenographic analysis, osteolysis as well as aseptic loosening of femoral components was not observed in all of the hip joints. Although proximal migration of the outer head was seen in all of the hip joint, that was not progressive in seven out of the 20 hips. In addition, the proximal migration did not affect hip scores as well as patients’ daily function. One hip joint was revised due to the breakage of alumina inner head. Average linear wear rate of polyethylene insert was 0.07 mm/year according to the computer digital analysis. The results of the present study suggests that alumina-made bipolar endoprosthesis may be an alternative to total hip arthroplasty for rheumatoid patients because of low wear performance and less invasive surgery.

We have evaluated radiographic polyethylene wear in 322 acetabular cups with alumina ceramic femoral heads (243 patients) followed for a minimum of 5 years (60 to 186 months) after total hip arthroplasties. A mean linear wear rate of all hips was 0.033 mm per year. We divided the hips into three groups. Group I (57 hips: cemented all-polyethylene cups with 28 mm heads) had a wear rate of 0.080 mm per year. Group II (117 hips: cemented metal-backed cups with 28 or 26 mm heads) had a wear rate of 0.033 mm per year. Group III (148 hips: cementless metal-backed cups with 26 mm heads) had a wear rate of 0.015 mm per year. The wear rate in Group III was significantly lower than those in Group I and Group II. The wear rate in Group II was significantly lower than that in Group I. The wear rate was not related to gender, weight, or polyethylene thickness, but to head size, loosening, osteolysis, age, and cup abduction angle. We obtained satisfactory results and low wear rate by using alumina ceramic heads.

Change of joint surfaces against various biomaterials gives us useful information regarding hemiarthroplasty. In this paper, changes of articular surfaces against various materials including Alumina were compared histologically.

In the first experiment, a rectangular parallelepiped test pieces made of titanium alloy, Alumina and of artificial osteo-chondral composite material (AOCC) were implanted into canine femoral condyles. The last material (AOCC) is composed of Titanium Fiber Mesh (TFM) into the pores of which PVA Hydrogel were infiltrated and bonded using gelling process. Change of opposing tibial articular surfaces was observed histologically for 6 months after the operation.

In the second experiment, three kinds of test pieces made of Alumina, UHMWPE and of AOCC were implanted into canine femoral head as a partial surface replacement and histological changes of acetabular cartilage were compared for 12 months.

As results, tibial joint cartilage against AOCC remained intact 6 months postoperatively, while remarkable changes such as ulceration were found in the case of Alumina and Titanium alloy. In the second experiment, remarkable erosive changes including synovial granulomatous reaction were found only in UHMWPE group. The results of these experiments encourage a clinical use of AOCC as joint material for hemiathroplasty.

The present work describes the development and mechanical evaluation, of ceramic/metal (C/M) brazed joints to be used as biocompatible encapsulation systems. The alumina/Ag-Cu-Ti/316 stainless steel joints were produced at 850°C/40 min in a vacuum furnace. The mechanical properties of the C/M joints were previously characterised using a shear-strength test. In the present study rotating beam fatigue experiments were carried out. These tests were performed to simulate the behaviour of the joints while under physiological cyclic loading. Standard S-N curves were obtained for several applied loads. The degradation behaviour of the joints was also evaluated in corrosion tests carried out in a HBSS at 37±2°C. The produced joints were further characterised by SEM/EDS before and after the degradation experiments. The fatigue results indicate that the instrumented implants will be able to work for 94 to 200 days under the typical mechanical solicitation of a nail-plate located on a recovering patient. Furthermore, the corrosion experiments shown that the joints are very stable when tested in vitro in a simulated physiological media.

The friction and wear behavior of advanced alumina ceramics for joint prostheses, centrifugally compacted (CC) alumina and hot isostatic pressing (HIP) alumina, were evaluated in uni-directional sliding test by using a pin-on-disk test apparatus. In the centrifugal compaction process, small alumina powder was compacted under a high centrifugal force and sintered under relatively low temperature condition. Thus, the average grain size could be substantially restricted to a sub-micron size. HIP was also used to modify the microstructure and mechanical properties. Three kinds of conventional alumina ceramics for joint prostheses and for industrial use were also examined, and their friction and wear behaviors were compared. Distilled water and diluted bovine serum were used as lubricants in the wear tests. After the test, the morphological nature of the worn surface of the alumina specimen was examined by SEM to consider the wear mechanism.

As a result, wear rates of CC alumina and HIP alumina were much smaller than those of conventional alumina ceramics. The improved microstructures, such as a small grain size and less flaws, and mechanical properties of advanced alumina ceramics would be responsible for such a good tribological behavior.

Biocompatibility of polarized strontium hydroxyapatite (SrHAp: Sr₁₀(PO₄)₆(OH)₂) ceramics was studied in terms of the bone-like crystal growth as well as the cell reaction. The ceramics of SrHAp were prepared from SrHAp powders were synthesized by a wet-method. The polarized ceramics were immersed for 12h, 1, 3, and 5 days in three types of media such as simulated body fluid, α-minimum essential medium (α -MEM),and α -MEM with included 10% fetal bovine serum.

The soaked ceramics were analyzed by X-ray diffraction, and grown crystals on ceramics surface were observed by scanning electron microscope. Crystals on negatively charged surface (N-surface) were well grown in every medium than those on the positively charged surface (P-surface). Cell cultivation revealed that osteoblast like cells (MC3T3-E1) grew on the surface of non-polarized and polarized ceramics for 1,3,and 4days. The MC3T3-E1 cells were more strongly adhered to N-surface than to P-surface.

A Na₂O-SiO₂ glass forms a bonelike apatite layer on its surface in a simulated body fluid (SBF). It has been assumed that a silica hydrogel abundant in Si-OH groups on its surface provides sites favorable for the apatite nucleation. In the present study, the mechanism of apatite formation on a 20Na₂O·80SiO₂ (mol%) glass in SBF was studied by X-ray photoelectron spectroscopy, etc. It was found that most of the sodium in the glass surface releases into the fluid within 12 h to form a silica hydrogel rich in Si-OH groups by the ion exchange with the H₃O⁺ ion. The Si-OH groups combine with calcium ions to form a calcium silicate within 12 h. The calcium ions combined with Si-OH groups combines with phosphate ions to form an amorphous calcium phosphate within 10 d. The amorphous calcium phosphate crystallizes into an apatite within 17 d. This indicates that the Si-OH groups do not directly induce the apatite nucleation, but through formation of a calcium silicate and an amorphous calcium phosphate.

As a candidate for highly loaded bone substitute, tantalum metal has attractive features such as biocompatibility, high malleability and ductility. The present authors previously showed that NaOH and heat treatments make tantalum metal to form a bonelike apatite layer on its surface in a short period, although even the untreated tantalum metal forms the apatite in a long period. In the present study, bonding strength of the apatite layer, which was formed on the NaOH- and heat-treated tantalum metal, to the substrate was measured under tensile stress and compared with that of the apatite formed on the untreated substrate. The former showed much higher bonding strength than the latter. The higher bonding strength of the former was attributed to a graded structure at the apatite-substrate interface where the apatite gradually changes into the interior metal substrate.

A macroporous titanium surface layer formed on titanium substrate was subjected to 5.0M-NaOH treatment at 60°C for 24 h and heat treatment at 600°C for 1 h. The NaOH and heat treatments produced an amorphous sodium titanate layer uniformly on the surface of the porous titanium. The sodium titanate induced a bonelike apatite formation in a simulated body fluid. Apatite layer could be thus formed uniformly along the surface morphology of the porous titanium. It is expected that the porous titanium layer subjected to the NaOH and heat treatments will not only enhance bone ingrowth into the porous structure, but also provide a biological integration with bone via apatite formation on its surface in the body.

Commercially pure titanium was treated with an H₂O₂/TaC1₅ solution. Thus formed titania gel layer remained amorphous when heated below 200°C and transformed to anatase after heated between 300-600°C. The anatase layers were substantially bioactive to deposit carbonate ion-incorporated apatite after soaked for 1 d in a simulated body fluid (Kokubo’s recipe), while the amorphous layers did not deposit up to 7 d. The apatite particles were preferably nucleated inside the cracks which prevailed in the titania gel layers. After soaking only for 2 d, the specimens were almost completely covered by the apatite. The H₂O₂-treated Ti specimens deposited apatite on both the contact and open surfaces, whereas the NaOH treated Ti specimens only deposited on the contact surfaces. The elimination of peroxide radicals out of titania gel and formation of anatase during heating are considered to be responsible for the improvement of apatite deposition ability.

Hydroxylapatite (HA) coatings on titanium alloy (Ti6A14V) implants are widely used in orthopaedics because the high strength of metals is combined with the osteoconductive properties of calcium phosphate (Ca-P). HA coatings are commonly applied on metal prostheses by plasma spraying. However, this technique presents important drawbacks: inability to cover porous implants and to incorporate biologically active agents, delamination and particles release. Recently, a biomimetic approach has been developed for coating metal implants. This method which mimics biomineralization allows the deposition of a bone-like apatite layer on metal prosthesis. In this study, cleaned and etched Ti6A14V samples were firstly immersed into a Simulated Body Fluid (SBF) solution at 37°C and secondly into SBF solution containing less inhibitors of crystal growth (e.g. Mg²⁺, HCO₃^-). A bone-like apatite layer of ≈15μm precipitated on the titanium alloy surface. Scratch testing showed that Biomimetic Apatite Coating (BAC) is more elastic than the brittle HA-PSC. Furthermore the dissolution rate of BAC is in the same range as HA-PSC. The biomimetic method can produce a stable and well adhered apatite coating on complex shapes at physiological conditions.

A calcium phosphate coating over porous chitosan sponges was produced by a process based on phosphorylation, Ca(OH)₂ treatment and SBF immersion. Porous chitosan sponges were prepared first by dissolving chitosan powder in acetic acid, and then freeze-drying. The obtained porous sponges were washed with ethanol containing sodium hydroxide. Sponges not subjected to the sodium hydroxide treatment were easy to dissolve in water. Sponges were phosphorylated by using urea and phosphoric acid in DMF solution. Phosphorylated chitosan sponges was soaked in saturated Ca(OH)₂ solution at ambient temperature, which lead to the rapid formation of calcium phosphate coatings and were found to stimulate the growth of a calcium phosphate coating on their surfaces after soaking in SBF solution. The mechanism of formation of the calcium phosphate coatings on the chitosan sponges must involve a diffusion of the phosphorus ion from the interior of the sponges, so creating a sufficiently high local concentration of ions at the surface to facilitate precipitation of calcium phosphate from the soaking medium.

Recently, we developed a novel alternate soaking process for apatite formation on/in organic 3-D matrix. This process is based on the widely-known wet process for hydroxyapatite preparation in which it is done by alternately soaking in CaCl₂/Tris-HC1 and Na₂HPO₄ aqueous solutions. In the present study, we report apatite coating on poly (acrylic acid) grafted poly(ethylene) films (PAAc-g-PE) with various PAAc densities. The amount of apatite formed on PAAc-g-PE films increased with an increase in the grafting density of PAAc when the grafting densities of PAAc were up to 30 μg/cm². Interestingly, the amount of apatite coated on PAAc-g-PE decreased when the grafting densities of PAAc were more than 30 μg/cm². From SEM observation, porous apatite crystals were observed on PAAc-g-PE of 30 μg/cm². On the other hand, plate-like apatite layer was found on PAAc-g-PE of more than 30 μg/cm². These results suggest that an alternate soaking process can be applied on polymer substrates for apatite coating, and that apatite crystal growth can be controlled by changing the grafting densities of PAAc. We think that these results also indicate new considerations of biomineralization.

Organic monolayer films with carboxyl groups were prepared by a Langmuir-Blodgett (LB) method. When the LB monolayers were soaked in a simulated body fluid (SBF), the nucleation of hydroxyapatite (HAp) took place on them. From infrared spectra analyses, it was found that an interfacial interaction between carboxyl groups and calcium ions was essential for the HAp nucleation. By transmisson electron microscopy, the HAp crystals were found to form plate-like single crystals whose (100) surfaces were wide, parallel to the inorganic/organic interface.

Hydroxyapatite films were formed on various substrates such as 12 mol% ceria-doped tetragonal zirconia (12Ce-TZP), 3 mol% yttria-doped tetragonal zirconia (3Y-TZP), alumina, monetite coated titanium (Ti/CaHPO₄) and calcium titanate coated titanium (Ti/CaTiO₃) via hydrothermal reactions of Ca(edta)^2- and 0.05 M NaH₂PO₄ at initial pH 6 and 160 - 200°C for 0.5- 6 h. Morphology of the film changed depending on the substrate, i.e. hydroxyapatite entirely coated the surfaces of l2Ce-TZP, Ti/CaHPO₄ and Ti/CaTiO₃ plates, but sparsely deposited on 3Y-TZP and Al₂O₃ plates. Film thickness increased with time (ca. 41 and 90μm on 12Ce-TZP for 2 and 6 h, respectively, at pH 6 and 200 °C). Adhesive strength of the film changed depending on the substrate as 12Ce-TZP(28 MPa) > CaTiO₃ coated Ti (22 MPa) > Ti/CaHPO₄ (9 MPa).

CaSiO₃ ceramics were prepared from coprecipitated powders using NaOH as precipitant with different washing treatments. The as-prepared ceramics differed in their Na content and Si/Ca ratio, which was reflected in their different microtextures. The grain size of the CaSiO₃ and the thickness of glassy phase at the grain boundaries increased with increasing Na content. These CaSiO₃ ceramics were soaked in a simulated body fluid (SBF) at 36.5°C for various periods of time. Precipitation of hydroxyapatite was observed as ball-like particles on surfaces of all the ceramics, but with different formation rates. The ceramics with smaller grain size showed a faster hydroxyapatite precipitation because the smaller CaSiO₃ grains easily dissolve, allowing the Ca²⁺ ion concentration and pH of the SBF to rapidly approach the suitable condition for precipitation of hydroxyapatite.

It was already revealed that a sol-gel-derived titania forms an apatite on its surface in a simulated body fluid (SBF). It is, however, not clear what structure of titania gel is effective for inducing apatite nucleation on its surface. In the present study, apatite-forming ability of titania gels with different structures, which were formed in different media and heat-treated at different temperatures, were investigated in SBF. The titania gels heat-treated at 300°C took amorphous phases and did not form the apatite on their surfaces even after 14 days irrespective of the media. The titania gels, which were prepared in media containing no additive or acetylacetone and heat-treated at 500 to 800°C to precipitate anatase, formed the apatite on their surfaces within 7 days in SBF. The titania gels, which were prepared in a medium containing diethanolamine and heat-treated at 700 to 800°C to precipitate rutile, formed the apatite within 14 days in SBF. This indicates that a specific structure of titania such as anatase structure is effective for inducing apatite nucleation.

Growth mechanism of hydroxyapatite (0001) face was revealed using hydroxyapatite single crystals as seeds. Hydroxyapatite was grown in a pseudophysiological solution and detailed surface morphology of (0001) face was observed by an atomic force microscope (AFM), indicating that the growth proceeded with a multiple two-dimensional nucleation mode. Growth rates of (0001) face in the pseudophysiological solution were measured by Moire shift interferometry. The growth rates were time-dependent. The growth rates gradually decreased with time and the growth finally stopped. The growth rates at an initial growth stage were about 8 × 10⁻² nm/s. It was also found that volume diffusion controlled the growth process during the initial 2 hours.

Calcium phosphate clusters approximately 0.8 nm in diameter were detected in a solution containing only CaC1₂, H₃PO₄ and KCl at 25.0°C using an intensity-enhanced dynamic light scattering (DLS) technique. This suggests that tris(hydroxymethyl)aminomethane used as a buffer had no contribution to the formation of the clusters. The clusters were also detected in a simulated body fluid (SBF) with ion concentrations nearly equal to those of human blood plasma and in a solution (1.5SBF) with ion concentrations 1.5 times the SBF at 36.5°C.

The measurement for bonelike apatite crystal growth rate on biomaterials in a simulated body fluid is very important. The crystal growth has been measured with scanning electron microscopic (SEM) observation. It is difficult to measure a dynamic behavior of crystal growth by using ex-situ measurement, such as a SEM observation. On the other hand, a quartz crystal microbalance (QCM) method is an in-situ measurement, which is suitable for the precise measurement of the crystal growth. A resonant frequency of quartz crystal is measured in the QCM method. This resonant frequency change corresponds to a mass change of a substance accumulated on the quart crystal. An amorphous calcium phosphate was deposited on the quartz crystal covered with gold using rf-magnetron sputtering. Then the calcium phosphate was annealed under water vapor pressure in an autoclave at 200°C for 24 h, in order to obtain a high crystalline HAp. The crystal growth on this substrate in a SBF was measured with QCM method. From this measurement, the mass change on the substrate was obtained. The deposited compounds was assigned to bonelike apatite from x-ray diffraction method and Fourier transform infrared spectroscopy. Using this substrate, the mass change directly corresponding to the crystal growth on HAp was precisely measured.

A layer of Ca/P was produced on a porous cellulose sponge by making use of a biomimetic method. The first step, the exposure of cellulose to the bioactive glass (BAG) S53P4, was made at 37 °C for 24 h with the substrate not in contact with the BAG. In the conventional method the substrate is contact with the BAG. Apatite growth was allowed to take place at the same temperature for varying periods of time up to 81 days. After 81 days treatment the apatite-layer covered most of the fibres of the organic matrix as indicated by modified von Kossa staining and by scanning electron microscopy (SEM), which revealed a homogenous but rough and hillocky layer of crystalline hydroxyapatite. The coating was further characterized by X-ray diffraction (XRD) and infrared spectroscopy (FTIR). XRD analysis indicated that formed Ca/P layer was amorphous and after 7 days crystallinity of the apatite-like layer was increased. FTIR showed that formed layer was carbonated hydroxyapatite.

The surface morphology and surface potential of the hydroxyapatite (HAp) ceramics with and without electrically poling were first investigated by tapping mode atomic force microscopy (TMAFM) combined with surface potential microscopy (SPoM). The HAp ceramic specimens were prepared by sintering the compact bodies of wet-chemically synthesized powders at 1250°C for 2 h under H₂O flow. The specimen was partially polarized in a do field of 1000 V cm⁻¹ for 1 h in air at 300°C. The surface potential distribution on the HAp specimen were significantly different between unpolarized surface and polarized one; the surface potential of polarized HAp region was higher than that of unpolarized one. The acceleration and deceleration of in vitro bonelike crystal growth on HAp ceramics soaking in a simulated body fluid solution could be related to the surface potential change caused by the electrically poling.

The development of high surface area and adequate porosity have been claimed as responsible for the high bioactivity exhibited by sol-gel glasses when immersed in a Simulated Body Fluid (SBF). However, the fast growth of a phosphate-rich layer on the surface of bioactive materials when exposed to physiological conditions, confers this layer the key role in determining the nature of the biomaterial/bone interface. The objective of this study has been to evaluate the surface properties of the phosphate layer developed on the surface of a SiO₂-CaO (CaO = 20 mol%) bioactive gel-glass by immersion into SBF. The growing process of the calcium phosphate layer has been monitored by SEM/EDS, TEM/ED and XPS. A calcium phosphate layer started to form very rapidly, covering most of the glass surface at only 3 h. Silicon is detected by XPS in the sample fully covered by calcium phosphate, which suggest that it is present during the whole crystallisation process at the phosphate/solution interface.

The bioactivity of electrolytically coated hydroxyapatite (HA) on titanium substrates was investigated and compared with titanium sheets with three different surface treatments: machined, blasted with Al₂O₃ and plasma-sprayed with titanium. This paper reports the results of an in vitro study using simulated body fluid (SBF). The specimens were examined by scanning electron microscopy (SEM), and X-rays diffraction spectroscopy (XRD). The SBF solutions of each specimen were analysed by ICPMS. SEM analysis after 7 days of incubation showed hydroxyapatite precipitation in the HA coated specimens, and this was confirmed by the XRD and ICPMS analysis. The SEM and XRD analysis indicated the absence of HA precipitation in the non-coated specimens, even after 35 days.

Niobium can replace vanadium in Ti-Al-V alloys in order to avoid the slow accumulation of potentially harmful vanadium ions. Niobium is known to be a biocompatible material; however the role of its addition on bone-implant adhesion is not well known. In order to investigate this problem, a detailed thermodynamic analysis concerning the nucleation of a calcium phosphate coating on the niobium surface immersed in a body fluid solution (SBF) was carried out. With this purpose, Eh-pH and pi-pH diagrams of the Na-Nb-H₂O and Ca-Nb-H₂O systems were constructed. It was verified that a sodium niobate layer will form during chemical pre-treatment of the alloy in NaOH solution. This layer is replaced by calcium niobate during the subsequent exposure of the alloy to the SBF solution. From the pCa-pH diagram of the Nb-Ca-P-H₂O system, the thermodynamic stability of the niobate-apatite, Ca₁₀(PO₄)₆(NbO₃)₂, over a wide range of pH values was characterised. This is a good indication that niobium do not alter the mechanism of hydroxyapatite precipitation, guaranteeing in this way the strong chemical adhesion provided by the biomimetic process.

Biological behaviors, characterization and crystal growths on the electrically poled hydroxyapatite (HAp) ceramics were investigated. The specimens were electrically poled in a do field. Bone-like crystal growths were studied in a simulated body fluid (SBF) with pH 7.25 at 36.5°C, and in an alpha minimum essential medium. Grown crystal layers were observed by scanning electron microscopy, and were analyzed by X-ray diffraction and Infrared spectroscopy. As a result, the bone-like HAp crystals grew rapidly on the negatively poled surface (N-surface), while the growth was restricted on the positively poled surface (P-surface) in SBF. It was considered that the aligned dipoles of substrate accelerated the crystal growth on the N-surface, and decelerated on the P-surface. Biological behavior was estimated by the cultivation of osteoblastic and fibroblastic cells on the surface of poled HAp. Cultured cells were found on the grown bone-like crystal layers for the N-surface, while the cells were directly on the specimens for the P-surface. On the poled HAp ceramics, N-surface had more adhered cultured cells than the P-surface.

The effect of low levels of silicon-substitution on the biocompatability, bioactivity and the surface apatite layer forming ability of hydroxyapatite was demonstrated by studying three different compositions: stoichiometric HA and 0.8 and 1.6wt% silicon substituted hydroxyapatite (Si-HA). The apatite-forming ability of the three compositions was determined by immersing the samples in Simulated Body Fluid (SBF K-9). Thin Film X-ray Diffraction (TF-XRD) and Scanning Electron Microscopy (SEM) showed that the time required to form a surface apatite layer (SAL) decreased with increasing silicon substitution. A human osteosarcoma (HOS TE 85) cell line was used to evaluate the effect of incorporating silicon into the lattice of HA on its in vitro biocompatability. A MTT assay indicated that all samples were non-cytotoxic and the mitochondrial activity of the cells cultured in eluates obtained from the 0.8wt% Si-HA showed a statistically significant increase compared to the negative control (Thermanox^TM) and stoichiometric HA. From the results of the alamarBlue^TM assay, the metabolic activity of HOS cells on 0.8 and 1.6wt% Si-HA compositions was increased for all time points, compared to stoichiometric hydroxyapatite. This study has shown that silicon-substituted hydroxyapatite bioceramics enhance the formation of a surface apatite layer in an artificial physiological solution and stimulate osteoblast-like cell activity in vitro, compared to stoichiometric HA.

Four batches of carbonate-substituted hydroxyapatite discs, designated CA1, CA2, CA3 and CA4, were prepared with carbonate contents of 5.4, 6.1, 8.2 and 11.3 wt%, respectively. The biological response to these materials was compared with the response to stoichiometric hydroxyapatite (HA) by biochemical evaluation of human osteoblast-like cells (HOBs) incubated both in direct contact with the discs and in culture medium containing solutes from the five substrates. Assessment of the cellular response to solutes from the five substrates demonstrated enhanced activity in those cells exposed to CA3 discs. Biochemical and morphological assessment of HOBS in direct contact with the disc surfaces supported this finding with enhanced proliferation being achieved in cells incubated on CA3 discs as compared to HA. However, while the response to CA4 was found to be comparable to the HA, proliferation was suppressed in cells incubated on CAl and CA2 discs, as confirmed by the poor morphological appearance of cells on these discs, apparently due to increased ceramic solubility leading to a degradation in the cell/substrate interface. This indicates that HOB cell metabolism is highly sensitive to the precise level of carbonate ion substitution, which in low carbonate HA reflects the solubility of the material. Moreover, the optimum level of carbonate substitution has been identified as similar to that found in bone mineral.

Four different assays, monitoring different aspects of cellular activity were used to assess the in vitro biocompatibility of three experimental zirconias (ZrO₂-A, ZrO₂-B and ZrO₂-C) with minor chemical modifications. The assays used were Neutral red uptake, MTT, alamarBlue and a live/dead cell stain. No cytotoxic effect was detected in the extracts from the three test zirconia samples using Neutral red uptake and MTT assays. However, a variation in response was observed in cells cultured directly on the surface of three test zirconias using the alamarBlue assay. The three test zirconia substrates showed no toxic effect after 1 and 2 days in culture. After 5 days in direct contact with the experimental zirconias, a significant decrease in cell activity was observed on sample ZrO₂-B, which was confirmed by fluorescence microscopy, showing a layer of dead cells (stained by thidium homodimer-1) on the sample surface. The findings from this study indicated that great care is required when selecting assays to assess the biocompatibility of modified materials with regard to the type and sensitivity of the assay and culture conditions.

The object of the present study was to supplement Electron Microscopy itemized account and a review of biological aspects of the recently reported upgraded phosphate powder and ceramic (HA-SAL2)¹. The biological tests include : (1)Growth in vitro, on ceramic cells, of cells relevant to osteogenesis. These cells attached and spread well, forming healthy and organized layers in shorter times than on commercial ceramics. (2) Cytokine release determined by incubating in vitro HA-SAL2 powder with human monocytes from healthy donors indicated induction of IL-1β IL-6 release within normal levels. (3) Soft tissue reactions in vivo: powder samples were implanted subcutaneously in rats. Histology of the tissues did not show inflammation or adverse cytotoxicity. (4) mineralization of rat tibial defects implanted with HA-SAL2. The mineral content of the defects, followed by a novel noninvasive DEXA technique showed faster healing than with a commercial implant product.

We prepared zinc-containing TCP/HAp ceramics (Zn-TCP/HAp) in the shape of disk, and examined the effect of zinc on the osteogenic differentiation of cultured marrow cells on the surface of Zn TCP/HAp. Fresh marrow cells were obtained from the femora of Fischer rats and cultured in a medium containing 15% fetal bovine serum to reach confluent. After trypsinization, the cells were seeded at 20×10³ cells/16 mm ϕ on Falcon tissue wells with the ceramic disk for subculture. Just before the cell seeding, three different disks (TCP/HAp containing 0, 0.126, or 0.316 wt% Zn) were placed in the wells. After 2 weeks of subculture in the presence of β-glycerophosphate, vitamin C phosphate, and dexamethasone, the cells were stained for alkaline phosphatase (ALP). The ALP positive area on the Zn-TCP/HAp disk was expanded with an increase in Zn content, as covering almost the entire surface of the Zn-TCP/HAp disk of 0.316 Zn wt%. The results indicate that the Zn doped TCP/HAp ceramics stimulate osteoblastic differentiation in cultured marrow stromal cells.

B cells differentiate in bone marrow from hematopoietic stem cells to immature B cells under the influence of bone marrow microenvironment. In in-vitro culture of B lineage cells, the stromal cell line can substitute for bone marrow microenvironment, supporting preB cells in the presence of interleukin 7 (IL-7). Because we consider that stromal cell culture on the flat plate is not enough to modify the bone structure, porous hydroxyapatite ceramics (HA) on that osteogenic differentiation occurred by bone marrow stromal cells were utilized for mimicking bone marrow microenvironment. Bone marrow cells and spleen cells were cultured on porous HA coated with a stromal cell line in the presence of IL-7. After 7 days culture, new population of preB cells were appeared, which are characteristic for next 3 items. 1). B220 low, BP1⁺ and CD43⁺ preB cells. 2) The surrogate light chain (VpreB and Lambda 5) positive preB cells were present. 3). PreB cells from spleen cells of a 7 weeks old adult mouse were populated. It is extremely interesting to note that this is the first demonstration of the presence of preB cells derived from adult spleen. All established preB cells can differentiate into IgM⁺ immature B cells. We speculate that porous HA coated with stromal cells can stabilize fragile cells specifically responding IL-7, demonstrating that porous HA provides different circumstances compared with flat plates.

Synthesis and applicability of silicate apatite containing rare earth elements as biomaterial were studied for biomedical use. Barium lanthanum oxide silicates (Ba_2+xLa_8−x(SiO₄)₆O_2−x/2) were synthesized by solid state reaction using BaCO₃, SiO₂, La₂O₃ at 1400°C in air for 2h. The powder (Ba₂La₈ (SiO₄)₆O₂) thus obtained was identified single phase of barium lanthanum oxide silicate (apatite type) by XRD. There were oxyapatite, as was confirmed by IR revealing hydroxyl by IR. Compositions of the apatite were analyzed by ESCA, EDX. Ba₄La₆ (SiO₄)₆O was sintered. The relative density of 96% was obtained under condition at 1400°C in air for 2h. Barium rare earth oxide silicates (Ba_2+xLn_8-x(SiO₄)₆O_2−x/2 Ln= Pr, Nd, Sm, Eu, Gd) were synthesized by the same condition as that of barium lanthanum oxide silicate. The samples were formed to pellets for the biocompatible experiments with osteoblast-like cell (MC3T3-El) and fibroblast cell (L929). Cell behaviors on barium lanthanum oxide silicates were observed by SEM. The number of cells which adhered on the samples surface were observed. These results comfirmed biocompatibility of barium rare earth oxide silicates.

Effects of porous hydroxyapatite granules (HAGs) on osteogenesis were examined in vitro using cells from adult rabbit femurs. Cultures in the space of 30-600 μm between glass plates with two-dimensionally arranged HAGs on the horizontal bottom glass surface induced thin insular tissue formation within 2 weeks. It was induced earlier and more than that without HAGs. Von Kossa staining-positive tissues were found at 1-2 weeks after their formation, suggesting their mineralization. No cells or several cells in monolayer were included within some of them. Several grew quadrate tissues. Similar thin tissues were formed in inclined and rotated glass tubes with three-dimensionally arranged HAGs. They were almost irregular in shape. By contrast, little extracellular matrix deposition and no mineralization were seen in the spaces over 600 μm and under 30 μm between the glasses with HAGs. These results suggest that osteoblastic cells from adult femurs form mineralized quadrate tissues with or without embedded cells on the horizontal glass in the space of 30-600 μm, while mechanical loading without system induces irregular-shaped tissue formation. Porous HAGs in the space seem to accelerate extracellular matrix accumulation and its mineralization.

Cbfal is a transcription factor, which belongs to the runt-domain gene family. Cbfal is expressed in osteoblasts and chondrocytes, and its expression is increased according to their maturation. Cbfal has two isotypes with different N-terminal domains, and the two isotypes show different activities in the regulation of their target genes. Cbfal-deficient mice showed a complete lack of bone formation in the absence of mature osteoblasts, and forced expression of Cbfal in mesenchymal cells induced osteoblastic markers, indicating that Cbfal is an essential factor for osteoblast differentiation. Chondrocyte maturation and osteoclast differentiation was also blocked in mutant mice. RANKL was barely detectable in Cbfal-deficient mice, suggesting that Cbfal induces osteoclast differentiation by the regulation of RANKL in osteoblastic cells. These data demonstrate that Cbfal plays an essential role in bone formation.

Jaw bone, such as alveolar bone for tooth socket, has many characteristics and remodeling mechanisms dissimilar to the other bony tissues. This study aimed to clarify the healing mechanism and process of jaw bone formation in the case of mandible bone defect in dog using porous hydroxyapatite-BMP composite. 70% porosity and 100-200 micron meter pore sized HAP and BMP composite was implanted into artificially scooped out mandible bones of dog. After one week, the HAP-BMP composite accelerated osteoblast differentiation and osteoid formation in contrast to the BMP implant experiments that showed no bone formation. Around HAP-BMP composite, immature bone formed after one week and definite fibrous bone formation was observed after three weeks. It was observed that after one week fibrous tissue surrounded the HAP-BMP composite and there was little or no direct evidence of osteoconduction from the surrounding bone. After five weeks, newly formed bone was substituted by mature bone with remodeling similar to healing process. After remodeling process started osteoconduction was clearly observed. The results suggested that in dog jaw bones HAP-BMP composite introduced mesenchymal cells differentiation at the early stage and influenced to activate these cells and bone formation.

Concave defects in bone after tooth extraction often cause various difficulties in prosthetic dentistry, which require an effective method of local bone recovery. We have devised porous particles of hydroxyapatite (PPHAP) for bone augmentation. Recombinant human BMP2 was combined with PPHAP and implanted into the sockets after extraction of premolars in rabbit mandibles. Control groups with PPHAP alone, and without any implant were designed. Quantitative histological analysis of bone formation was done in the divided areas within the socket, the orifice, middle, and, bottom areas in the apical direction, and also in the central and lateral wall areas in the horizontal direction. Four weeks after operation, in the non implant and the PPHAP-alone groups, active bone formation was limited to the bottom and lateral wall areas. Little bone formation was observed in the central and orifice areas. On the other hand, in the BMP2/PPHAP group new bone formation was seen as early as in 2 weeks in almost all areas of the socket. After 4 weeks, total amounts of new bone in the BMP2/PPHAP group were about two times higher than in the control. The bone formation was particularly rich in the orifice areas, resulting in the flat or convex-shaped recovery of alveolar bone after tooth extraction. This application of the rhBMP2/PPHAP composite material will provide a useful tool in clinical dentistry.

Hard cement cylinders (4 × 5 mm) made of a bioresorbable calcium phosphate cement (BCPC) were soaked with 6.28 and 1.26 μg of rhBMP-2. These cylinders with and without BMP were implanted subcutaneously into the back of SD rats. After 3 weeks, these cylinders with newly induced bone tissue were removed and reimplanted into the 5 mm segmental bone defect created in the femur. Three weeks after the reimplantation, osseous continuity of the 6.28 μg group was restored. The osseous replacement of the cement of the 6.28 μg group progressed and the cement cylinder was completely replaced into bone tissue at 9 weeks. Mechanical test showed that 70 % of the 6.28 μg group and 80 % of the autogeneous bone graft group united but that no case of other groups united. The tortional failure torque of both the 6.28 μg group and the autogeneous bone graft group was 62 % of that of the contralateral intact femur.

The results of this study support the potential application of the transplantation of the BCPC with subcutaneously induced bone as a bone-graft substitute.

A composite of marrow mesenchymal stem cells and porous hydroxyapatite (HA) has in vivo osteogenic potential. To investigate factors enhancing the osteogenic potential of marrow/HA composites, we used recombinant human bone morphogenetic protein-2 (rhBMP-2). Marrow/HA composites or composites containing marrow mesenchymal stem cells, rhBMP-2, and HA (marrow/BMP/HA composites) were implanted subcutaneously in 7-week-old male Fischer rats. BMP/HA composites and HA alone were also implanted. The implants were harvested after 2 and 4 weeks. Histologically, obvious de novo bone formation together with active osteoblasts was seen at both 2 and 4 weeks in many pores of the marrow/BMP/HA composites. The marrow/HA composites did not induce bone formation at 2 weeks, but showed moderate bone formation at 4 weeks. In contrast, neither the BMP/HA composites nor HA alone induced bone formation at any time after implantation. These results indicate that the combination of marrow mesenchymal stem cells, porous HA, and BMP synergistically enhances osteogenic potential and that the composites can be utilized effectively in osseous reconstructive surgery.

In this study the incorporation of resorbable, porous surface modified bioactive ceramics (pSMC) was investigated in a long bone defect. In order to promote osteogenic activity, two tissue engineered constructs were examined: 1) rat bone marrow stromal cells were seeded on pSMC two hours prior to implantation (primary) or 2) cells were expanded on pSMC for 2 weeks to synthesize bone prior to implantation (hybrid). A unicortical window defect was created bilaterally in the femoral diaphysis of 96 adult, male Fisher rats (350-400g). Defects were treated randomly with pSMC, primary, hybrid, or left untreated (sham) to compare healing rates at 2,4, and 12 weeks. Femora were tested in torsion and examined by histomorphometry.

At 2 weeks, long bones treated with the hybrid and primary constructs had 40% higher % bone in the defect than pSMC and the hybrid had the highest stiffness, which was comparable to intact bone. Primary and hybrid had comparable stiffness and strength to intact bone by 4 weeks. At 12 weeks, there was 40% bony ingrowth and 40% reduction in % scaffold for all treatment groups. PSMC achieved similar mechanical properties of intact bone by 12 weeks. Both tissue engineered constructs achieved early and similar rates of repair.

Bone-forming cells first fabricate a highly organized oollagen matrix, osteoid, which subsequently mineralizes. A variety of cell culture systems exist for osteogenic cells, yet none of these is optimal for the well-organized formation of a mineralized matrix. We have generated collagen substrates which have different degrees of fibrillar orientation, and have cultured osteogenic cells on these matrices. Osteoblast-rich cells isolated from 16 day chick embryos were cultured in micro-mass culture on the collagen sheets. Von Kossa-stained sections showed that highly oriented collagen matrix started to calcify in 6-7 days while a random fibrillar matrix did not mineralize even in 21 days. Mineral has been detected only within the collagen matrix with a narrow unmineralized region between the cells and the mineral like osteoid in vivo. The in vitro system described may serve as implantable materials facilitating in situ cell-mediated bone repair ultimately.

Trilateral research methods are developed by the author integrating morphology, molecular biology (physiology and biochemistry), and molecular genetics of remodeling by means of biomechanics. Through this research method the author develops artificial bone marrow chamber using bioceramics.

The author discovers through studies on evolution of hemopoiesis that the morphology of an organism can be changed by vicissitudes of inner or outer stimuli of biomechanics, i.e., environmental factors, which act to the organism, and if these vicissitudes of biomechanical stimuli are transmitted to the next generation morphological changes can be transmitted. Through this discovery the use and disuse theory of Lamarck can be explained biomechanically in molecular genetics.

Experimental evolutionary studies are carried out as follows: developing artificial bone marrow biochambers, the author has implanted them into archetype vertebrates as well as mammals, compared them each other, and analyzed them. Developments of hemopoiesis in bone marrow chambers in phylogeny are evident as the action of the gravity in terrestrialization, which is converted into heightening of blood pressure in chondrichthyes. As conclusion use and disuse theory is evidenced in second revolution of vertebrates for the gravity to trigger genetic expression in mesenchymal cells not only producing hemopoiesis conjugated with ossification of the cartilage but inducing major histocompatibility complex (MHC).

Bone formation was investigated by ectopic implantation of bioresorbable macroporous calcium phosphate (CMP) matrices combined with rat marrow cells of the athymic mouse. CMP matrices used were macroporous with about 200 μm pore size. CMP matrices were soaked in the subcultured rat marrow cell suspension adjusted to 5 × 10⁷ cells/ml for 30 minutes and then implanted into subcutaneous sites of an athymic mouse. The matrices recovered after 4 and 6 weeks and then uncalcified ground sections were prepared for histological examination. Osteogenesis could be observed in the pore regions at 4 weeks after implantation without fibrous encapsulation. This study thus suggested that the composite grafting of macroporous calcium metaphosphate matrices with marrow derived mesenchymal cells may be useful for repair massive bone defects.

We examined the long-term result of rhBMP-2(recombinant human bone morphogenetic protein-2), delivered in a IBM (insoluble bone matrix) particles implant, on heterotopic bone formation in rats in order to evaluate the IBM delivery system, and look forward to finding an effective carrier which can be applied clinically from this clue.

Chondroblast cells conforming to the shapes of lacunae with the basophilic matrix were merely observed at one and two weeks after implantation. The chondroid tissue was partially absorbed at two weeks after implantation. Bone formation and remodelling was noticed from two weeks. Both endochondral and intramembranous ossification were observed and the former was predominant at two weeks. Bone marrow-like structure was observed at three weeks and fatten marrow was found from four weeks. From seven weeks after implantation, new bone formation and absorption were not active. The IBM particles which covered by new bone were also in a stable state, and by the end of 9 weeks the mature bone tissue was still existent. Thus rhBMP-2 and IBM composites has high osteoinductive capability and the newly formed bone is relatively stable for a long time. This results indicate that IBM provides a excellent delivery system in early period of rhBMP-2 induced bone formation. After the remodeling of new bone, IBM seem to be turned into a part of bone matrix.

Osteopontin(OPN), one of the major non-collagenous bone proteins, has an important role in bone remodeling. OPN not only has a role in triggering the osteoblast early differentiation, but activates osteoclast resorption function. On this point of view, we proposed a model for bone remodeling via integrin-OPN binding, by which OPN could act as a signaling molecule between osteoblasts and osteoclasts in the remodeling procedure. Moreover, OPN proved to induce the in vivo osteogenic potential of bone marrow derived osteoblasts/hydroxyapatitc(HA) construct.

Microgravity in space has been reported to enhance bone resorption in vitro and in vivo, however, the gravity effect on bone remodeling is not well understood. In particular, there are only a few reports about gravity effect on osteoclasts. In the present study, we examined the hypergravity effect on mRNA expressions of osteoclast marker enzymes such as TRAP (tartrate-resistant acid phosphatase) and cathepsin K. Osteoclasts were exposed to 30 xg for 2 hr or 18 hr. Results suggested that hypergravity enhanced the mRNA expression of both enzymes with different manner; the expression of the TRAP showed a slight increase, that of the cathepsin K showed a non-monotonous time course with maximum hypergravity effect for short time (2 hr) incubation.

The mechanism of osteoclasts attachment to the bone surface has not been well understood. In particular sealing zone is a very specific structure of active osteoclast on bone. The molecular basis on its formation has recently attracted much attention in biologists. In this study, we have performed differential display (DD) PCR with the template RNAs extracted from osteoclasts cultured on ivory or collagen type I to identify genes specifically expressed in osteoclasts attached to ivory. Highly enriched osteoclasts were harvested from 10-day-old rabbit according to the method of Kakudo et al. and cultured on each surface. DDPCR was performed using their total RNAs, then PCR products were cloned into pCR-TRAP vector, followed by the DNA sequencing. 22 cDNA fragment clones were found in osteoclast attached to ivory. Among them, 11 clones which located at 3’terminal of related genes were sequenced. Two of them were found as known genes, i. e. PTX3 and DRAK 1. We selected 6 clones and examined tissue distribution by slot blot. The data showed that 6 clones expressed in various pattern. These result indicated that different pattern of gene expression was revealed when osteoclast attached to different matrix. It also suggested osteoclasts could form the effective sealing zone with the participation of multiple genes.

Hydroxyapatite (HA) has been used successfully for anchorage of endoprostheses. Data regarding the cellular resorption of HA coatings are varying. Until now it is not clear, why some HA materials were degraded by osteoclasts and others were not. In these cases foreign body giant cells (FBGC) were observed. In this study three different HA materials with different crystal sizes were tested. Only microcrystalline HA (crystal size in the range of human bone crystals) was resorbed actively by osteoclasts. Typical lacunae were observed in the surface of the material. If the crystal size of HA was higher (0.1-0.3 μm or 1-3 μm) lacunae were not observed any more. In such cases FBGC were detected on implant surfaces. In all three implant types tested bone bonding was observed in a similar amount. The data obtained are important with regard to the design of bioactive materials to special needs, e.g. coatings of endoprostheses.

Three kinds of bioactive particles of 45S5 Bioglass®, synthetic hidroxyapatite and A-W glass ceramic were implanted into 6 mm diameter holes made in the femoral condyles of mature rabbits. Bone-ingrowth rate was measured by means of an image processor for analytical pathology. 45S5 Bioglass® led to the most rapid bone proliferation, and at later periods found to be more resorption than A-W glass ceramic though synthetic hydroxyatatite was not resorbed.

If the calcium phosphate ceramics are the more common bone substitute used in human surgery, the process and kinetics of resorption and bone ingrowth at the expense of the material still not enough determined. The present study is a retrospective study of more than 300 implants of macroporous biphasic calcium phosphate used both in human and in some animal experiments. The bone ingrowth during the first year in both human and animal is limited to 2.5mm from the surface of the implants. The bone ingrowth over 2.5mm depends of the mechanical strain on the implantation site acting on the remodeling of the first bone ingrowth filling the macroporores. The image analysis revealed in cortical site after one year (both in human and animals) 50% of the ceramic was replaced by cortical lamellar bone. In cancellous bone, large differences appeared between animal species and in human, due to differences in cell recruitments.

Poling effects of hydroxyapatite (HAp) ceramics were studied on histological reaction. The sintered HAp ceramics were cut and sliced for rectangular plates (5 × 8 × 0.5mm). These specimens were electrically poled (surface charged) in a DC field of 1000 V/cm for 1 h. The poled HAp ceramics were implanted in bones of beagle dogs. The bones with the poled HAp samples were extracted after 3 and 7 days implantation. The histlogical reactions were estimated with the decalcified sections stained by hematoxylin eosin (H-E) and toluidine blue as well as the non decalcified sections by H-E, toluidine blue and Villanueva bone stain. New bone formations were observed on the negatively poled surface (N-surface). No contacted new bone formations but blood cell liners were observed on the positively poled surface (P-surface). Non poled HAp phases (0-surface) showed the intermediate reaction between the P- and N-faces. It was suggested that poled HAp vectored the cells and lured on the N-surface, whereas the P-surface had inhibitory effects on cell adhesion.

We recently showed that pure titanium metal chemically treated with hydrogen peroxide solution containing tantalum chloride has the ability to bond to bone directly. The purpose of this study is to examine effectiveness of the treatment on titanium alloy. The treatment was applied to a Ti-6A1-4V cylinder (4.0 mm in diameter, 20.0 mm in length). The specimen was implanted into a whole (4.0 mm in diameter) in a rabbit’s tibia. After implantation for predetermined periods up to 8 weeks, the specimens were extracted with bone tissue, and were examined by push-out test to evaluate the shearing force between the implant and bone tissue. The results were compared with those of non-treated titanium alloy as well as of pure titanium metal. Four weeks after surgery, the shearing force of the treated titanium implanted was higher than that of the non-treated titanium. Comparing titanium alloy with pure titanium, no significant difference was found at 4 and 8 weeks after surgery. Thus, it is confinned that the treatment with hydrogen peroxide solution containing tantalum chloride can provide Ti-6A1-4V alloy with bone-bonding ability, based on a similar mechanism on pure titanium metal.

This study was carried out to investigate the effects of alkali and heat treatments on the bone-bonding behavior of porous titanium implants. A porous titanium rod, 6 mm in diameter, was manufactured. This rod had 4.6 mm solid core and 0.7 mm-thick porous outer layer using pure titanium plasma-splay technique. This rod was cut transversely into pieces of 13 mm long. Three kinds of porous implants were prepared from these pieces: 1) control ; as manufactured (CL), 2) AW- glass ceramic bottom coated (AW), 3) Alkali- and heat-treated (AH) (5 mol/LNaOH 60°C for 24 h and 600°C 1 h). The implants were inserted into canine femora hemi-transcortically. At 4 and 12 weeks after implantation the bone-bonding shear strengths of the implants were analyzed with push out test and histological and histomorphometncal analysis were also performed At 4 weeks the AH implants showed significantly higher shear strength than the CL implants. At 12 weeks there was no significant difference among the bonding strengths of the three types of the porous implants. There was no difference in bone ingrowth into porous portion of the three types of the implants at both 4 and 12 weeks, while direct bone contact with implant surface was significantly higher in the AH implants than the CL and AW implants both at 4 and 12 weeks. In conclusion, alkali and heat treatments can provide the porous titanium implants with earlier stable fixation.

11 cavities were prepared in the upper lumbar vertebrae of 5 sheep. The cavities were 3 mm in diameter and were filled by percutaneous injection of nacre powder or PMMA. The lumbar vertebrae were removed after 3 months. Histological studies showed that there was still nacre powder in the cavities wich contains also a large active bone marrow cell population. The particles of nacre appeared to be in the process of dissolution. In contact with or adjacent to nacre there were layers of newly formed bone that was physiologically active.

We have developed a new artificial intervertebral disc prosthesis consisting of a triaxial three-dimensional fabric (3-DF) woven by an ultra-high molecular weight polyethylene fiber and spray-coated bioactive ceramics on the disc surface. The arrangement of weave properties led to the mechanical behavior of 3-DF disc similar to the natural intervertebral disc. Using a sheep model, total intervertebral replacement using 3-DF disc either coated by hydroxyapatite or apatite-wollastonite glass ceramics was conducted with or without initial fixation. Without the use of initial fixation, interface bony union was detected, however, the segmental motion decreased at six months postoperatively. The use of temporary fixation provided a nearly physiological mobility as well as the increased fusion rate at six months. A scanning electron microscopy showed that each fiber of 3-DF disc had a direct contact to trabecula. This study first highlighted the in vivo effectiveness of artificial intervertebral disc experimentally, and clarified further problems in clinical application.

The pulp was amputated at several levels in mandibular first molar canals of rats to determine whether a correlation exists between the amputation level and hard tissue formation. Tetracalcium phosphate containing cement (TeDC-Mc) was placed on a surface of amputated pulp and the chambers were sealed with a light curing resin. Histopathological procedures were performed after 1, 2, 3 and 4 weeks of pulp treatments.

Three weeks after the operation, hard tissue formed in 100% in the case placed TeDC-Mc at the root canal orifice, and formed in 85% of the case at the middle portion. In the case of pulp amputated at the apical foramen, addition of hard tissue was recognized in 15.8%. Radicular pulp exhibited necrosis and no addition of hard tissue was observed in the canals that had been amputated at the canal orifice with sealing of the chamber. In the periapical area instrumented beyond the apical foramen and placed TeDC-Mc, reconstruction of the alveolar bone was recognized at a later period in 95 %. The activity of undifferentiated mesenchymal cells and odontoblasts in dental pulp might contribute to hard tissue formation. Long periods are required for reconstruction of alveolar bone because of a lack of undifferentiated mesenchymal cells.

Biocompatible setting composed of octacalcium phosphate (OCP) in addition of α-tricalcium phosphate (α-TCP) was newly prepared. The OCP setting was formed by mixing monocalcium phosphate monohydrate and calcium carbonate with sodium hydrogen phosphate buffer (pH=7.4). Powder of αa-TCP was added to improve the mechanical properties of the OCP setting ranging from 0 to 100%. The setting with 69.0% α-TCP had a maximum compressive strength of 12.0±0.5MPa which was about 7 times as that of α-TCP free setting at 7 days suspension after preparation. Scanning electron microscopy (SEM) indicated the significant improvement was attributed to both the decreasing of porosity and homogenization of microstructure. The α-TCP/OCP setting transformed into brushite (DCPD) after immersion in Eagle’s minimum essential medium supplemented with 10% fetal bovine serum at 37°C for 24h, and changed to OCP and hydroxyapatite (HAp) phases after the 7 days’ immersion. The tissue reactions of the α-TCP/OCP setting with 69.0% α-TCP during setting in vivo were examined by subcutaneous tests using Wister rats. The histological observations after 6-week-implantation showed good biocompatibility with fibrous encapsulation of the settings. In vivo, the starting material transformed into HAp directly after 6-week-implantation without an intermediate product of DCPD in the setting reaction. It was assumed that pH was biologically maintained in vital environments.

High-strength hydroxyapatite (HA)/poly (L-lactide) (PLLA) composites for use as biodegradable fracture-fixation devices have been produced using a new compression molding method. The purpose of this study was to investigate the bone-bonding ability of these HA/PLLA composites. The composites contained 30% by weight of HA particles with a mean diameter of 3 μm. The initial bending strength and flexural elastic modulus of this composite were 280 MP a and 7.8 GP a, respectively. Rectangular plates made of this composite and of unfilled PLLA were implanted into the proximal tibiae of mature rabbits. Detaching tests and histological examinations were performed at 8 and 25 weeks after implantation. The tensile failure loads of the composite and unfilled PLLA were 1.39 kgf and 0.05 kgf at 8 weeks, and 2.60 kgf and 0.25 kgf at 25 weeks, respectively. There were significant differences between the composite and unfilled PLLA during the experiment (p< 0.05 at each point: two-way ANOVA). Histological examination showed that HA/PLLA bonded directly to bone throughout the experimental period, while unfilled PLLA exhibited intervening fibrous tissue between bone and plate. No inflammatory cells were found in the vicinity of either composite or unfilled PLLA plates, even at 25 weeks. These results indicate that the bone-bonding ability of the HA/PLLA composite could enhance fixation stability in the treatment of fractured bones.

The bone ingrowth in hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP) was not clearly explained in the past investigation. We understand this confusion was due to the difference of the porosity and pore size of the implant materials, and impurities and the heterogeneous chemical composition of the materials. In this study, pure HA and pure β-TCP with the same structure were implanted in the distal femurs of 24 mature male rabbits. The amount of ceramics and of regenerated bone were measured after 4, 12 and 24 weeks, respectively. There was a large amount of bone in β-TCP at 4 weeks, but they decreased at 24 weeks. Meanwhile there was the smaller amount of regenerated bone in HA at 4 weeks, but increased at 12 and 24 weeks, and then decreased after 24 weeks. The peak value of the amount of regenerated bone in HA and β-TCP was almost the same.

A porous-surfaced AWGC has been developed to offer a superior bioactivity and the initial strength with the high surface friction. Using seven male sheep, spinal defects created at L2/3 and L4/5 were reconstructed anteriorly with two types of AWGC and Kaneda SR. The animals were euthanized at six months after operation and spinal column was obtained. The interface between the AWGC and vertebral body was examined radiologically and histologically. In all cases of porous-surfaced AWGC, the bony union was observed radiologically between the porous surface of AWGC and vertebral body. Five of seven dense AWGC showed a complete displacement of prosthesis despite the rigid fixation. In only one case in which some displacement had occurred, the bone bonding was observed radiologically and histologically. Consequently, the porous-surfaced AWGC showed higher fusion rate compared with the dense AWGC. The high rate of dense AWGC dislodgment substantiates the mechanical superiority of high friction in poroussurfaced AWGC, increasing the initial interface stability.

This investigation shows that by a drastic increase in the pressure at hot pressing sintering there are possibilities to increase the fracture stress value and the mechanical strength of the carbonated apatite samples. It is also possible to obtain carbonate hydroxyapatite, containing the same carbonate content as from the start. However, the temperature should be kept below 1073 K. In this case, the final product will have a mechanical strength lower than that of bone. The carbonate hydroxyapatite is biocompatible.

CO₃apatite materials with a degradable outer layer and a relatively stable core were synthesized at 80±1°C and pH 7.4±0.2 by simultaneously feeding Solution I and Solution II into mechanically stirred 1.3 mol/L acetate buffer solution. Solution I consisted of 0.5 L of 100 mmol/L Ca(CH₃COO)₂; Solution II consisted of 0.5 L of 60 mmol/L NH₄H₂PO₄, into which 0.5 L of 60 mmol/L NH₄H₂PO₄ solution containing a constant concentration of 0, 48 and 95 mmol/L (NH₄)₂CO₃ was continuously supplied. X-ray diffraction (XRD) analysis showed a typically apatitic pattern and the (300) diffraction peak shift, indicating a CO₃-for-PO₄ substitution. SEM analysis showed changes in morphology: from needle-like to small aggregated crystals, confirming earlier reports on the effect of CO₃ on reducing apatite crystal size. Electron spectroscopic analyses of pelletized specimen showed a negative gradient of carbonate concentration with depth. The apparent solubility of the CO₃apatites in 0.5 mol/L acetate buffer solution (37°C, pH 4.0) increased with increasing CO₃ content. The CO₃apatites pellets were mixed with an atelocollagen whose antigenicity has been removed by enzymatic treatment and implanted into the periosteum cranii of rats. The composite showed good biocompatibility. In addition, the extent of biodegradation seemed to be related to the CO₃ content. These results suggest that CO₃apatite materials with controlled biodegradability can be useful biomaterials.

High Resolution Powder Neutron diffraction data were collected on samples of Ca₃ (PO₄)₂ (TCP) at temperatures ranging from ambient to 1525C. Data collected showed and almost linear expansion in unit cell dimensions for the β-TCP sample, followed by inversion to α-TCP at approximately 1300°C and finally inversion at 1500°C to super α-TCP. Data collected on the super α-TCP phase showed high tetragonal symmetry with a structure isomorphous with K2SO4. The structure of super -TCP waS refined using the Rietveld method in space group of P6₃/mmc with unit cell dimensions of a=5.3626Å and c=7.7017Å at 1525°C.

Monoclinic hydroxyapatite was prepared by a wet method and followed by heating in air at 1473 K for 1 h, and its phase transition was investigated by high temperature X-ray powder diffractometry and differential scanning calorimetry. The prepared hydroxyapatite is 98% monoclinic. The Rietveld refinement results revealed that the low temperature phase has monoclinic symmetry, space group P2₁/b and the high temperature phase has hexagonal symmetry, space group P6₃/m. In monoclinic hydroxyapatite, two different sizes of oxygen triangles exist. The rotation of phosphate tetrahedra at about 6° and the change of the hydroxyl order to disorder arrangement occurred due to the phase transition. The phase transition took place reversibly at 480.5(1) K in heating process and 477.5(1) K in cooling process with the enthalpy value of 130(1) Jmol^-1. Further, a sintered monoclinic hydroxyapatite was prepared. Discontinuity of dielectric curves was observed at 483 K The discontinuity of dielectric curves was concluded to the change of hydroxyl order to disorder arrangement.

In this investigation, three routes, namely, uniaxial pressing, slip casting and H₂O₂ foaming, were used to fabricate porous hydroxyapatite (HA). Processing parameters in each route were studied, pore characteristics in sintered bodies assessed, and mechanical properties of porous HA evaluated. Scanning electron microscopy, gas pycnometry and mercury intrusion porosimetry were used to assess pore characteristics in terms of porosity, pore size and pore shape. Mechanical properties of porous HA were evaluated using a biaxial testing fixture. The 2³ factorial design method was used to determine the influence of pore characteristics on mechanical properties. It was shown that pore characteristics were dependent on the manufacturing route, processing parameters, porosifier and the amount of porosifier. In the uniaxial pressing and slip casting routes, porosity, pore size and pore shape could be controlled using different porosifiers. Porosifiers were able to pass their geometrical characteristics to the pores they formed. Although H₂O₂ foaming was the simplest route and large pores could be formed through this route, pore characteristics were not easily controllable. It was found that porosity, pore size and pore shape all had effects on mechanical properties of sintered products. The interaction of pore size and pore shape affected mechanical properties in that it caused mechanical properties to vary differently according to pore shape (or pore size) when pore size (or pore shape) was at different levels.

The aim of the current work is to present a new route to synthesise carbonateapatite with low cristallinity and carbonate content in the range of biological apatites. Mechanical milling has been employed for this preparation and the influence of the different conditions on the final material characteristics has been studied. A higher time of grinding is required under a CO₂ atmosphere (210 hours) than under air (135 hours). However, in the sample obtained in air, some of the starting CaCO₃ still remains.

The dissolution/precipitation behaviors of hydroxyapatites (HA) derived from calcined cattle bone with and without chemical treatments (MP and TP respectively) were studied under human physiological condition. Both specimens were incubated in simulated body fluid (SBF) at 37°C with a sample surface area to solution volume ratio of 0.1 cm.^-1, 5%CO₂ was used to adjust pH of this solution to 7.40±0.05. The characteristics of MP and TP specimens were examined before and after incubation in SBF. The phase present and functional group of both specimens did not change after incubation for 90 days but the Ca:P ratio and bulk density decreased, hence the porosity increased. Furthermore, the newly formed precipitates appeared on the surface of both specimens after incubation for 30 days and covered all over the surface in 90 days. From the chemical analyses, it was found that this newly formed precipitates were calcium phosphate compound containing carbonate group in phosphate site structure, the phase of this compound was similar to natural cattle bone.

Adsorptive properties of hydroxyapatite (HAp) for proteins were studied by Quartz Crystal Microbalance (QCM) method. The time-series reactions of HAp thin films to acidic and basic proteins were analyzed in various pH buffers by the simultaneous resonant frequency and dissipation factor measurements. The amorphous calcium phosphate thin films deposited on the Au-electrode of quartz crystals by rf-magnetron sputtering were transformed into the polycrystalline HAp films by post-annealing treatment in hydrothermal atmosphere. Adsorbate solution was continuously injected by a tube pump at controlled flow rates into the QCM cell equipped with a PC added measurement system. The difference in adsorption for albumin and histone was detected from their resonant frequency shifts. It was suggested that the developed QCM system was effective for studies on protein adsorption behaviors onto HAp.

Hydroxyapatite (HAp) was synthesized in the presence of various types of amino acids; glycine (Gly), alanine (Ala), arginine (Arg), aspartic acid (Asp) and glutamic acid (Glu), as components of proteins, in order to investigate their effects on hydroxyapatite crystals. Glycine and alanine are neutral, arginine is a basic and aspartic acid and glutamic acid are acidic amino acids. Furthermore, we estimated the crystallinity and solubility of synthesized HAp. Analysis of X-ray diffraction demonstrated that all of the synthesized HAp had a typical X-ray diffraction patterns of HAp, whereas the crystallinity of HAp synthesized in the presence of either aspartic acid (HAp_Asp) and glutamic acid (HAp_Glu) decreased with the increase of the amounts of these acidic amino acids present. The solubility of HAp_Asp and HAP_Glu increased sigiificantly with the increase of the amounts of acidic amino acids present. The lower crystallinity of HAp_Asp and HAp_Glu observed in the current study was likely due to the adsorption of these amino acids on HAp. These results suggest that amino acids may play a major role in the regulation of crystallinity and solubility of HAp which is frequently used as a biomaterial for hard tissue diseases management.

Conventional precipitation routes for the production of hydroxyapatite require up to 3 days to progress from raw materials to powder product. One way of accelerating production is by microwave-assisted synthesis. To date, literature on the microwave-assisted synthesis of hydroxyapatite is scarce, and phase-purity of the sintered powders has not been addressed. This paper describes the microwave-hydrothermal synthesis of hydroxyapatite powder. The reactants used were AnalaR Grade Ca(OH)₂ in aqueous suspension and a solution of H₃PO₄. The microwave cavity used was a multimode domestic oven. By careful control of reactant calcium to phosphorus ratio and microwave operating conditions, phase-pure hydroxyapatite powder was produced (HA2). Second phases were not detected from XRD analysis of the as-precipitated powders On sintering the samples at 1200°C for 2 hours, only the sample HA2 was a single-phase hydroxyapatite. Reducing the reaction time gave rise to a secondary phase of TCP in the sintered product (HA1). Adding the H₃PO₄ in stages into the reacting mixture, gave rise to a secondary phase of CaO (HA3). The phase-pure hydroxyapatite powder (HA2) was found to have a median particle size of 51μm without processing.

Phosphate glasses are of a great interest for bone substitution materials, due to their chemistry close to that of the inorganic phase of bone and their unique property of being completely soluble. The aim of this study is to evaluate the kinetics of dissolution and the evolution of the mechanical properties of a phosphate glass in the system P₂O₅-CaO-Na₂O when kept in simulated body fluid (SBF). The results showed that the dissolution presented two different stages. In the first stage, the glass showed a mass loss varying at a rate proportional to t^0.55 and, after a certain time, the kinetics turn to linear dissolution. The mechanical properties during the dissolution of the glass showed values of E between 48 and 57 GPa and σ_f between 130 and 167 MPa. The glass showed no significant decrease of its mechanical properties after 8 weeks in SBF. The properties obtained are really promising for the use of phosphate glasses as a bone substitute in certain surgical applications.

Upon implantation bioactive glass undergoes a series of reactions that leads to the formation of a calcium phosphate-rich layer. Most in vitro studies of the changes that occur on the surface of bioactive glass have employed the use of buffer solutions with compositions reflecting the ionic composition of interstitial fluid. Although these studies have documented the physical chemical changes associated with bioactive glass immersed in aqueous media, they do not reveal the effect of serum proteins and cells which are present at the implantation site. In the present study, we document, using Atomic Force Microscopy (AFM) and Rutherford Backscattering Spectrometry (RBS), significant differences in reaction layer composition, thickness, morphology and kinetics of formation arising from the presence of serum proteins.

The data reveal that the uniform and rapid adsorption of serum proteins on the surface may serve to protect the surface from further direct interaction with the aqueous media, slowing down the transformation reactions. This finding is in agreement with previous studies that have shown that the presence of serum proteins significantly delays the formation of hydroxyapatite at the surface of bioactive glass. These data also support the hypothesis that initial reaction layers in vivo interact with cells to produce the tissue-bioactive glass interface typically observed on ex vivo specimens.

Calcium metaphosphate (CMP) ceramic is a good candidate for a biodegradable biomaterial because of its dissolution property in biological environments. This study evaluates the degradation of CMP glasses in distilled water by measuring the weight loss according to immersion time during incubation at 37°C. In order to compare the degree of hydrolytic degradation, four type glasses were prepared; pure CMP, and CMP glasses with the addition of Na₂O, Fe₂O₃, and TiO₂ respectively. The dissolution rate of the CMP glass was increased steadily with increasing Na₂O content. However, in both cases of the glasses added TiO₂ and Fe₂O₃, respectively, the dissolution rates were gradually decreased as increasing the content of them. SEM examination shows the different degradation behaviors according to the different oxides additives. Surface morphological changes before and after degradation tests were quite different. From the results, the dissolution rate of CMP glasses can be controlled by the addition of some oxides such as Na₂O, TiO₂, and Fe₂O₃.

Porous bioactive ceramic materials can be very useful on the filling of bone defects, as scaffolds for tissue engineering, or as carrier systems for the delivery of drugs. The present work describe an innovative methodology for producing porous bioactive ceramic structures, starting from hydroxylapatite or bioactive glass-ceramic powders, that present an adequate micro and macroporosity combined with compressive mechanical properties matching those of cancellous bone. The described processing route is based on a microwave baking process using a powder containing corn starch, sodium pyrophosphate and sodium bicarbonate as blowing agent, and can be used to produce either hydroxylapatite based or glass-ceramic porous structures. By using this new methodology it was possible to produce both porous bioactive glass-ceramic and HA/TCP bi-phasic structures with adequate micro and macroporosity combined with mechanical properties that will eventually allow for their successful use in a range of biomedical applications.

Self-organized nanocomposites of hydroxyapatite (HAp) and collagen were prepared by controlling temperature and pH on the basis of a biomimetic process. Transmission electron microscopic observations indicated that the composites prepared at pH 8-9 and 40°C had the bone-like structure in which the c-axes of HAp nanocrystals aligned along collagen fibers forming bundles of about 20μm in length and 1μm in diameter. The mechanical strength of the composites obtained was dependent on the degree of self-organization: the maximum 3-point bending strength was 39.5±0.88MPa and Young’s modulus 2.50±0.38GPa. When implanted in Wister rats’ craniums and beagles’ bilateral radii, osteoblasts and osteoclasts were induced near the composites after two weeks, and the composites were covered with a newly formed bone after 12 weeks.

Hydroxyapatite (HA) reinforced high density polyethylene (HDPE) composites (HAPEX™) have been developed as a bone analogue for medical applications. Conventionally processed HAPEX^TM containing 40vol% of HA possesses a stiffness approaching the lower bound of human cortical bone and is now used in minor- or non- load bearing areas in patients. In order to improve the mechanical properties of HAPEX™ and hence extend its application into major load bearing areas, HAPEX™ with various amounts of HA was hydrostatically extruded at different extrusion ratios. The extruded rods were subsequently tested under tension or bending. Their structure as well as fracture surfaces were examined under an SEM. The molecular mass of the HDPE matrix was analyzed at each processing stage. DSC thermograms were also obtained to study the effects of hydrostatic extrusion. It was found that the uniform distribution of HA in the HDPE matrix achieved by compounding was not altered by hydrostatic extrusion, but the average molecular weight of HDPE was reduced. DSC results indicated polymer chain alignment along the extrusion direction. Mechanical properties of HDPE and HAPEX™ were substantially increased by hydrostatic extrusion. It was evident that the higher the extrusion ratio, the stronger and the stiffer the HAPEX™ rod. Hydrostatically extruded HAPEX™ containing 40vol% of HA possessed a Young’s modulus of 11.4GPa and fracture strength of 91.2MPa, which are within the bounds for mechanical properties of human cortical bone. This clearly shows the potential of HAPEX™ for major load bearing applications.

A variety of bioactive particle filled polymers have been developed for tissue replacement since the early 1980s. In this investigation, hydroxyapatite (HA) reinforced polysulfone (PSU) composites were produced and evaluated for potential medical applications. Composites containing up to 15vol% of HA were studied at the preliminary stage. The HA/PSU composites were made through a standardised procedure by incorporating a commercially available HA powder into a polysulfone resin of medium viscosity that is suitable for injection moulding. Compounded materials and injection moulded parts were assessed using a variety of techniques. It was found that HA particles were well dispersed in the PSU matrix after the compounding process. Defect-free composite samples could be obtained by injection moulding. Thermogravimetric analysis (TGA) verified volume percentages of HA in the composites. Differential scanning calorimetry (DSC) results indicated that the glass transition temperature (Tg) of the polymer matrix was not affected by the incorporation of HA. It was shown through dynamic mechanical analysis (DMA) that the storage modulus of the composite was increased with an increase in HA content below ~185°C which is Tg of the polymer, while tan δ was maintain at nearly the same level for all composites. It was established that water uptake reached an equilibrium after 7 days’ immersion in distilled water for all composites and unfilled PSU. It was found that after 7 days’ immersion in distilled water, the storage modulus of HA/PSU composite was decreased less than that of unfilled PSU.

This study evaluated the possibility of obtaining bioactive coatings on polyethylene/bioactive glass composites exhibiting a very good mechanical performance. High molecular weight polyethylene (HMWPE) was reinforced with 10 to 40% (wt.) of a bioactive glass (BGE1) and a glass-ceramic (BGE1C), in the SiO₂-3CaOP₂O₅-MgO system. The composites were compounded by twin-screw extrusion (TSE) and then injection moulded into dumb-bell tensile samples. The composites presenting adequate mechanical properties were then coated with a bioactive layer by two methodologies: (i) an adapted biomimetic route using a similar glass as a precursor of calcium-phosphate (Ca-P) film deposition, and (ii) the production of a ‘sandwich’ with bioactive glass particles, previously mixed with UHMWPE powders, made to adhere to both faces of tensile samples by compression moulding. The obtained results indicated that it is possible to produce composites presenting a modulus of 11.2 GPa coupled with a tensile strength of around 117 MPa. The developed composites could be coated with a Ca-P layer by an adapted biomimetic route. Furthemore, the ‘sandwich’ route allowed for the production of load-bearing composites, presenting a highly bioactive surface, which strongly adheres to the HMWPE matrix composites.

Elastic moduli, (n=3) for eight composite systems were determined using an ultrasonic method. Mean values for glass composite ranged from 14.81 ± 0.14 GPa for silane treated filler to 10.84 ± 0.35 GPa for non-silane treated material. Mean value for Young’s modulus of low temperature fired inorganic silane treated filler was 11.96 ± 0.05 GPa. Using a Kokubo biomimetic method the eight composite substrates were also evaluated to determine their ability to deposit calcium, phosphorus and sodium on their surface when stored in a dynamic 1.0 concentration of SBF solution for 30 days @ 37°C. Single glass and low temperature fired inorganic constituent of same composition (SiO₂-CaO-Na₂O-P₂O₅) were used, combined in two different dimethacrylate resin matrix polymers. Fillers were introduced with and without silane treatment. Deposits of Ca and P were observed for composite systems. Strong correlation was found between deposition of Ca and P for each substrate (p<0.001). Data indicate that significant proportions of deposition came from SBF solution. Elastic moduli showed a significant effect for the use of silane treatment, as well as between glass and the same low-temperature fired inorganic formulation (p=0.05).

An investigation was performed with the objective of determining the effects of adding calcium-phosphate based materials of varying Ca:P ratios on the sintering characteristics and phase composition of hydroxyapatite. Samples were prepared from a commercially available hydroxyapatite (Plasma Biotal, U.K.) and two Ca-P additives, CAP1 and CAP2. Compacts were then pressed and sintered at 1300°C for 2 hours and characterised by measurements of linear shrinkage, density, and X-ray diffraction. The results were compared with those for pressed and sintered hydroxyapatite, which served as a control. The CAP2-HA underwent a greater degree of shrinkage and densification than both CAP1-HA and as-received HA, demonstrating its potential as a sintering aid. Furthermore, X-ray diffraction patterns demonstrated that there was minimal decomposition of the HA to TCP in the CAP2-HA than in the CAP1-HA, and preliminary strength tests indicated that the CAP2 additions reinforced the HA.

Three groups of bioactive composite (designated AWC, HAC and TCPC) each consisting of bisphenol-α-glycidyl methacrylate (Bis-GMA)-based monomers and a bioactive filler of either AW glass-ceramic (AW-GC), hydroxyapatite (HA) or β -tricalcium phosphate (β -TCP) powder were made in order to evaluate the influence of a kind of bioactive filler and its content on mechanical properties and osteoconductivity of the composite. The proportion of each filler added to the composite was 50, 70, and 80% (w/w). Nine types of sample were subjected to the mechanical testing. The compressive and bending strengths of AWC were higher than HAC and TCPC in each filler content. The composites were evaluated in vivo by packing them into the intramedullary canals of rat tibiae. To compare osteoconductivity of the composites, an affinity index was calculated. AWC showed higher affinity index than HAC and TCPC in each filler content. Results suggest that that higher osteoconductivity of AWC were due to higher reactivity of AW-GC powder on the composite surface. AWC shows promise as a basis for developing highly bioactive and mechanically strong composite materials.

In vitro and in vivo biological performance of a P₂O₅-CaO-CaF₂ glass reinforced hydroxyapatite, GR-HA, and sintered hydroxyapatite, HA, were assessed. In vitro evaluation using MG63 osteoblast-like cells showed that GR-HA composites caused a delay in cell proliferation and a reduction OC expression compared to HA. Total DNA results were also affected. This in vitro biological behaviour may be explained in terms of different surface characteristics of GR-HA, namely higher dissolution rate than HA, more negative surface charge and higher hydrophobicity, as determined by zeta potential and wettability measurements. However, in vivo results obtained from push-out testing of implanted cylinders in the tibiae of Japanese rabbits clearly indicate that GR-HA composite is more osteoconductive than sintered HA. The in vivo response is discussed in terms of the presence of β and α-TCP phases in the microstructure of the GR-HA composite.

The mechanical inadequacies of calcium phosphates, such as hydroxyapatite (HA), for load bearing medical implant applications has been extensively documented. Conversely, poly(etheretherketone) (PEEK) is a semi-crystalline polymer with excellent mechanical properties, high chemical resistance and good thermal stability. Hence, composite formulations combining the properties of PEEK with the bioactivity of HA, may have potential for use in load bearing implants. However, since the utilisation of such systems requires processing at relatively high temperatures (≈ 400°C), it is important that any changes to the polymer that might be caused by the presence of the bioceramic component be fully understood.

In this study, the thermal stability of a series of precursor PEEK/HA composite mixtures has been investigated by conventional and modulated DSC methods. In addition, the materials of interest have been characterised by FTIR, XRD and high resolution XPS, as a function of temperature. Modulated DSC has provided an accurate means of determining the effect of the bioceramic phase on PEEK crystallinity. This is due to the ability of the technique to provide an accurate measure of the polymer glass transition (T_g) and crystallisation (T_c) temperatures. From these data it has been possible to show that the presence of HA, even at compositions comprising ≈ 90 % wgt/wgt HA, does not adversely effect the % crystallinity of the PEEK over the DSC temperature range. These findings are supported by the chemical and structural analyses, which indicate no significant adverse effects on the PEEK from the presence of HA.

Hydroxyapatite is the well known bioactive ceramic used in medical and dental fields as blocks and particles, while chondroitin-sulfate is a dominant polysaccharide component of cartilage. Novel composite materials consisting of hydroxyapatite [Ca₁₀(PO₄)₆(OH)₂] and chondroitin-sulfate were synthesized by a coprecipitation method with a H₃PO₄ solution and a Ca(OH)₂ suspension, one of which contain chondroitin-sulfate, and were consolidated under a cold isostatic pressure. The composites were evaluated by X-ray diffractometry, Fourier transformed infrared spectroscopy and transmission electron microscopy. In the composites, hydroxyapatite nanocrystals contained calcium-deficiency and a small amount of carbonate ions like human bone minerals and their c-axes were aligned along chondroitin-sulfate molecules by a self-assembly mechanism.

A composite, composed of biphasic calcium phosphate, BCP (60% hydroxyapatite, HA + 40% β-tricalcium phosphate, β-TCP) granules and a hydrophilic polymer (hydroxy-propyl-methyl cellulose, HPMC) was developed as an injectable bone substitute (IBS). The composite was prepared by incubating for 6 and 12 months a mixture of 60% BCP powder (w/w) and 40% HPMC. The composite was then steam sterilized and non-sterilized composite served as control. The interaction between ceramic crystals and polymer and the effect of sterilization were investigated using scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HrTEM). Results: SEM demonstrated the degradation of ceramic in the composite after incubation. HrTEM demonstrated the presence of a dissolution zone, about 13 nm, associted with the HA crystal surfaces. Precipitated globular microcrystals (2-3 nm in diameter) represented the first zone of interaction between HA crystals and the polymer. Under this zone, the inter-reticular distances of HA lattice planes appeared enlarged by 1.2% [from 0.817 to 0.827 nm for (100) lattice planes]. The enlargement of lattice planes could be due to HPO₄ incorporation in the newly formed apatite crystal lattice. In β-TCP crystals, dissolution took place on several nanometers. Conclusion: This study demonstrated that interaction between hydrophilic polymer and calcium phosphate ceramic occurs only on very thin layer (several nanometers).

Ceramic-polymer composite biomaterials were prepared by hot-pressing a mixture consisting of poly-L-lactic acid (PLA) and hydroxyapatite fibers (HAF). HAF can be prepared successfully by heating a compact consisting of β-calcium metaphosphate fibers (CPF) with Ca(OH)₂ particles in air at 1000 °C and subsequently treating the resultant compact with dilute aqueous HCl solution. HAF was 40 ~ 150 μm in length and 2 ~ 10 μm in diameter; HAF has almost the same dimensions as those of CPF. After PLA dissolved with methylene chloride was mixed with the fibers, the mixture was dried completely and subsequently it was hot-pressed uniaxially under a pressure of 40 MPa at 180 °C, resulting in fabrication of the PLA/HAF composite. The modulus of elasticity was improved effectively even by introducing a small amount of HAF; almost no degradation in the bending strength was observed and the modulus of elasticity showed high values of 5 ~ 10 GPa when the fibers of 20 ~ 60 wt.% were introduced. The stress-strain curves in the bending test of the PLA/HAF composites showed that very high energy is consumed for their fracture.

The effects of TiO₂ content and heat treatment on the bioactivity and mechanical behavior of polydimethyl-siloxane(PDMS)-modified CaO-SiO₂-TiO₂ hybrid materials were investigated. Samples were prepared by hydrolysis and polycondensation of PDMS, tetraethoxysilane (TEOS), tetraisopropyltitanate (TiPT) and calcium nitrate. The samples with varying (TiPT)/(TEOS + TiPT) molar ratios from 0 to 0.30 were prepared. The apatite-forming ability in a simulated body fluid (SBF) increased with increasing TiO₂ content. The Young’s modulus and strain at failure increased and decreased, respectively, with increasing TiO₂ content. The samples with a fixed molar ratio, (TiPT)/(TEOS + TiPT) = 0.10 were heat-treated at various temperatures from 60 to 300°C for 24 h. The Young’s modulus and failure strain of the heat-treated samples increased and decreased, respectively, with increasing heat treatment temperature, but the bending strength was found to be independent of treatment temperature. Pore- and crack-free trasparent hybrids exhibiting high apatite-forming ability as well as mechanical properties analogous to those of human cancellous bone were developed. These hybrids may be used as a new kind of bioactive bone-reparing materials.

Experimental composites containing bioactive glass, glass-ceramic and bioactive low temperature fired inorganic fillers (SiO₂-CaO-P₂O₅-Na₂O) were synthesized by wet chemistry. Two chemically activated dimethacrylate matrix resins were used together with 0 or 30% low molecular weight hydrophilic monomer. Composites contained 70 or 65 (wt%) filler particles with and without silane treatment. Fracture toughness (K_Ic) (n=5) was performed on specimens following storage in either SBF or distilled water @ 37°C for 30 days. Fracture toughness discriminated between glass-ceramic, glass and low temperature inorganic filler (P< 0.001). Mean values for silane treated glass-ceramic ranged from 1.56 ± 0.41 MPa.m^0.5 to 0.4 ± 0.18 MPa.m^0.5 for the none silane treated composite. In contrast values for the glass filler were from 1.39 ± 0.27 MPa.m^0.5 for the silane treated to 0.42 ± 0.03 MPa.m^0.5 for the non-silane treated. Mean fracture toughness values for low temperature fired inorganic constituent ranged from 1.03 ± 0.19 MPa.m^0.5 for silane treated and 0.36 ± 0.28 MPa.m^0.5 for non-silane treated. No effect due to storage in SBF or distilled water was found.

Various materials have been used for knee and hip prostheses over the last few decades due to considerations for their mechanical and tribological properties and their biocompatibility. Hydroxyapatite (HA) reinforced high density polyethylene (HDPE) composites have been developed as a new generation biomaterial for skeletal applications. In this investigation, the tribological properties (i.e., wear rate, coefficient of friction, and lubrication in the presence of proteins) of HDPE and HA/HDPE composites were evaluated against duplex stainless steel under dry and lubricated conditions. Lubricants included distilled water and aqueous solutions of proteins (egg albumen or glucose). It was found that HA/HDPE composites had lower coefficients of friction than HDPE under certain conditions. Furthermore, HDPE exhibited more severe fatigue failure marks than the composites. The degradation and fatigue failure due to the presence of proteins were severe for low speed wear testing (100 rpm) as compared to high speed wear testing (200 rpm). Both egg albumen and glucose were found to be corrosive to steel and adversely reactive for HDPE and HA/HDPE composites. This was clearly shown by SEM micrographs of HDPE and HA/HDPE specimen surfaces taken after the tests. The wear modes observed were similar to that of UHMWPE. Specimens tested with egg albumen also displayed higher wear rates, which again were attributed to corrosion accelerated wear of these specimens.

Some porous hydroxyapatite ceramics were fabricated using the fibrous particles; most of the pores in these ceramics could be regarded as open pores. The methylmethacrylate monomer containing the polymerization initiator was induced into the open pores of the above porous ceramics in a chamber under reduced pressure; such introduced monomer was polymerized by heating it at 60 °C for 48 h. The SEM observation showed that the poly (methylmethacrylate) (PMMA) was present inside the porous HAp ceramics. Among the HAp-PMMA hybrid materials derived from various porous ceramics, the highest fracture toughness was 3.2 MPa•m^1/2, which was ˜ times higher than that of the dense HAp ceramics.

Since AEROSIL® is one of the reinforcement materials for silicone, we synthesized the organically modified silicate (ORMOSILS) gels reinforced with AEROSIL® starting from poly (dimethylsiloxane) (PDMS), tetraethoxysilane (TEOS) and calcium nitrate (Ca(NO₃)₂•4H₂O) through sol-gel processing. The storage modulus increased with the AEROSIL® content along with the increase in PDMS-AEROSIL® bonds. The gel of a specific composition could deposit apatite within 1 day of soaking in the Kokubo solution, since it included many calcium ions on the surface.

In the present study, hydroxyapatite (HAp) was electrophoretically deposited on Ti, Ti6A14V and 316L stainless steel substrates. The effects of sintering temperatures ranging from 875°C to 1000°C on the bonding strength between the HAp coating and metal substrates were investigated. In general, sintering causes decomposition of the HAp coating even at a temperature of 875°C. In the present study, dual HAp coatings were prepared. The use of dual HAp coatings enabled decomposition to be confined to the “undercoat”, while the surface coating remained decomposition free. The bonding strength between the HAp coating and the metal substrates was assessed by shear strength testing, according to ASTM F 1044-87. It was found that the coating on stainless steel sintered at 925°C gave the best result among the three substrates, 25 MPa of adhesive strength. The high adhesive strength of stainless steel was mainly due to the high thermal expansion coefficient of this metal. This resulted in residual compressive stresses in the coating, whereas the low thermal expansion coefficients of Ti and Ti6A14V produced residual tensile stresses. The tensile stress in the coating over Ti and Ti6A14V substrates caused the coatings to buckle and crack, thereby greatly decreasing their bonding strengths.

Bonelike polycrystalline hydroxyapatite (HAp) thin films were prepared by low temperature hydrothermal annealing from amorphous calcium phosphate films synthesized by sputtering method. The surface properties of the thin films were investigated by X-ray powder diffractometry (XRD), infrared spectroscopy (IR) and X-ray photoelectron spectroscopy (XPS). The biocompatibility was histologically evaluated by bone tissue reaction. The precursory amorphous coating were deposited on titanium with a rf-magnetron sputtering apparatus using calcium phosphate (CP) glass targets in an Ar/CO₂ gaseous atmosphere. The Ca/P ratio of deposited HAp films was controllable in a ranging from 1.50 to 1.67 by adjustment of the chemical composition for CP glass target. The polycrystalline thin films were formed by the hydrothermal post-annealing at above 140 °C. The post-annealed films were identified as carbonated calcium hydroxyapatite by XRD, IR and XPS. The CO₃^2- ions occupied the PO₄^3- site of the apatite structure. It was concluded that the bonelike HAp thin films contained CO₃^2- ions and were endowed with the outstanding biocompatibility.

Calcium phosphate bioceramics are widely used as bioactive coatings on hard tissue implants. Their presence as relatively thin films has significant advantages for the stability of the coating during the important osteoconductive phase. RF magnetron sputtering is one of the techniques favoured for the deposition of such films, due primarily, to its ability to provide a high degree of process control. Hence, the properties of the films can be manipulated, such that, the resultant chemistry and morphology engenders a favourable tissue response.

In this study, thin films have been deposited onto titanium-based substrate surfaces by RF magnetron sputtering from hydroxyapatite powder targets. The substrates used were medical grade titanium, polished Ti-6Al-4V alloy and titanium surfaces prepared by sputtering from a metal target onto freshly cleaved mica and clean glass. Selected samples were subsequently annealed in air up to 800°C. Coatings were examined by AFM and SEM and further analysed by XPS and EDX before and after HA deposition. The resultant structure and chemical composition were found to be strongly influenced by the underlying substrate morphology, with the films depositing preferentially on surface defects, where nucleation energies are relatively low. Post-deposition heat treatment increased the microstructural regularity, resulting in the formation of crystallite clusters in the range 500 nm to 2 μm. Both surface preparation and post-deposition annealing were found to significantly influence the composition of the films, with the latter treatment bringing the Ca:P ratio closer to the value for stoichiometric HA.

Process related variability on plasma sprayed HA coatings have shown significant influence on the coating characteristics. The coatings were generated from wet precipitated HA powders which were subsequently produced by the plasma spraying technique. The effects of spraying standoff distance and particle size ranges on the tensile bond strength, phase composition and microstructural characteristics of the spheroidized HA (SHA) coating were investigated. XRD and SEM analysis revealed a substantial increase in the amount of amorphous and other undesirable calcium phosphate phases in the coatings as the spray distance increases. It was found that a well-defined splat structure with a maximum adhesion strength was obtained with SHA 20˜45 μm powders using a spray distance of 10 cm at a net energy of 12 kW. The presence of microstructural defects and the amount of melting served to affect the structural integrity of the coating.

Implant failure due to inadequate bone screw fixation, particularly in the osteoporotic bone, is a frequent complication. Studies showed a significant improvement in screw stability of external fixation treatments when employing hydroxyapatite (HA) coated screws. We studied whether coating screws with osteoconductive materials could similarly improve screw stability in internal fixation. Forty-eight AO/ASIF cortical screws were divided into Group A: stainless steel; Group B: HA-coated stainless steel; and Group C: titanium (Ti)-coated Ti screws which were implanted randomly into the femurs and tibiae of six sheep. Insertion torque was 2,000 N/mm. At one and three months Group A’s extraction torque was lower than its insertion torque (p<0.001) while Group B and D’s extraction torque was higher than their insertion torque (p<0.001). Screws coated with osteoconductive materials provided higher stability than standard screws and should be used to improve fixation stability and reduce postoperative complications caused by screw instability.

Our aim was to evaluate the mechanical bone anchorage of TiO₂- gritblasted titanium implants as received (Ti) or provided with a calciumphosphate (Ca-P) coating of 0.1μm (CaP-0.1), 1μm (CaP-1 ), or 4μm (CaP-4) thickness. The implants were inserted in the femoral condyle of 12 goats. After 6 and 12 weeks, interface strength and appearance was evaluated using torque testing and scanning electron microscopy (SEM). Alreday at 6 weeks, all implants resisted very high torsional failure forces (Ti=117 Nm, CaP-0.1=142 Nm, CaP-1=154 Nm, and CaP-4=150 Nm). Although, CaP coated implants showed higher torque failure loads than noncoated implants, no statistical difference existed. The 12 week data (Ti=154 Nm, CaP-0.1=159 Nm, CaP-1=140 Nm, and CaP-4=171 Nm) demonstrated again no significant differences. Nevertheless, SEM showed that CaP-coated implants conducted more bone growth into the screwthreads. The fracture plane for CaP-4 implants was situated at the coating-implant interface or inside the coating. For CaP-0.1, CaP-1, and Ti implants, torque testing tesulted in failure at the bone-implant interface. Therefore, we conclude that all implants resulted in a good bone bonding strength. The Ca-P coatings showed no negative initial effect, but seemed to improve the bone fixation.

The aim of this study was to evaluate the in-vivo behavior of calcium phosphate magnetron sputtered coatings applied to roughened implants. RF magnetron sputter deposition was used to produce 0.1, 1.0 and 4.0 μm thick Ca-P coatings on TiO₂ grit-blasted titanium discs. Of each group, half of the coated specimens were subjected to an additional infrared heat treatment for 30 sec at 425-475°C. Annealing of the 4 μm thick coatings resulted in the appearance of a few cracks. Subsequently, the discs were implanted subcutaneous into the back of rabbits. After 1, 4, 8 and 12 weeks of implantation, the implants were retrieved and subjected to histological and physicochemical evaluation. Histological evaluation revealed that the tissue respons to all coated implants were very uniform. All implants were surrounded by a very thin connective tissue capsule. The capsule was usually free of inflammatory cells. At the interface, there was a close contact between the capsule and implant surface and no inflammatory cells were seen. Physicochemical evaluation showed that all the amorphous coatings had disappeared within 8 weeks of implantation. Further, at all implantation periods the heat-treated 1 and 4 μm thick coatings could be detected. In addition to this a granular precipitate was deposited on the heat-treated 4 μm thick coating.

On basis of our findings, we conclude that 1 μm thick heat-treated Ca-P sputter coating on roughened titanium implants appear to be of sufficient thickness to show bioactive properties, under in-vivo conditions, while the titanium surface roughened by gritt-blasting has a greater resistance to delamination.

In this work full density alumina substrates have been coated by a bioactive calcium-fluoro-phosphate glass (RKKP). In order to avoid high stresses at the interface between the substrate and the coating, due to the remarkable difference between the thermal expansion coefficients of alumina and of this bioactive glass, some layered structures have been prepared by using glasses of different composition and different thermal coefficients as intermediate layer between alumina and RKKP. The further advantage of this method is the good control of alumina diffusion from the substrate to the glass coating, which can affect the bioactivity of the glass by changing its composition.

The interface between the coatings and the substrates have been characterised by means of optical and Scanning Electron Microscopy (SEM), and by compositional analyses by Energy Dispersive Spectroscopy (EDS). The glass layers are well bonded to the substrate and few alumina still diffuses into these layers. Vickers Indentation and X-Ray Diffraction analyses (XRD) are in progress in order to evaluate the adhesion of the coatings to the substrate and to investigate their microstructure.

To improve hydroxapatite (HA) coatings on the titanium substrate, HA/Ti composite was formed on substrates using Radio-frequency (RF) plasma spraying process, as this composite layer may reduce the residual stress due to the large difference in the liner thermal expansion coefficient between the substrate and HA. HA/Ti composite was prepared by controlled feeding of HA and Ti powder, as the composition of coatings becomes HA-rich toward the outmost. Coating layer was evaluated by SEM-EDX, XRD and tensile testing. Orientation in c-axis direction of prepared coatings was observed from X-ray diffraction patterns. HA/Ti composite coating gave a higher adhesive (tensile) strength over 10 MPa than direct HA coatings on substrate.

In this paper, we report that a thin film of hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂), or HA was deposited by means of laser ablation to increase the biological compatibility of a titanium alloy(Ti-6A1-4V). Polished substrates with different microstructures (0.1 ˜ 3.0, μ mRmax) were prepared. Depositions were carried out in a water vapor by bubbling O₂ gas through a water bath at 0.1Torr(1.3 × 10^-2 Pa). An ArF excimer laser operating at a repetition rate of 10Hz was used for deposition. The substrate temperature was varied from 500°C to 560°C. The crystal structures of HA film were evaluated by X-ray diffractometry (XRD). At temperatures lower than 500°C, the films were amorphous. At temperatures greater than 560°C, the films had crystalline α - tricalciumphosphate (α -TCP). The crystallized HA was obtained at about 530°C. The surface morphology of the HA film was observed using an atomic-force microscopy (AFM). The mechanical properties of the film were measured by the scratch test and the peeling off test by means of a tensile-test machine. In the peeling off test, the adhesive strengths between HA films and the substrates were about 2.3 and 5.4MPa for surface roughness 0.1 and 1.0 μ mRmax,respectively.

Biodegradable calcium metaphosphate (CMP) sol was prepared and then coated on Ti6A14V substrates by spin-coating technique. In order to investigate the effect of hydrolysis time of (OC₂H₅)₃P on the reaction with Ca(NO₃)₂4H₂O, the P-precursor was pre-hydrolyzed for 1, 5, and 10 hours before the reaction with the Ca-precursor. At least above 5 hours of pre-hydrolysis of P-precursor were required to obtain β -CMP. The CMP coated specimens were dried at 70, 100, and 130°C, respectively and then heat-treated at 630°C for 3 hours with and without holding at 476°C for 2 hours. It has been found that the drying temperature of the CMP coated specimens was one of the most important factors affecting the homogeneity of the coating layer. The optimum drying temperature was 70°C, and the CMP coated layer with holding at 476°C during firing was homogeneous and had fewer cracks, compared with that of sample without holding.

Bioactive glasses promise several advantages in orthopaedic applications, in particular as coating material of metallic substrates. The bioactivity of the glasses is linked to their capability of producing an intense effect on bone tissue through the formation of a surface reaction layer. In this work the AP40 bioactive glass-ceramic was deposited by plasma spray on sand-blasted Ti-6A1-4V substrates. In order to investigate the bone-bonding mechanism of this glassy material, a study of the surface structural changes of the deposited layer after exposure to simulated body fluid (SBF) is reported.

A series of instrumental investigations were carried out on the powders of the biological glass, on the deposited layers and on the coatings after 5, 20, 25 and 30 days of immersion in SBF. X-ray diffraction (XRD) both in thin film (GID) and in Bragg-Brentano (θ-2θ) configuration, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were utilised mainly to verify the crystallographic and compositional transformations with time. θ-2θ XRD spectra show that the glassy layer contains a crystalline phase of hydroxylapatite, which increases after the immersion in the physiological media. At the same time the GID analyses showed a reduction of the thickness of the coating.

We evaluated bone-bonding strength of bioactive bone cements (AWC and HAC). AWC consisted of AW-GC powder and bisphenol-α-glycidyl metacrylate (Bis-GMA)-based resin and HAC consisted of hyodroxYapatite powder and the same resin of AWC. The proportion of powder added to each cement was 70% w/w. In order to compare the failure load, cement plates which had an uncured surface on one side and a cured surface on the other were made. HAC plates were also made in the same way as AWC plates. One of the plates was soon implanted into the proximal metaphysis of the tibiae of a male Japanese white rabbit so as not to damage the surface properties, and the load was measured by a detaching test 8 weeks after implantation. The failure load for AWC on its uncured surface (2.05 ± 1.11 kgf, n=8) was significantly (p<0.0001) higher than that for AWC on its cured surface (0.28 ± 0.64 kgf, n=8). The load for HAC on its uncured surface (1.40 ± 0.68 kgf, n=8) was significantly (p<0.0006) higher than that on its cured surface (0.00 ± 0.00 kgf, n=8). There was no significant difference between the load for AWC and that for HAC on their uncured surfaces (p=0.086) and on their cured surfaces (p=0.45) although the value for AWC was higher than that for HAC. The reason is that surface roughness for HAC is larger than that for AWC. Therefore, mechanical interlocking may be more effective for HAC compared with AWC. Histologically direct bone formation was observed both AWC and HAC on their uncured surfaces and Ca-P-rich layer was observed only on the uncured surface of AWC. We concluded that the uncured surface was useful for exposing bioactive powder on the surface of the cement and effective for inducing bone-bonding.

Polymethylmethacrylate (PMMA) bone cement, which has been widely used in total hip arthroplasty (THA), has several problems. To improve these problems, the authors have developed new bioactive bone cement, which has a capability of bonding directly with bone, and has greater mechanical strength than PMMA bone cement. In this study, THAs were performed in dogs using bioactive bone cement (BABC) consisting of AW glass-ceramic powder and SiO₂ powder as the filler and bisphenol-a-glycidyl dimethacrylate (Bis-GMA) based resin as the organic matrix, and the outcomes were compared with the results of PMMA bone cement. Previously, we reported on a higher bonding strength and higher Affinity index of BABC to bone in dogs’ femora for up to 24 months. In the present study, femoral bone resorption was observed at 24 months after implantation in the BABC group, although it was not observed in the PMMA bone cement group. Resorption rate of the BABC group calculated by digitizer using SEM images of cross section of the femur was 4.4±4.4 % and 10.1 ± 4.1 % at 12 months and 24 months, respectively, whereas that of PMMA group was 1.3±1.9 % and 1.5±0.7 % at 12 months and 24 months, respectively. There was a significant difference between both groups at 24 months.

A comparative study between three α-TCP based bone cements has been performed. The study has been focused on the reactivity of the cements in order to know the effect of several processing factors on their kinetic behaviour. The hardening curves and the extent of conversion of α-TCP into a calcium deficient apatite precipitate have been obtained as a function of the hardening time. The factors studied have been the particle size of the α-TCP main reactive phase and the addition of calcium carbonate as a modifying setting additive.

The results showed a strong correlation between the hardening curve and the hydration rate of the main reactive α-TCP phase. However, the results obtained for the cements were statistically different between them. A significant decrease of the particle size of α-TCP was found to accelerate the setting and the hardening of the cement. An increase of the amount of calcium carbonate in the initial powder mixture was shown to decrease the rate of hardening with an important decrease of the compressive strength at saturation.

New calcium phosphate cement has been developed. The powder component is a mixture of α-tricalcium phosphate, tetracalcium phosphate and calcium hydrogen phosphate dihydrate, while the liquid is an aqueous solution containing sodium succinate and sodium chondroitin sulfate. An injectable paste or a hand-shapeable dough can be prepared by manually mixing the two components for a minute with proper powder to liquid ratio (P/L=2.0-4.5). The mixture can mostly set within about 6 minutes after mixing at 37°C in humid atmosphere, although the setting time is dependent on the P/L and the environmental temperature during the mixing process. The mixture also sets in the simulated body fluid without severe change in pH and gradually turns into low crystalline carbonated hydroxyapatite that can be slowly substituted by bone in vivo. Compressive strength of the cured material is about 65MPa in 3 days after mixing, and reaches its final strength more than 70MPa in a week. Elastic modulus of the hardened body is about 4.5GPa. This is slightly higher than porous hydroxyapatite implants. These strength and biocompatibility as well as less invasive surgical process by injection of this new cement will bring many opportunities to be applied at fracture fixation, filling bone defect and intensification of bone.

We have developed a bioactive bone cement (BABC) which consists of apatite and wollastonite containing glass-ceramic (AW-GC) powder and bisphenol-A-glycidyl dimethacrylate (Bis-GMA)-based resin. In the present study, the effectiveness of the BABC for repair of segmental bone defects under load-bearing conditions was examined using a rabbit-tibia model. Polymethylmethacrylate (PMMA) bone cement was used as a control. A 15-mm-length of bone was resected from the middle of the shaft of the tibia, and the tibia was fixed by two Kirschner wires. The defects were replaced by cement. Each cement was used in 12 rabbits, with six rabbits each being killed at 12 and 25 weeks after surgery and the tibia containing the bone cement was excised and tension-tested. At both the intervals studied, the failure loads of the BABC were significantly higher than those of the PMMA cement. There was no significant change between the failure loads at 12 and 25 weeks for either cement. The BABC was in direct contact with bone, whereas soft tissue was observed between cement and bone in all PMMA cement specimens. Results indicated that the BABC was useful as a bone substitute under load-bearing conditions.

Bioactive ceramics have bone conductivity. We report the observation on the histological and the chemical changes of calcium phosphate cement(CPC) to be implanted into the femur of mature rabbits. Osteoid formation was observed in the surrounding of the CPC at one week after CPC implantation. New bone formation with the small blood vessels was observed at three weeks. CPC conducts the new bone formation with three layers of collagen fibers, new bone and apatite with protein, as well as the blood vessel extension. CPC is transformed into type B carbonate apatite due to a non-cellular process, which is related to the new bone formation.

In our previous study, it was demonstrated that a newly developed bioactive bone cement, hydroxyapatite composite resin (CAP), had the ability to make a direct contact with bone having a superior mechanical proprieties in contrast with PMMA cement. The objective of this study is to evaluate the loosening mechanism of the femoral stem on using CAP cement and PMMA cement as a component of total hip replacement (THR). The simulated THR model was prepared by using Sawbone, which is made of epoxy resin composite. After cyclic loading of 1.9 KN on head of prosthesis, the strain condition of femur was measured by using a resistance strain gauge. The strain in the middle position of femur in lateral side and medial side decreases with increasing cycle numbers, especially when PMMA cement was used as a components of THR. Extensive debonding area at the stem-cement interface was observed in THR when PMMA cement was used. Whereas in CAP cement, the debonding area at the interface was less conspicuous. From these results in vitro, we can conclude that CAP cement has much higher possibility to prevent the loosening than PMMA cement.

We have prepared bone cements of calcium phosphate/mono(methacryloyloxyethyl) acid phosphate (P-1M) composite and investigated their physicochemical and mechanical properties. Calcium phosphate used in this study is as follows ; α - and β -tricalcium phosphate ( α - and β -TCP), and hydroxyapatite (HAp). When the ratio (wt %) of P-1M to each calcium phosphate was 1/2, mixture was paste-like due to the high viscosity of P-1M, and then it hardened after 30 min. The compressive strength was 26 ∼ 31 MPa for α -TCP/P-1M composite, 20 ∼ 22 MPa for β -TCP/P-1M composite, and 19 ∼ 21 MPa for HAp-200/P-1M composite. It decreased to 3 ∼ 8 MPa by heating α -TCP/P-1M and HAp-200P-1M composite at 300 ∼ 600 °C because they became to be porous. But, it was almost constant for β -TCP/P-1M composite. After α -TCP/P-1M composite was soaked in 0.9% NaCl aqueous solution for 24 hours, the surface (thickness: ∼ 0.3 mm) of the block specimen changed to calcium hydrogen phosphate dihydrate (DCPD) from α -TCP, and the inside had different structure from the surface. The shape of the surface material was rectangular plate and the inside material formed network.

We reported previously that a bioactive PMMA-based cement was obtained by using a dry method of silanation of AW-GC particles, and using high molecular weight PMMA beads. In this report, commercial PMMA bone cements (CMW1, Surgical Simplex) containing AW-GC filler in the ratio of 70wt% were investigated (abbreviated as B-CMW1 and B-Surg Simp). Their handling properties were similar to the commercial CMW1 cement that does not contain bioactrve powder (C-CMW1) as dough and setting times were 3 and 8 minutes respectively for both types of bioactive cements compared to 2 and 6 minutes respectively for C-CMW1. Bending strength of plates made from both bioactive cements and C-CMW1 cement was 90 ± 7 MPa for B-CMW1 and 98 ± 7 MPa for B-Surg Simp compared to 92±6 MPa for C-CMW1 after one day of immersion in simulated body fluid (SBF). These cements were also implanted in the medullary canals of rat tibiae. After 4 and 8 weeks of implantation, the bone-cement interface was examined using scanning electron microscope and Giemsa surface staining and the affinity index was calculated. After 8 weeks it was 55.5±10.8 for B-CMW1 and 49.4 ± 4.6 for B-Surg Simp compared to 2.0±1.4 for C-CMW1 indicating higher bioacivity than that previously reported.

An attempt to prepare the highly blood compatible titania through sol-gel processing starting from tetraethyl orthotitanate has been carried out. It is considered that the programming rate of the heating temperature is the important factor to obtain the highly blood compatible titania by observing the changes in the blood compatibility after heating at various temperatures. Then, a new method was proposed to present the anti-clotting properties of the adsorbents by the colorimetry.

Radiotherapy is one of the effective treatments of cancers. External irradiation, however, often causes damages to healthy tissues. It has been reported that 17Y₂O₃-19Al₂O₃-64SiO₂ (mol%) glass microspheres 20-30 μm in diameter are useful for in situ irradiation of cancers. This glass microsphere is already clinically used for treatment of liver cancer in Canada etc. The number of yttrium ions present in this glass microsphere is, however, not very large. In the present study, pure Y₂O₃ microspheres with smooth spherical shape 20-30 μm in diameter were successfully obtained by the inductively thermal plasma melting technique. They were essentially composed of crystalline Y₂O₃ particles. They little released yttrium into water at 95°C for 7 d, but a large amount of it into pH 4-buffered solution. After they were coated with SiO₂ film by plasma chemical vapor deposition (CVD) method, they hardly released yttrium into the pH 4-buffered solution as well as into the water. The SiO₂-coated Y₂O₃ microspheres showing high chemical durability even in the low pH environment are believed to be more effective for cancer treatment than the Y₂O₃-Al₂O₃-SiO₂ glass microspheres.

The historically and sequentially huge outbreaks of food poisoning caused by enterohaemorrhagic E. coli O157:H7 had occurred in Japan 1996, and a number of patients was estimated over 12,000 including 12 death cases. Under these situations, we initiated the work of development of the anti-bacteria ceramics, and attained our initial purpose. The core portion of ceramics, which was constituted with complex of Al, Ti and Si, was coated with silver by firing, and the final product developed was a porous material. After repeating experiments by changing mixing amount of compounds, and firing conditions, the effective ceramics against bacteria was obtained. The ceramics at 1-2% (w/v) showed the bacteria killing activity against O157 at 10⁶-10⁷ cfu/ml in water within 1hr treatment at 37°C. Similar activity was demonstrated against other types of pathogenic bacteria such as MRSA, Vibrio spp., Legionella spp. and Salmonella spp. under the same treatment conditions. The amount of heavy metals solubilized into the ceramics water was measured, however Pb was not detectable, and Zn, Cu, Ag and organic compounds were at legally allowed levels respectively. Additionally the ceramics water at 20% (w/v) solution was orally administered into rats to examine the acute toxicity, and no toxicity was convinced in animal test. From these results it is conclusively speculated that the anti-bacteria ceramics developed is the effective agent to eradicate pathogenic bacteria caused food poisonings.

Recently, it has been reported that α-tricalcium phosphate (α-TCP) dental cements containing antibiotics can make good results when used over carious dentine. However, the release behavior of antibiotics and Ca from the cement is not clarified. Therefore, the aim of this study is to examine the in vitro release profile of the antibiotic-containing α-TCP cements. Three kinds of antibiotics (Metronidazole, Cefaclor and Ciprofloxacin) were added to two commercially available α-TCP cements. The set cements were immersed in water at 37°C and the released antibiotics and Ca were determined at regular intervals until three months. The release profile of the antibiotic-containing α-TCP cements was depended on the antibiotics added. The release rate of Ciprofloxacin was not so high in the early stage but it tended to elute continuously for three months, though the release of Metronidazole and Cefaclor reached plateaus within one month. The release rates of Ca from the antibiotic-containing α-TCP cements were higher than that from the control. The amounts of Ca released from Type II were higher than that from Type I. These differences in the release profile between Type I and II cements seemed to reflect the setting reaction of these cements.

Zinc was doped into β-tricalcium phosphate up to 10 mol %. The zinc-doped tricalcium phosphate (ZnTCP), tricalcium phosphate (TCP) and hydroxyapatite (HAP) powders were mixed with a total metal-per-phosphate ratio fixed at 1.60, followed by being sintered into a dense body at 1100°C for 1 hour to make a ZnTCP and HAP composite ceramic (ZnTCP/HAP). The ZnTCP/HAP released calcium, phosphate and zinc ions for at least 30 days in a physiological saline solution.

No inhibitory effect of ZnTCP/HAP on the proliferation of MC3T3-E1 cells was observed up to a zinc content of 1.26 wt%. A relative cell growth rate increased significantly in a zinc content of the ZnTCP/HAP from 0.6 to 1.26 wt%. The ZnTCP and the ZnTCP/HAP ceramics were implanted in the femora of New Zealand White rabbits for four weeks. Histological and histomorphometrical investigation on the undecalcified sections revealed that the bone formation area per area of medullary cavity increased by 51 % (p=0.509, n=6) around the ZnTCP/HAP implants with a zinc content of 0.316 wt%, compared with the control.

Tricalcium phosphate containing Zn (ZnTCP; 0.63, 6.17 and 12.05 Zn w/w%) were investigated Zn²⁺ release from ZnTCP. The in-vitro release rates from Zn-TCP powders were measured in 25 ml of SBF containing 10 mg/100mL Ca²⁺(SBF (H)), SBF containing 5 mg/100mL Ca²⁺ (SBF(L)) or SBF without Ca²⁺ (SBF(-)) at pH7.25, 37.0+0.1°C. The Zn²⁺ release rate from 6 and 12 % ZnTCP were much faster than that at the latter stage. The Zn²⁺ release rate from ZnTCP decreased with increasing Ca²⁺ concentration in dissolution media. The rate from ZnTCP increased with increasing Zn²⁺ concentration in TCP. On the other hand, the aqueous ZnTCP suspension containing 10mg of 6 and 12% ZnTCP was subcutaneously injected into the backs of the ovarictomized female Wistar rats. The plasma Zn²⁺ levels at 1-5 days of ZnTCP loaded rats increased comparing with the control disease model. The area under the curve of Zn release profiles (AUC) of 6 and 12%ZnTCP were significantly higher than that of control disease model.

Implants (hemitrochlea) were prepared from nacre (mother of pearl) and implanted in the knees of sheep. Cartilage formed at the endoarticular surfaces of the implant, and new endochondral bone was also formed at the interface between the host cancellous bone and nacre. These phenomena resulted in the total integration of the implant.

Bioglass^® implants were used successfully in many applications. There is still a lack of information about the reaction after implantation when the surface of such soluble implants is increased, e.g. in the case of particles. In the present investigation three different types of Bioglass^® particles were tested at 7, 28, and 84 days after implantation into trabecular bone using light microscopy and histomorphometry. All three types showed bone bonding. In the case of 45s5 and 52s the bone was deposited on the implant surface, in 55s the bone formation began in between particles and reached the surface later. Bone reached the center of the defect, which was created operatively, from the periphery. The degradation of particles was high in case of 45s5, lower in 52s and lowest in 55s beginning also in the periphery of the hole. Multinuclear giant cells (MNGC) were observed in soft tissue areas in all of the implants tested. After 84 days higher numbers of MNGC were found at the surface of all bioglass particles preferentially at ventral sites. This area showed the lowest bone formation rate. The tissue response may therefore depend on the local conditions.

A bioactive graded surface structure of an amorphous sodium titanate which was free of alloying species of Mo, Zr and Al was formed on Ti-15Mo-5Zr-3A1 alloy by NaOH and heat treatments. The sodium titanate transformed into a hydrated titania via Na⁺ ion exchange with H₃O⁺ ion to induce bonelike apatite formation on the alloy substrate in a simulated body fluid (SBF). The alloying species neither released into SBF nor affected the apatite formation. Thus-formed apatite was integrated with the alloy substrate by graded structure where the apatite on top surface gradually changed into alloy substrate through hydrated titania and titanium oxide. This graded structure provides a strong interfacial bonding strength between the apatite layer and the alloy substrate.

Titanium and some of its alloys are commonly accepted as materials for orthopedic implants such as artificial tooth roots mainly due to its superior mechanical strength. Bone formation around titanium implants can make a contribution to long-term stable fixation of the implants. Therefore, enhancement of osteoconductivity of the surface of the implants has been a key to improve the implant. We are attempting to improve the fixation of the titanium implants to bone by implanting hydroxyapatite (HAP) spots on the implant’s surface. The spherical HAP ceramics were pressed against the surface of pure titanium substrate by a loading rate of 0.1 kN/min up to 1 kN at 850°C. By this method, most part, except near surface, of the spherical HAP ceramics was surrounded by deformed titanium, resulting in mechanical holding of the spherical HAP ceramics. The HAP spots on the titanium surface are expected to bond to bone much faster than titanium. Furthermore, cavities made by the implantation have sufficient volume to induce bone ingrowth that contributes long-time stability of the implants by microanchoring.

The evaluation of the historically decreasing wear data for ceramic on ceramic and metal on metal combinations is mostly restricted to quantitative measuring methods describing material loss with increasing limitations. For example an about factor 10 improvement for a current quality of a hot isostatically pressed alumina compared to earlier non-hipped alumina materials can be derived from estimations of profilomertical and gravimertical wear data in laboratory tests. Just after the first million of cycles in the joint simulator the detection limits of these methods result “no measurable wear”. In contrast, SEM and EDX show still distinct wear phenomena and in case of metal components additionally a variety of tribochemical reaction products and layers. Otherwise preliminary wear particle characterisations of ceramic debris from the simulator lubricant raise the expectation of a reduction of wear induced limitations of the functional life of total hip replacements. As to the wear performance of 57 collected ceramic retrieval couples the means for a pre-clinical validation seem unsatisfactory. The methods measuring wear directly still seem not to be able to enter a standard on the wear evaluation of hard on hard combinations made of currently available materials.

A bioactive glass, previously described in literature, was clinically tested as a coating for hip prostheses. The glass was designed to be degradable in-vivo. Early implants in humans have been performed in 1991, giving 8 years as the longest follow-up. Authors investigated the clinical performance of the cementless bioactive-glass coated stem versus a cemented un-coated one; they matched two groups who had equal: a)-stem design; b)-surgical technique; c)-sex distribution. Fifty-two implants of a bioactive-glass coated hip stems were studied. They showed a good clinical response and a decrease in early-6-months thigh pain. Only two loosening have been recorded up to now. No significative differences have been observed between cementless coated stems and cemented un-coated stems; this fact stresses the point that surgical technique and stem design are probably more important than materials alone for the good outcome of hip prostheses.

A new design concept for artificial knee joint was proposed based on fatigue properties of UHMWPE. Delamination is caused by fatigue of the polyethylene accelerated by some physical and chemical factors. In this study, the delamination was reproduced using sliding fatigue testing machine and an influence of loading condition on the crack formation was examined. The subsurface cracks were observed by scanning acoustic tornography(SAT). The results showed that the fatigue process was accelerated by complicated sliding motion. It was suggested that simplified articulating movement would be one possible solutions to prevent the flaking-like destruction of UHMWPE knee components. A new knee prosthesis was designed based on this concept.

Design and manufacturing criteria for any medical device should stem from a Systematic Design Management system. This approach takes you through the product design review using multifunctional teams and concurrent engineering. Products designed through this process have a higher chance of success due to all the factors being considered during an interdisciplinary approach to product development. The specifications are generally higher and this enhances product performance, product reliability and speed to market. To demonstrate this approach, a case study on the design and development of a ceramic-ceramic bearing highlights the benefits that can be achieved.