Reinforced Hydroxyapatite Coatings Research Articles

In Vitro Wear of Titanium Reinforced Hydroxyapatite Coatings in Simulated Body Fluid

Abstract Titanium-reinforced hydroxyapatite (Ti-HAP) coatings have been deposited over 254 SMO stainless steel using a low-velocity oxygen fuel technique. FESEM, XRD, Vickers microhardness, and shear strength tests have been performed to characterize the developed coatings. Further, in vitro wear behaviors of the coatings were evaluated using a pin-on-disc wear tester in simulated body fluid. The results reveal that 40Ti-HAP coating possesses superior wear resistance compared to 60Ti-HAP, Ti, and HAP coatings, attributed to higher surface hardness and higher shear strength values. Amongst the tested samples, the friction coefficient was lower for Ti coating, followed by 60Ti-HAP composite coating. The surface roughness was a prominent factor in reducing the friction coefficient of coating samples. Local detachment and brittle fracture were the dominant wear modes in Ti-HAP coating, whereas an additional micro-plowing wear mode was observed in pure hydroxyapatite and titanium coating.

Enhancing the performance of reinforced hydroxyapatite coatings through post coating treatment

To enhance the metallurgical, mechanical, and biological properties of medical implants in bodily fluid environments, biocompatible coatings are applied to biomaterials. These biocompatible coatings have a porous structure that promotes effective osseointegration and the ability to prevent harmful ions from metal from seeping into the surrounding bodily environment. In the present study, the impact of the addition of Tantlum carbide (TaC) with 5 and 10 wt% as reinforcement in hydroxyapatite (HA) on the morphology, mechanical and cell viability of plasma-sprayed coatings were investigated. The post-coating treatments are carried on pure HA, HA-R5(HA+5%TaC) & HA-R10 (HA+10%TaC) coatings at 900 °C and at low-temperature treatment at −196 °C. The results showed that heat treatment affects the crystallinity, surface roughness, and bond strength under different high-temperature and low-temperature treatments. Further, in-vitro results show that post-treated samples have more survival of cells as compared to as-sprayed samples. Also, heat-treated and reinforced HA coatings showed no toxicity.

In vitro assessment of plasma-sprayed reinforced hydroxyapatite coatings deposited on Ti6Al4V alloy for bio-implant applications

In vitro assessment of plasma-sprayed reinforced hydroxyapatite coatings deposited on Ti6Al4V alloy for bio-implant applications

Impact of post-heat-treatment on the surface-roughness, residual stresses, and micromorphology characteristics of plasma-sprayed pure hydroxyapatite and 7%-Aloxite reinforced hydroxyapatite coatings deposited on titanium alloy-based biomedical implants

The biocompatible hydroxylapatite (Ca10(PO4)6(OH)2) (HA) coating is usually depositing on the titanium substrate to enhance the healing process of implant and to isolate it from the harsh body environment. However, poor mechanical properties of HA restrict its usage for orthopedic applications like hip and knee joints which have to bear the load. The biocompatibility is provided by HA and mechanical strength by the addition of reinforce with HA. Thermal post treatments have been mostly utilized to enhance the morphological and physicomechanical characteristics of as-deposition coatings. In the present research, the emphasis has been laid to analyze the outcome of thermal-processing on phases of hydroxyapatite in coatings developed by plasma spraying process. The surface-morphology of as-sprayed and thermally-processed, HA coated samples was studied using Scanning electron microscope (S.E.M.), Elemental-mapping, X-ray diffraction analysis (X.R.D.), and Fourier-transform infrared (F.T.-I.R.) spectroscopy techniques. The outcomes achieved from the X.R.D. analysis of the hydroxylapatite-coated samples after thermal-treatment reveal the formation of crystalline structure at 750 °C with some traces of CaO. Moreover, when the heat treatment was further done at 950 °C, the unwanted CaO was totally eliminated and coating with crystalline structure was obtained. No substrate element is visible in the X-ray mapping of coatings. The presence of ultrafine particles was observed on both substrates after the heat treatment of coatings at specified temperatures for 2hr in air. These ultrafine particles have the capability to bond with the bone and also helps for bone in-growth on their surfaces.

Wear studies on plasma-sprayed pure and reinforced hydroxyapatite coatings

The wear properties of hydroxyapatite (HApure) coatings and HApure coatings reinforced with 15 wt-%aluminiumoxide(Al2O3) are described in this paper. Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray Spectroscopy (EDX) and X-ray Diffraction (XRD) were used to examine the coated samples. Wear tests on coatings were carried out using a Tribometer (Ball on a disc assembly). The wear resistance in HA+15 wt-% Al2O3 coatings (wear rate = 4.9 × 10−3 mm3/N-m) was found to be better than HApure coatings (wear rate = 8.4 × 10−3 mm3/N- m).The results revealed that adding Al2O3 to the coatings has a considerable impact on their tribological properties.

CHARACTERIZATION AND ELECTROCHEMICAL CORROSION ANALYSIS OF HEAT-TREATED REINFORCED HA COATINGS DEPOSITED BY VACUUM PLASMA SPRAY TECHNIQUE

Herein, a biomimetic coating of hydroxyapatite (HA)–Al2O3 and HA–ZrO2 was deposited on Ti–6Al–4V-alloy using vacuum plasma spray (VPS) technique. The bond-coat of ZrO2 has been introduced between the substrate and reinforced HA coatings to study the effect of bond-coat on structural, mechanical properties and electrochemical corrosion performance of the developed coatings. In addition, the impact of thermal treatment of coating was investigated on these properties too. Coating characteristics, such as morphology, porosity, surface roughness, and crystallinity were investigated. The corrosion performance of coatings was tested in Hank’s-based salt solution (HBSS). Significant enhancement in crystallinity and surface-hardness has been witnessed after heat treatment; nevertheless, porosity reduced. The electrochemical corrosion study revealed that the corrosion resistance of heat-treated samples was better than the as-sprayed coatings samples. The intensity of XRD peaks of all coatings increased after 24[Formula: see text]h immersion in HBSS for the electrochemical test in comparison to the intensity of peaks before the corrosion test.

Soapstone reinforced hydroxyapatite coatings for biomedical applications

Mechanical resistant bioactive materials are of high interest for biomedical applications. In this work, we address the improvement in mechanical properties of HA coatings by the addition of a cheap and widely available secondary phase material, the talc from soapstone. The composites hydroxyapatite/talc (HA/talc) were successfully obtained by pulsed electrodeposition and characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, Raman spectroscopy, corrosion and wear resistance and biocompatibility tests. We found that the addition of talc greatly improves the mechanical properties of coatings (i. e., wear track and friction coefficient in wear tests were significantly diminished) without diminishing corrosion resistance and biocompatibility. Alamar Blue® tests, alkaline phosphatase activity, and collagen production indicate that the biocomposites are biocompatible and talc itself induce bone maturation.

In-vitro performance of reinforced hydroxyapatite coatings deposited using vacuum plasma spray technique on Ti-6Al-4V

In this investigation the basic in-vitro assessment of substrate (Ti-6Al-4V), as-deposited and heat treated reinforced HA coatings has been performed to evaluate the biocompatible conduct of these bio-ceramic coatings. Briefly adherent fibroblast cell lines NIN3T3 and non-adherent human peripheral blood monocyte cells (hPBMCs) were utilized to survey the surface biocompatibility utilizing standard MTT, trypan blue tests while their reactive oxygen species profiling was done to comprehend the potential pressure that may hamper the human cell working. The outcomes demonstrated that the as-deposited and heat treated coatings displayed incredible cell reasonability for hPBMCs and NIN3T3 cells in contrast with bare substrates. Comparative results were observed for trypan blue dye exclusion assay. Besides, oxygen free radical levels demonstrated that there is no change in reactive oxygen species (ROS) levels in cells cultured on heat treated coatings. This suggests the materials utilized in coatings are not cytotoxic in nature and the phenomenon was true both for cell lines just as human primary cells. By and large natural assessment showed that coatings are protected to human cells in essential conditions.

Bioactive and Tribological Behaviour of Atmospheric Plasma Sprayed Hydroxyapatite Coatings Reinforced by Lanthanum Oxide

Lanthanum oxide (La2O3) reinforced Hydroxyapatite coating was deposited by using unique gas tunnel type plasma spray torch under optimum spraying conditions. The phase and microstructure of the as-prepared powder and coatings were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). In vitro bioactivity of the plasma sprayed lanthanum oxide reinforced hydroxyapatite coatings were investigated by using simulated body fluid solution. Results showed that there was onset of apatite formation on the surface of coatings after 15 days of immersion in SBF, while after 19 days of immersion in SBF it was indicated that a HCAp phase crystallized on their surface. Our studies demonstrate that lanthanum oxide reinforced hydroxyapatite coatings are potentially useful biomaterials with good tribological and bioactive behaviour.

Mechanical behavior of plasma-sprayed pure and reinforced hydroxyapatite coatings on Ti6Al4V alloy

Hydroxyapatite coatings with secondary reinforcement have attracted the attention of the researchers of concerned field. Reinforcement like alumina and titania are used to make the HA coatings more wear resistant. It has been reported in the existing published literature that wear and corrosion are the main cause of the bio-implant failure. This paper deals with the abrasive wear and electrochemical corrosion behavior of as-sprayed and heat-treated pure and 10 wt% 80Al2O3-TiO2-reinforced hydroxyapatite coatings successfully deposited by atmospheric plasma spray technique. Simulated body fluid (SBF) was prepared in laboratory to be used in electrochemical corrosion testing. Samples were dipped in SBF before abrasive wear testing. The coatings were characterized by XRD and SEM-EDAX analysis. Post-coating heat treatment was carried out at 700 and 800 °C. It has been found that post-coating heat treatment at 700 °C has favorable impact on both corrosion and wear resistance of coatings along with hardness and crystallinity of the coatings.

Influence of post coating heat treatment on microstructural, mechanical and electrochemical corrosion behaviour of vacuum plasma sprayed reinforced hydroxyapatite coatings.

In the present study, reinforced hydroxyapatite (HA) coatings (HA + 10 wt% Al2O3 and HA + 10 wt% ZrO2) were deposited on SS-316 L substrate with an intermediate layer (bond coat) of zirconia by vacuum plasma spray technique. The so-formed reinforced HA coatings were heat treated at 700 °C for 1 h. The influence of post coating heat treatment on phase composition, microstructure, mechanical and electrochemical corrosion properties were investigated. As-sprayed and heat treated coatings were characterized by x-ray diffraction, scanning electron microscope, surface roughness, porosity and crystallinity. Results showed that after post coating heat treatment, the structural integrity of HA has been completely re-established. Moreover, significant drop in porosity has been observed due to the sintering effect produced by heat treatment. Considerable improvement in nanohardness and shear strength was witnessed; however, the nanohardness of top layer was decreased after annealing due to the weak bonding of partially melted and un-melted particles with fully melted splats caused by diffusion process. As-sprayed coatings exhibited higher wear resistance compared to heat treated coatings. Nevertheless, post coating heat treatment effectively enhanced the corrosion resistance of coatings, since, the heat treatment lead to densification of coatings microstructure which further reduces the active sites for dissolution.

Characterization and mechanical behaviour of reinforced hydroxyapatite coatings deposited by vacuum plasma spray on SS-316L alloy.

Hydroxyapatite powder reinforced individually with 10wt percentage (wt%) of Al2O3 and ZrO2 (HA + 10wt% Al2O3 and HA + 10wt% ZrO2) was thermally sprayed onto SS-316L substrate with a bond coat of Zirconia by vacuum plasma spray (VPS) technique. The resulted coatings were heat treated at 700°C for 1h to study its effects on microstructural and mechanical properties of the deposited coatings. The characterization of the coatings was carried out using scanning electron microscope, x-ray diffraction, porosity, surface roughness and crystallinity using Rietveld analysis. The results indicated that after post coating heat treatment substantial decrease in porosity was witnessed along with significant improvement in crystallinity. Besides, the hardness across the cross-section of the coatings and bond strength was considerably improved; however the hardness of top coat was reduced owing to the loosening of un-melted and partially melted particles by diffusion process which takes place during heat treatment.

Mechanical properties of nanodiamond-reinforced hydroxyapatite composite coatings deposited by suspension plasma spraying

Hydroxyapatite (HA) coatings suffer from poor mechanical properties, which can be enhanced via incorporation of secondary bioinert reinforcement material. Nanodiamond (ND) possesses excellent mechanical properties to play the role as reinforcement for improving the mechanical properties of brittle HA bioceramic coatings. The major persistent challenge yet is the development of proper deposition techniques for fabricating the ND reinforced HA coatings. In this study, we present a novel deposition approach by plasma spraying the mixtures of ND suspension and micron-sized HA powder feedstock. The effect of ND reinforcement on the microstructure and the mechanical properties of the coatings such as hardness, adhesive strength and friction coefficient were examined. The results showed that the ND-reinforced HA coatings display lower porosity, fewer unmelted particles and uniform microstructure, in turn leading to significantly enhanced mechanical properties. The study presented a promising approach to fabricate ND-reinforced HA composite coatings on metal-based medical implants for potential clinical application.

Mechanical properties of vacuum plasma sprayed reinforced hydroxyapatite coatings on Ti-6Al-4V alloy

The aim of this present work was to deposit reinforced hydroxyapatite coatings with a bond coat of zirconia on Ti-6Al-4V substrate using the vacuum plasma spray technique in order to improve the surface properties. To achieve that, HA + 10 wt% Al2O3 and HA + 10 wt% ZrO2 coatings with an intermediate layer of zirconia were deposited on Ti-6Al-4V implant substrate. Further, these coatings were subjected to post-coating heat treatment at 700 °C for 1 h. The morphology and phase analysis of bio-ceramic powders, as-sprayed and heat-treated coatings, have been characterized using a scanning electron microscope and an X-ray diffractrometer. Crystallinity, surface roughness, porosity, hardness and shear strength were also investigated. The wear behaviour of the coatings was evaluated using a Taber abrasion tester as per ASTM F1978 standard. The results indicate that heat-treated coatings exhibit lower wear resistance than as-sprayed coatings and show lower porosity and higher crystallinity and hardness after heat treatment. Slight improvement in shear strength was observed after heat treatment.

Characterization of Vacuum Plasma Sprayed Reinforced Hydroxyapatite Coatings on Ti–6Al–4V alloy

Two reinforced hydroxyapatite (HA) coatings with an intermediate layer of zirconia were deposited on Ti–6Al–4V by vacuum plasma spray (VPS) technique. In first coating, HA was reinforced with 10 wt % Al2O3 whereas in second coating, HA was reinforced with 10 wt % ZrO2. The objective of this study was to investigate the microstructure, phase formation and mechanical properties like hardness and bond strength of as-sprayed coatings and the coatings after post coating heat treatment at 700 °C for 1 h. The characterization of the coatings was performed by using SEM/EDAX, XRD, porosity, crystallinity and roughness measurement. The coatings were also evaluated for mechanical properties like hardness and tensile bond strength. It was observed that after post coating heat treatment, crystallinity increased and porosity decreased which indicated recrystallization of amorphous phases of as-sprayed coatings. Heat treatment resulted into improvement in cross-sectional hardness, however sharp decrease in bond strength was observed.

Hydroxyapatite and YSZ Reinforced Hydroxyapatite Coatings by Gas Tunnel Type Plasma Spraying

Chemical structure of hydroxyapatite (HA) is very close to human bone which makes it compatible with the tissue of the human body. Its good biocompatibility makes it to be used extensively in many prosthetic applications, especially as a porous material for optimal bone in growth. Currently, this material is being deposited on bio-inert metallic implants and used as recovery parts in human body. In this present study a high-power plasma jet known as gas tunnel type plasma torch (GTTP), was used to produce HA and YSZ reinforced HA coatings on stainless steel substrate. In this study, microstructure, tribological properties and bioactivity of the GTTP sprayed HA and YSZ reinforced HA coatings was investigated. The XRD spectra of the as-sprayed coatings showed that the as-sprayed pure HA coating retained its crystalline HA phase similar to the initial feed stock HA powder, even though there existed a possibility for occurrence of decomposition during its in-flight in high temperature plasma zone. In the present case the decomposition processes of in-flight HA could be well controlled by means of selective operating parameters and unique nature of GTTP jet. The presence of un-melted particles and pores inside the coating microstructure play a vital role in the bonding strength of the coating.

Mechanical properties, electrochemical corrosion and in-vitro bioactivity of yttria stabilized zirconia reinforced hydroxyapatite coatings prepared by gas tunnel type plasma spraying

Yttria stabilized zirconia reinforced hydroxyapatite coatings were deposited by a gas tunnel type plasma spray torch under optimum spraying conditions. For this purpose, 10, 20 and 30 wt% of yttria stabilized zirconia (YSZ) powders were premixed individually with hydroxyapatite (HA) powder and were used as the feedstocks for the coatings. The effect of YSZ reinforcement on the phase formation and mechanical properties of the coatings such as hardness, adhesive strength and sliding wear rates was examined. The results showed that the reinforcement of YSZ in HA could significantly enhance the hardness and adhesive strength of the coatings. The potentiodynamic polarization and impedance measurements showed that the reinforced coatings exhibited superior corrosion resistance compared to the HA coating in SBF solution. Further the results of the bioactivity test conducted by immersion of coatings in SBF showed that after 10 days of immersion of the obtained coatings with all the above compositions commonly exhibited the onset of bioactive apatite formation except for HA+10%YSZ coating. The cytocompatibility was investigated by culturing the green fluorescent protein (GFP)-labeled marrow stromal cells (MSCs) on the coating surface. The cell culture results revealed that the reinforced coatings have superior cell growth than the pure HA coatings.

Role of Post Heat Treatment of Plasma Sprayed Pure and Al<sub>2</sub>O<sub>3</sub>-TiO<sub>2</sub> Reinforced Hydroxyapatite Coating on the Microstructure and Mechanical Properties

Pure and 10 wt% 80Al2O3-20TiO2 reinforced hydroxyapatite coatings were successfully deposited on Ti6Al4V substrate by plasma spray technique for bio medical applications. Post coating heat treatment was carried out to study the effect of heat treatment on improvement in micro structure and mechanical properties of coatings. Coating was characterized by SEM/EDAX and XRD analysis. Positive impact of post coating heat treatment was observed in microstructure, surface roughness and micro hardness of both coatings.

Plasma-sprayed carbon nanotube reinforced hydroxyapatite coatings and their interaction with human osteoblasts in vitro

Carbon nanotubes (CNT) possess excellent mechanical properties to play the role as reinforcement for imparting strength and toughness to brittle hydroxyapatite (HA) bioceramic coating. However, lack of processing technique to uniformly distribute multiwalled CNTs in HA coating and limited studies and sparse knowledge evincing toxicity of CNTs has kept researchers in dispute for long. In the current work, we have addressed these issues by (i) successfully distributing multiwalled CNT reinforcement in HA coating using plasma spraying to improve the fracture toughness (by 56%) and enhance crystallinity (by 27%), and (ii) culturing human osteoblast hFOB 1.19 cells onto CNT reinforced HA coating to elicit its biocompatibility with living cells. Unrestricted growth of human osteoblast hFOB 1.19 cells has been observed near CNT regions claiming assistance by CNT surfaces to promote cell growth and proliferation.

Titanium dioxide reinforced hydroxyapatite coatings deposited by high velocity oxy-fuel (HVOF) spray

Hydroxyapatite (HA) coatings with titania addition were produced by the high velocity oxy-fuel (HVOF) spray process. Mechanical properties of the as-sprayed coatings in terms of adhesive strength, shear strength and fracture toughness were investigated to reveal the effect of the titania reinforcement on HA. Qualitative phase analysis with X-ray diffraction (XRD) showed that mutual chemical reaction between TiO 2 and HA, that formed CaTiO 3 occurred during coating formation. Differential scanning calorimetry (DSC) analysis of the starting powders showed that the mutual chemical reaction temperature was ∼1410°C and the existence of TiO 2 can effectively inhibit the decomposition of HA at elevated temperatures. The positive influence of TiO 2 addition on the shear strength was revealed. The incorporation of 10 vol% TiO 2 significantly improved the Young's modulus of HA coatings from 24.82 (±2.44) GPa to 43.23 (±3.20) GPa. It decreased to 38.51 (±3.65) GPa as the amount of TiO 2 increased to 20 vol%. However, the addition of TiO 2 has a negative bias on the adhesive strength of HA coatings especially when the content of TiO 2 reached 20 vol%. This is attributed to the weak chemical bonding and brittle phases existing at the splats’ interface that resulted from mutual chemical reactions. The fracture toughness exhibited values of 0.48 (±0.08) MPa m 0.5, 0.60 (±0.07) MPa m 0.5 and 0.67 (±0.06) MPa m 0.5 for the HA coating, 10 vol% TiO 2 blended HA coating and 20 vol% TiO 2 blended HA coating respectively. The addition of TiO 2 in HA coating with the amount of less than 20 vol% is suggested for satisfactory toughening effect in HVOF HA coating.