Surface Engineering and Performance of Biomaterials

The following sections are included:

• Preface
• Contents

Bone grinding is a craniotomy procedure which is used to remove a bone flap from the skull to expose and create an access for the dissection of tumors. In this study, a computer-controlled neurosurgical bone grinding has been used to explore the effect of various neurosurgical bone grinding parameters, such as cutting forces, torque, grinding force ratio, and temperature generated during bone grinding have been investigated. Bone samples after grinding have been assessed for morphological analysis. Based on the outcomes, a multi-attribute decision-making methodology based on grey relational analysis has been adopted. Regression models have been developed and then validated to ensure the adequacy of the developed models. Subsequently, a comparative analysis of experimental and predicted results have been presented. It is revealed that grinding forces and torque decreased with the escalation of rotational speed from 35,000 revolutions per minute (rpm) to 55,000 rpm. The optimum combination of process parameters found as rotational speed of 55,000 rpm, feed rate of 20mm/min, and depth of cut of 0.50 mm.

An upsurge in demand and extensive effort in orthopedic implants directed toward innovative biomaterials for orthopedic applications. Orthopedic implants are significantly used in mature alternatives to retain, restore or modify the defective bone or tissue. However, exhaustive research in the past reveals various health-associated problems that can be effectively overcome by inventing newer kinds of biomaterials. The selection of optimal materials and the fabrication process are crucial challenges enforced by numerous novel materials that could be made for orthopedic applications. This paper intends to systematically assess the processing method employed in manufacturing the biomaterials for orthopedic applications. However, the success of biomedical implants in orthopedic are commonly restricted owing to insufficient bone-implant integration, wear debris induced osteolysis, and implant-associated infections. Nevertheless, the endeavor has also been intended to enhance the biological properties of the biomaterials by surface modification process while retaining their strength and hardness. Furthermore, various surface modifications have been comprehended. This review conferred contemporary advancements in surface coating approaches in orthopedic to enhance their osteointegration, improve corrosion resistance and accomplish antibacterial performance, clinical success and long-term service. The insight review has revealed the current outcomes in the field of engineering biomaterials concerning surface modifications of metallic implants or composite for enhancing their biological properties.

Zirconia and zirconia toughened alumina (ZTA) are widely used for biomedical applications. Owing to the superior mechanical and biocompatible properties of ZTA, it is now gaining more importance over zirconia, as it has the profound strength of zirconia and alumina. This study examines the tribological behavior of Zirconia and ZTA balls sliding against a Ti6Al4V disc using the Ball-on-disc (BOD) Tribometer. The effect of loads and bio-lubricants influencing the tribological behavior is investigated for a sliding distance of 2 km using BoD Tribometer. The friction and wear coefficients are examined under these loading and lubrication conditions. Five bio-lubricants considered for the tribological study of biomaterials include ringer’s solution, phosphate buffer saline (PBS), distilled water, NaCl 0.9% saline solution and sesame oil. The result showed that ZTA had a lower coefficient of friction (CoF) value of 0.34 for NaCl bio-lubricant. The ZTA and zirconia exhibited the least wear coefficient values under sesame oil lubrication. Overall, ZTA had better CoF under high loads for PBS, distilled water and sesame oil bio-lubricants. However, zirconia exhibited a better wear coefficient under all loads and lubrication conditions.

In this work, the experimental investigation of the surface integrity and biomechanical properties of the superficial layer obtained by wire electrical discharge machining (W-EDM) of Ti-6Al-4V alloy for biomedical application has been carried out. The surface morphology and elemental composition of the superficial layer have been investigated by field-emission scanning electron microscope (FE–SEM) and energy dispersive X-ray spectroscopy (EDS) techniques. The micro-mechanical behavior in terms of compressive strength and surface hardness was studied using the micro-pillar and nanoindentation technique. The corrosion resistance and in vitro bioactivity have been investigated using electro-chemical and immersion test. Morphological analysis showed that surface morphology and superficial layer thickness were affected by peak current, pulse-duration and pulse-interval. The niobium (Nb)-rich layer was developed in superficial layer zone. The low peak current (3–6 A), low pulse-duration (5–10 μs) and high pulse-interval (> 45 μs) have been recommended for better surface morphology and thin superficial layer (ranging from 4–6 μm) free from surface defects. The micro-pillar and nano-indentation results showed that the superficial layer comprised of a brittle structure that improved the mechanical properties of the layer and the compressive strength was measured to be 1198 MPa. The corrosion resistance analysis revealed that the Nb-rich layer in the superficial layer improved the corrosion resistance and bioactivity. Excellent apatite growth has been found in the W-EDM-processed zone. The W-EDM can be used for the biomedical industry as a potential surface engineering technique.

Ti6Al4V alloy of titanium is a significant biomaterial due to its biocompatible nature, but it lacks required bioactivity to make it mimic properties to a human bone. Thus, hydroxyl-apatite (HAp), an inorganic compound found in human bones, is generally coated onto Ti6Al4V substrates to improve their bio-characteristics. But, HAp itself lacks certain bio-functionalities, such as allowing tissue bone regeneration and poor binding to the Ti6Al4V substrate, which results in osteoporosis and reduced bioactivity of the bio-implant, respectively. The proposed way out for this is the further doping of HAp with Strontium (Sr) for enabling tissue bone regeneration as well as addition of Polydopamine (PDA) for improved adhesion of HAp-based coatings with the substrate. Moreover, PDA results in increased drug delivery area and thus can be used as a material for enhancing resistance to bacterial growth. The present study demonstrates an experimental work on deposition of HAp, HAp with PDA and HAp with PDA and Sr coatings deposited onto Ti6Al4V alloy by means of biomimetic coating technique. Initially the pure HAp coatings were deposited using 10 SBF (simulated body fluid) solution and optimized in terms of time duration for desired coating uniformity. Then, for the optimized coating duration, the PDA pretreated Ti6Al4V substrates were coated, utilizing HAp, and Sr (at two different compositions) combinations were deposited through modified 10 SBF solutions. The characterization involving microstructural analysis and phase detection was performed for all these coatings using Scanned Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and X-Ray Diffraction (XRD) of the coated substrates and adhesion strength was calculated using a standard pull out adhesion test ISO 10779–4. The study showed an effective and comparatively cheap method of depositing organic coatings using biomimetic technique to obtain improved bio-functionalities in metallic implants at low temperatures.

Metallic bioimplant are widely used now-a-days to replace a part of human body in a physiologically accepted manner. However, the bio-compatibility of the metallic bioimplant was mainly achieved by the incorporation of a bio-compatible coating on its surface through suitable surface modifications techniques. In surface modifications techniques, the thermal spraying is widely used for modification of metallic bioimplant due to its versatile nature. In thermal spraying, the hydroxyapatite (HAp)-based coatings are mainly preferred because this coating responses to physiochemical environment and adapts itself accordingly. But bulk of the HAp coating give out due to less adhesion strength of the HAp coating and its poor mechanical properties. The properties of HAp-based coatings can be designed as per requirements by reinforcing this coating through hard particulates in suitable proportions. In this paper, the various thermal sprayed (TS) coatings used for performing HAp-based coatings on bioimplant were discussed. The influence of reinforcements on the mechanical and bio-compatible properties of the coatings is also discussed in detail. Lastly, the challenges in the TS HAp coatings along-with the future perspective of TS coating in fabricating of 3D biomedical implants by using cold spray (CS) has also been summarized.

Straw combines are intended to process the remaining harvested straw. When cut at high temperatures and in abrasive conditions, the cutting blade of straw combines undergoes substantial surface deterioration. This deterioration shortens the blade’s lifespan and increases the cutting cost of the machine. In recent decades, cryogenic treatments have played a significant role in enhancing material properties. In this paper, cryogenic treatment is utilized to boost the wear resistance of straw combine blades in the current investigation. The performance of cryogenic treatment was tested in the laboratory using the pin-on-disc wear tester with sample type, load, sliding velocity, and time serving as process factors and wear loss as the response parameter. The smoothness of the cryogenically-treated sample’s surface is certified through morphological examination. Specific wear rate and field emission scanning electron microscope (FE-SEM) indicated that cryogenic treatment enhances the grain structure and intermolecular interaction of the specimen, resulting in an increase in wear resistance. As opposed to the untreated specimen, the wear on the treated surface is uniform over the entire surface, as demonstrated by FE-SEM analysis. The grain structure and intermo-iecuiar bonding of the specimen were improved as a result of the cryogenic treatment. The cryogenic treatment increased the cost of the cutter bar and chopping cylinder blades by 9.38% and 13.61%, respectively, compared to untreated blades, but the increased cost was fuiiy offset by the longer blade life.

The present work deals with the fabrication of forsterite–hydroxyapatite (FS–HA) hybrid coatings on stainless-steel 316L using the pulsed laser deposition (PLD) technique. The stainless steel (SS 316L) as a metallic implant is widely used in hard tissue applications. The XRD studies have confirmed the crystalline behavior of synthesized FS powder with an average crystallite size of 54 nm. The synthesized FS powder was mixed in different compositions (10, 20, 30 wt.%) into HA for preparing PLD targets (pellets). The XRD of the prepared pellets by UTM has confirmed both phases of FS and HA. The Scanning Electron Microscopy (SEM) of the coated samples depicted the successful deposition of composite powders on the substrates (SS 316 L). The Ellipsometer was used to investigate the thickness of different substrates and it was found as 243, 251, 255, and 257 nm for CP1, CP2, CP3, and CP4, respectively. The bioactivity of the coated substrates with different compositions (pure HA, 10%, 20%, 30%, and pure FS) was investigated by immersing the samples in simulated body fluid (SBF) for 14 days. The same samples were then characterized by SEM which confirms the apatite layer formation that reflects the bioactivity. The addition of FS powder into HA will stimulate the apatite formation which enhances the bioactivity. The Raman Spectroscopy of coated samples reveals the successful deposition of different compositions of FS–HA nanocomposite. The peaks of Raman spectroscopy were corresponding to the XRD results of the pellets (different compositions of FS–HA). The antimicrobial activity of different compositions of FS–HA against Escherichia coli (E. coli) bacteria also showed a significant zone of inhibition. The bioactivity and antimicrobial behavior of FS–HA along with successful deposition by PLD have shown better potential applications for biomedical implant coating.

As implant materials, titanium and its alloys have been extensively utilized because of their exceptional mechanical properties and biocompatibility. Despite this, corporations and researchers alike have kept up their aggressive pursuit of better alloys since there are still issues that require immediate attention. One of these causes a problem with stress shielding as a noticeable variation in the elastic modulus of the implant material. Ti alloys release harmful ions after extended usage. The poor bioactivity of the Ti alloy surface slows the healing process. In order to address these problems, additional research has concentrated on developing Ti alloys for the 21st century that contain a more suitable phase and change the surface of the alloy from inherently bioinert to bioactive. This study assesses the knowledge presently existing on the biological, chemical, mechanical, and electrochemical characteristics of important β-Ti alloys created in recent years with the objective to provide scientific justification for using β-titanium-based alloys as a substitute for cpTi. Dental implants might be made using β-Ti alloys as an alternative. The enhanced alloy qualities, which include a lower modulus of elasticity, improved strength, suitable biocompatibility, and good abrasion and excellent resistance to corrosion, offer the essential proof. Additionally, structural, chemical, and thermomechanical modifications to β-Ti alloys allow for the production of materials that may be tailored to the needs of unique instances for clinical practises. By researching the paper, the performance and attributes of β-titanium alloy are compared to those of other forms of titanium alloy, such as α titanium alloys. To support their usage as cpTi substitutes, in vivo studies are required to assess new β-titanium alloys.

In this study, analyses were carried out to investigate the structural, mechanical and electrochemical behaviors of untreated and bioglass (BG)-coated Ti45Nb materials. The samples were coated with a mixture of 63s BG powder and phosphate ester (PE) at concentrations of 0.2, 0.4, 0.8, and 1 g using the electrophoretic deposition (EPD) method. Then, the structural, mechanical, and electrochemical properties of the untreated and coated samples were determined and characterized by using X-ray diffraction (XRD) and scanning electron microscope (SEM) devices. It was concluded that the 0.2 g coating provided resistance to corrosion for the Ti45Nb material more effectively than the others did.

The aim of this in-vitro study was to evaluate the influence of Ag⁺-ion-coated conditions on the corrosion, tribocorrosion and antibacterial properties of Ti15Mo alloy. The mean wear volume losses of all test specimens after tribocorrosion test procedures were determined using a noncontact 3D profilometer. The specimens’ hardness, roughness values and microstructures were measured using the microhardness tester, surface profilometer, scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. The mean wear volume loss of 30-min Ag⁺-ion-coated Ti15Mo alloy was lower than the other specimens. In this study, correlations between the hardness, surface roughness and wear volume loss were found to be significant. The PVD coating process enhanced the anti-bacterial activity of Ti15Mo alloy owing mainly to the formation of silver film on the substrates.

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.