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Magnesium is light, biocompatible and has similar mechanical properties to natural bone, so it has the potential to be used as a biodegradable material for orthopedic applications. However, pure magnesium severely corrodes in a physiological environment, which may hinder its use for in vivo applications. Protective coatings are effective method to delay the corrosion of Mg. In this study, sol-gel and hydroxyapatite (HA) coatings were applied onto the surface of pure magnesium substrates using a biomimetic technique. The corrosion rate of surface-treated substrates was tested. It was found that both types of coatings substantially slowed down the corrosion of the substrate, the 60Ca so-gel and HA coating was more effectively than the 100Si so-gel and HA coating in hindering the degradation of the substrate. Thus, the corrosion rate of magnesium implants can be closely tailored by coating sol-gel then coating apatite thereby monitoring the release of magnesium ions into the body.
Two types of hydroxyapatite (HA) coatings onto carbon/carbon composite (C/C composites) substrates, deposited by plasma spraying technique, were immersed in a simulated body fluid (SBF) in order to determine their behavior in conditions similar to the human blood plasma. Calcium ion concentration, pH value, microstructure, and phase compositions were analyzed. Results demonstrated that both the crystal Ca–P phases or the amorphous HA do dissolve slightly, and the dissolution of CaO phases in SBF was evident after 1 day of soaking. The calcium-ion concentration was decreased and the pH value of SBF was increased with the increasing of the immersing time. The precipitation was mainly composed of HA, which was verified by X-ray diffraction (XRD) and electron-probe microanalyzer.
Glass-ceramics containing only apatite and wollastonite crystals were produced in the system MgO-CaO-SiO2-P2O5-F by the melt casting process. The bioactivity of the glass-ceramics was determined by immersing the glass-ceramics in a simulated body fluid (SBF) and by assessing the resulting apatite formation on the free surface after various immersion durations. A 12-μm-thick apatite layer formed on the surface of the glass-ceramic containing only apatite crystals after 20 days immersion in SBF. However, the thickness of the apatite layer formed on the surface of the glass-ceramic containing apatite and wollastonite crystals was 1 μm. Results have shown that the bioactivity of glass-ceramic depends strongly on the type of crystal(s) developed during the glass-ceramic process and their proportion in the glassy matrix.
The friction and wear behavior of the as-cast Mg–6Gd–2Zn–0.4Zr (wt.%, GZ62K) alloy has been studied under dry and simulated body fluid (SBF) conditions for orthopedic application. The results show that the friction coefficient in SBF is much lower than that under dry sliding condition. The mass loss in SBF is lower than that of dry sliding condition before the corrosion products were removed but higher after they were removed. In SBF, wear is significantly alleviated due to lubrication and corroded film, but corrosion is extremely aggravated by wear debris. It is indicated that corrosion contributes much more mass loss than wear with the increase of sliding time.
Magnesium composites stay relevant for the applications of biodegradable implant as they are harmless and possess characteristics such as density and elastic modulus analogous to the cortical bone in humans. But corrosion is one major issue associated with magnesium when the biomedical applications are contemplated. Moreover, load bearing abilities are also required in case of an orthopedic implant. In this study, to achieve the desired implant characteristics, hybrid nanocomposites (HNCs) of Mg–2.5Zn binary alloys such as metal matrix, hydroxyapatite (HAp), and reduced graphene oxide (rGO) as reinforcements were fabricated via the vacuum-assisted stir casting method. The overall weight percentage of the reinforcements was fixed at 3% and both the reinforcements varied in compositions by weight to prepare the samples S0 (Pure Magnesium), S1 (Mg–2.5Zn–0.5HAp–2.5rGO), S2 (Mg–2.5Zn–1.0HAp–2.0rGO), S3 (Mg–2.5Zn–1.5HAp–1.5rGO), S4 (Mg–2.5Zn–2.0HAp–1.0rGO), and S5 (Mg–2.5Zn–2.5HAp–0.5rGO), respectively. The influence of mechanical characteristics such as tensile strength, compressive strength, and microhardness as well as the corrosion over the surface of the nanocomposite in simulated body fluid (SBF) have been assessed for their suitability as biodegradable orthopedic implants. Results suggest that the fabricated nanocomposites exhibit superior characteristics in comparison to pure magnesium. Increasing the HAp from 0.5 wt.% to 2.5 wt.% enhanced the compressive strength and reduced the corrosion rate. On the other hand, increasing the rGO from 0.5 wt.% to 1.5 wt.% increased the tensile strength. The formation of apatite layer over the composites is observed in the SBF solution. Among all the fabricated hybrid nanocomposite samples, the sample S3 (Mg–2.5Zn–1.5HAp–1.5rGO) with equal wt.% of HAp and rGO exhibited 209.60 MPa of ultimate tensile strength, 300.1 MPa of ultimate compressive strength, and a corrosion rate of 0.91 mm/year thus making it the best suited and a prospective material for biodegradable implant application.
Graphene based nanomaterials have attracted tremendous attention for their potential applications in various fields. In the present investigation, the growth of graphene on silicon substrate using thermal chemical vapor deposition (Thermal-CVD) method has been reported and the biocompatibility of obtained yield has been critically assessed. Raman spectra confirm the formation of graphene which was found to be the best to obtain minimal number of layers of graphene. Three prominent peaks have been observed at approximately 1360cm−1 (D Peak), 1595cm−1 (G Peak) and 2700cm−1 (2D Peak). Haemolysis test and simulated body fluid (SBF) test are performed to check the biocompatibility of the synthesized graphene samples. Atomic force micrographs of the samples are taken prior and after soaking them in SBF solution to study their interaction with the fluid. Haemolysis percentage is determined using UV-Vis to determine the hemocompatible nature of the samples. The results of haemolysis and SBF test demonstrated that Thermal-CVD grown graphene samples are biocompatible.
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.
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).
Magnesium composites stay relevant for the applications of biodegradable implant as they are harmless and possess characteristics such as density and elastic modulus analogous to the cortical bone in humans. But corrosion is one major issue associated with magnesium when the biomedical applications are contemplated. Moreover, load bearing abilities are also required in case of an orthopedic implant. In this study, to achieve the desired implant characteristics, hybrid nanocomposites (HNCs) of Mg–2.5Zn binary alloys such as metal matrix, hydroxyapatite (HAp), and reduced graphene oxide (rGO) as reinforcements were fabricated via the vacuum-assisted stir casting method. The overall weight percentage of the reinforcements was fixed at 3% and both the reinforcements varied in compositions by weight to prepare the samples S0 (Pure Magnesium), S1 (Mg–2.5Zn–0.5HAp–2.5rGO), S2 (Mg–2.5Zn– 1.0HAp–2.0rGO), S3 (Mg–2.5Zn–1.5HAp–1.5rGO), S4 (Mg–2.5Zn– 2.0HAp–1.0rGO), and S5 (Mg–2.5Zn–2.5HAp–0.5rGO), respectively. The influence of mechanical characteristics such as tensile strength, compressive strength, and microhardness as well as the corrosion over the surface of the nanocomposite in simulated body fluid (SBF) have been assessed for their suitability as biodegradable orthopedic implants. Results suggest that the fabricated nanocomposites exhibit superior characteristics in comparison to pure magnesium. Increasing the HAp from 0.5 wt.% to 2.5 wt.% enhanced the compressive strength and reduced the corrosion rate. On the other hand, increasing the rGO from 0.5 wt.% to 1.5 wt.% increased the tensile strength. The formation of apatite layer over the composites is observed in the SBF solution. Among all the fabricated hybrid nanocomposite samples, the sample S3 (Mg–2.5Zn–1.5HAp–1.5rGO) with equal wt.% of HAp and rGO exhibited 209.60 MPa of ultimate tensile strength, 300.1 MPa of ultimate compressive strength, and a corrosion rate of 0.91 mm/year thus making it the best suited and a prospective material for biodegradable implant application.