Sprayed Hydroxyapatite Coatings Research Articles

Most commonly used metallic biomaterials for plasma sprayed hydroxyapatite coatings

In load bearing implants metallic biomaterials have the first preference in orthopedic surgery because of their good mechanical properties which satisfied the prerequisite of human cortical bone. However metallic implants have limitations of poor wear resistance and release of metal ions resulting in to implant failure. To overcome these limitations hydroxyapatite based coatings on metal substrate can be used. The application of hydroxyapatite coating with the second reinforcement improve the fatigue strength of composite coatings. In this paper, commonly used metallic biomaterials for application of hydroxyapatite based composite coatings are discussed. Plasma spray coating technique with variable process parameters has been considered for this review. Presently plasma spray technique is commonly used for application of HA coatings in medical industry.

Efficacy of Graphene Nanosheets on the Plasma Sprayed Hydroxyapatite Coating: Improved Strength, Toughness and In-Vitro Bioperformance With Osteoblast

Graphene nanosheet (GNS) reinforced HA coating on Ti6Al4V substrate, fabricated using plasma spray, was developed for biomedical applications. Microstructural observation corroborated that the adding GNSs homogeneously distributed in the GNS/HA coating with typical lamellar structure featured by GNSs acting as binder between the discrete HA splats. Meanwhile, GNSs were observed to get in direct contact with HA matrix and form a clean GNS-HA interface without interfacial product. Results of various indentation tests showed simultaneous improvement in both indentation yield strength (~379 MPa) and fracture toughness (0.78±0.17 MPam1/2 ), mainly attributing to synergetic toughening and strengthening mechanisms associated with the adding GNSs such as load transfer, GNS pull-out, inter-layer sliding of a GNS, crack branching, GNS bridging and crack deflection. In addition, the GNS/HA coating exhibited improved biocompatible with MG-63 cell in terms of its attachment, adhesion strength, proliferation and differentiation. Hence, the GNS/HA composite coating with improved strength, toughness and enhanced biocompatibility makes it a promising candidate for bone regeneration and implantation.

Collagen Coating of Titanium Implants Using Nonthermal Plasma

Surface modification of implants is now an essential aspect of biocompatibility. A single step process to attach biomolecules to implants would represent a major advance and plasma coating could potentially achieve this. An aqueous solution of collagen was sprayed into a non-thermal plasma and deposited onto titanium surfaces. The plasma instantly transformed the liquid aerosol into a coagulated dry coating on the implant surface. Surface analysis confirmed the presence of a thin, conformal protein layer on the metal surface. A series of titanium fixation screws were coated first with hydroxyapatite and then with a layer of collagen and were implanted into the femurs of New Zealand white rabbits and compared to various control surfaces. Measurements of the rotational torque removal force indicated that the collagen coating enhanced bone fixation and created a more reproducible well anchored, stable implant than the traditional plasma sprayed hydroxyapatite coatings. Non-thermal plasma processing offers a single step route to the biological functionalisation of implantable surfaces. The process requires no polymers, primers or linkers and offers an opportunity to control biocompatibility and to tailor the local response to the implant in vivo. This opens the door to a wide variety of novel biological surface coatings across all aspects of life sciences and medicine.

Microstructure and Corrosion Characterization of a MgO/Hydroxyapatite Bilayer Coating by Plasma Electrolytic Oxidation Coupled with Flame Spraying on a Mg Alloy.

Thermally sprayed hydroxyapatite coatings are one of the main strategies to improve the bioactivation of metal implants. However, the naturally low corrosion resistance of these coatings is the main challenge for their use. In this study, plasma electrolytic oxidation (PEO) was used to create an intermediate layer. The anodization process was used for comparison. According to the polarization curves, the PEO layer was more effective than the anodized layer in reducing the corrosion current density (Icorr of 0.05 × 10–9 A/cm2 vs Icorr of 0.05 A/cm2). The results of electrochemical impedance spectroscopy showed higher resistance of the sample with a PEO interlayer than that of the sample with an anodized interlayer. The results of the hydrogen evolution test revealed that the PEO layer as a middle layer served as the main barrier for reducing the magnesium corrosion rate, especially during the initial immersion time.

Effect of Plasma Power on Corrosion Behaviour of Plasma Sprayed Hydroxyapatite Coatings

Effect of Plasma Power on Corrosion Behaviour of Plasma Sprayed Hydroxyapatite Coatings

Influence of Yttria Stabilized Zirconia and Hydrothermal Treatment on Plasma Sprayed Hydroxyapatite Coatings

A post-treatment of hydrothermal process was conducted to evaluate its effects on the material characteristics and mechanical properties of plasma-sprayed pure HA and HA/20% YSZ coatings. Surface morphology and microstructural changes, relative element contents as well as phase transformations were analyzed by scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffractometry. Both microhardness and Young’s modulus were measured. CaCO3 was found existing before and after the whole process of post-treatment. Peaks of impurity phases such as CaO, TCP, and TTCP of as-sprayed coatings were observed to disappear while HA peaks show a tendency of getting higher and wider over time. Surface morphology of SEM analysis presents a clear deposition behavior of ultrafine HA crystallized particles and cross-sectional analysis exhibits a dense and fine structure. Mechanical properties of HA/20%YSZ coatings are found to be significantly higher than those of pure HA coatings and both of which displayed an overall increase with the heating time, indicating enhanced performances.

Heat and hydrothermal treatments on the microstructure evolution and mechanical properties of plasma sprayed hydroxyapatite coatings reinforced with graphene nanoplatelets

Recent demands in clinical applications drive a large amount of research to plasma sprayed hydroxyapatite (HA) composite coatings. Herein, graphene nanosheet (GNS) reinforced HA coating was fabricated using plasma spray, the effect of heat and hydrothermal treatments (hereafter referred to as thermal treatment) on microstructural evolution and mechanical properties of the composite coating were investigated. Thermally treated GNS/HA coating not only exhibited ~47.1% improvement in HA crystallinity and more denser microstructure, but also displayed increased surface roughness (3 times of that of the as-sprayed sample) due to the fact that GNSs facilitated HA nanoparticle precipitation on the coating surface. Fracture toughness of the as-sprayed HA coating increased by up to ~44.1% at 2.0 wt% GNSs owing to GNS pullout, GNS bridging and arresting of crack propagation by the embedded GNSs. As for thermally treated HA coatings, crack propagation arrested by the sintered regions was found to act as an important toughening mechanism, but thermal treatment introduced more structural defects into the GNSs and led to the reductions in their length and thickness, resulting in negligible enhancement in toughness of the GNS/HA coating.

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.

The novel use of waste animal bone from New Zealand agricultural sources as a feedstock for forming plasma sprayed hydroxyapatite coatings on biomedical implant materials

This study presents the feasibility of using animal bone-derived hydroxyapatite (HAP) as feedstock powders for plasma spraying. Bovine, cervine and ovine bone from abattoirs was boiled in a pressure cooker to remove blood, fat and adhering meat tissue. The bone was then placed in a muffler furnace, pyrolyzed at approximately 1000 degrees C to remove collagen and resid-ual organics, cooled and subsequently ground to a powder then digested in nitric acid. Sodium hydroxide was added to the digest to reprecipitate the HAP. Ageing of the precipitate followed by filtration, extensive washing and drying produced the white powder used as the feedstock. X-ray diffractometry (XRD) and Fourier transform infrared spectroscopy (FTIR) confirmed the powder to be poorly crystalline HAP with low-level carbonate. Out of several batches of the sieved powders, one batch was plasma sprayed to produce adherent HAP coatings; therefore, demonstrating that animal bone-derived HAP powders can be seri-ously considered as a feedstock powder, subject to the powder being processed for the correct rheological characteristics for easy flowing within the plasma spray flow lines. The phase composition of the successful plasma sprayed HAP coatings on both stainless steel and titanium were found by XRD to be mainly HAP with minor contributions from á -tricalcium phosphate, tetra-calcium phosphate and CaO; therefore, demonstrating that feedstock decomposition on its passage through the plasma spray torch was insignificant under the conditions employed. Scanning electron microscopy (SEM) micrographs of the coatings indicated that their morphology featured the classical heterogeneous and splat-like appearance expected of plasma sprayed coatings. Young's modulus and Vicker's microhardness tests conducted on the coatings revealed values in the range, respectively, 22-87 GPa and 166-287 (HV200 ) indicating high strength plasma spray HAP coatings had been produced from the feedstock powder.

Effect of post-heat treatment on the microstructure of micro-plasma sprayed hydroxyapatite coatings

Hydroxyapatite (HA) is widely used as surface coatings on biomedical metal implants because of its excellent biocompatibility and osteoconductivity. In this study, HA coatings were deposited onto Ti-6Al-4V substrates by micro-plasma spraying and then heat treated at 650 °C in a muffle furnace for 3 h and 6 h. XRD results showed that, the HA peaks were sharper than those of corresponding as-sprayed coatings and the amorphous diffuse background was reduced after heat treatment. The transformation from impurity phases such as tetra-calcium phosphate (TTCP) and tri-calcium phosphate (TCP) and amorphous calcium phosphate (ACP) to crystalline HA occurred during the heat treatment. Moreover, the texture intensity was not increased during the re-crystallization of ACP and the transformation of impurity phases into HA. The SEM results showed that nanograins were formed on the coating surface. In addition, with the increase of the holding time, the nanograins become coarse.

Axial Suspension Plasma Spraying: An ultimate technique to tailor Ti6Al4V surface with HAp for orthopaedic applications.

Dissolution of atmospheric plasma sprayed (APS) hydroxyapatite (HAp) coatings on Ti-6Al-4 V medical implants have always been a challenge to overcome in the field of biomedical industry. In the present work, an attempt has been made to develop a HAp coating using a novel thermal spray process called axial suspension plasma spraying (SPS), which leads to thin adherent coatings. Two HAp coatings fabricated by APS (P1 and P2) and four SPS HAp coatings (S1, S2, S3 and S4) produced with varying spraying parameters were characterized in terms of (1) microstructure, porosity, hardness, adhesion strength, contact angle and phase purity; (2) corrosion resistance in 10% Fetal bovine serum (FBS); (3) in-vitro cell adherence and cell viability using human umbilical cord blood-derived mesenchymal stem cells (hMSCs). Amongst different APS and SPS coatings, P1 and S3 exhibited superior properties. S3 coating developed using SPS exhibited 1.3 times higher adhesion strength when compared to APS coating (P1) and 9.5 times higher corrosion resistance than P1. In addition, both S3 and P1 exhibited comparatively higher biocompatibility as evidenced by the presence of more than 92% viable hMSCs.

Wnt signalling in mesenchymal stem cells is heightened in response to plasma sprayed hydroxyapatite coatings

Wnt signalling in mesenchymal stem cells is heightened in response to plasma sprayed hydroxyapatite coatings

The Influence of Process Parameters on the Structure, Phase Composition, and Texture of Micro-Plasma Sprayed Hydroxyapatite Coatings

In this study, hydroxyapatite (HA) coatings were deposited on Ti-6Al-4V by micro-plasma spraying (MPS). The influence of the process parameters on the microstructure of HA coatings was investigated. The splat morphology and spreading behavior were examined to understand the influence of process parameters on the coating. The texture strength of HA coatings was characterized by X-ray diffraction (XRD). The texture coefficients were all applied to characterize the variation in texture. The morphology of splats and coatings were characterized by scanning electron microscopy (SEM). XRD pattern shows that the texture intensity of the c-axis of HA was greatly influenced by spraying distance and spraying current. SEM reveals the different texture strength of HA coatings with different ratios of columnar grains. The strongest c-axis texture was found in the coating by 60 mm spraying distance with a spraying current of 40 A. In the cross-section SEM images of the coating with the strongest c-axis texture, uniform distribution columnar grains were observed in the upper part (~100 μm). The investigation of splats indicates that columnar grain growth occurs after fully melted particles impact the heated substrate. By controlling the melting state prior to in-flight particle impacts, columnar grain growth can be achieved during slow solidification of the disk shape splat during MPS.

Boron nitride nanoplatelets induced synergetic strengthening and toughening effects on splats and their boundaries of plasma sprayed hydroxyapatite coatings

Boron nitride nanoplatelets (BNNPs) with excellent mechanical properties were introduced into HA coatings fabricated through plasma spray in this research. SEM observation and Raman results revealed the added BNNPs retained their original structure even after harsh process and distributed homogeneously in the as-sprayed coatings. As compared with the monolithic HA coating, a 2.0 wt%BNNP/HA coating exhibited significant improvement (~ 40.3%) in fracture toughness and moderate enhancement (~ 20.0%) in indentation yield strength. Synergetic strengthening and toughening mechanisms which are operative through splat boundaries and individual splats were proposed. At splat boundaries, these embedded BNNPs induced stronger adhesion between the adjacent splats to resist splat sliding, which is evident from the fact that the calculated inter-splat friction force of an as-sprayed BNNP/HA coating was increased by ~7.3% at 2.0% BNNP weight fraction. Within splats, toughening mechanisms such as BNNP pullout, crack bridging by both anchored BNNPs and nanosized HA grains, crack deflection and crack propagation arrested by the embedded BNNPs were observed to improve toughness. Moreover, thermal mismatch between HA matrix and BNNPs during cooling process after plasma spray would induce the pre-existing dislocations formed around these BNNP nanofillers, which was assumed to hold out the effect of Orowan-type strengthening within splats.

Hydrothermal Processing for Increasing the Hydroxyl Ion Concentration in Hydroxyl Depleted Hydroxyapatite

Thermal spraying is commercially used to produce hydroxyapatite coatings, but the high temperature depletes hydroxyl ions in the structure. To return hydroxyapatite to its original state, it is necessary to restore the hydroxyl ion content in the structure. In this work, the effect of hydrothermal treatment on the hydroxyl ions was investigated in hydroxyapatite powder and thermally sprayed hydroxyapatite coatings. Samples were hydrothermally treated at 200 °C for 24 h and 48 h. Chemical phases were determined by X-ray diffraction, functional groups and hydroxyl ion concentration was examined by Fourier transform infra-red spectroscopy. Results showed that hydrothermal processing of hydroxyapatite coatings at 200 °C for 48 hours produced the greatest increase in the hydroxyl ion concentration by 29%.

Study and Characterization of Mechanical and Electrochemical Corrosion Properties of Plasma Sprayed Hydroxyapatite Coatings on AISI 304L Stainless Steel

The use of hydroxyapatite coatings is limited by their inferior mechanical properties such as brittle nature, low wear resistance, abrasion, fatigue, and hardness. This ultimately leads to the wear and early rupture of the hydroxyapatite coating on the implant. The main objective of this study is to improve the mechanical properties of hydroxyapatite by using additional reinforcement material such as alumina (Al2O3). The HAp powder has been reinforced with 15wt% Al2O3 and its effect on the properties of HAp coatings has been studied. The HAp and HAp +15 wt% Al2O3 coatings were deposited on AISI 304 L SS substrates using the plasma spraying technique. The morphology of the coatings developed was characterized using SEM/EDX, XRD, and FTIR techniques. The corrosion resistance studies have been performed on uncoated and coated samples and found that HAp coated samples show superior resistance against corrosion (ICorr = 0.538 μA) than uncoated (ICorr = 3.550 μA) and HAp+15 wt% Al2O3 coated (ICorr = 1.440 μA) samples when electrochemical corrosion studies were performed in Ringer’s solution. Surface roughness and microhardness were found to increase with the addition of Al2O3. Crystallinity (%) of the HAp coatings and HAp+15 wt% Al2O3 coatings increases after the corrosion testing.

Flexural fatigue behavior of plasma-sprayed hydroxyapatite-coated polyether-ether-ketone (PEEK) injection moldings derived from dynamic mechanical analysis

Injection molded polyether-ether-ketone (PEEK) thermoplastic is often used for complex-shaped surgical implant applications, due to its elastic modulus compatibility with that of the human bone, excellent mechanical fatigue properties and biocompatibility. To enhance PEEK’s slow osteointegration, plasma sprayed hydroxyapatite (HA) coatings are mostly used. However, as the high temperatures related to the plasma process can induce additional surface residual compressive stresses in the molding, PEEK’s mechanical performance may be significantly impaired. In this study, using three distinct thermal conditions for PEEK: (i) “as molded”, (ii) plasma-exposed only and (iii) HA-coated, the influence of the plasma spray process was investigated on the fatigue behavior of PEEK under deformation-controlled three-point bending tests, monitored up to 106 cycles. The reduction verified in the fatigue stress decay rate indicates that the plasma thermal exposure contributes to a minor positive effect on the fatigue response of PEEK. Dynamic storage modulus (E′) and mechanical damping (tan δ) properties, determined by DMTA carried out in the prior-to and post-fatigue conditions, were useful to correlate the observed fatigue response to the additional surface residual compressive stresses and also to indicate that the fatigue induced “strain hardening” of PEEK is essentially restricted to the amorphous phase of the polymer.

Microstructural study of plasma sprayed hydroxyapatite coatings

Purpose: The aim of this study is to present microstructure and mechanical properties of hydroxyapatite coatings sprayed by means novel plasma system with axially injection of powder. Design/methodology/approach: Coatings were deposited with Axial III plasma spraying system and examined by SEM, XRD and by a nanoindentation technique (Nanovea) with a Berkovitz indenter. Surface of coatings was analysed by means of a Talysurf CCI-Lite non-contact 3D profiler. Findings: This study shows the microstructure and mechanical properties of hydroxyapatite coatings (HA) obtained by plasma spraying from the powder with a cauliflower-like high porous structure consisting of nanograins with dimension below 100 nm. The cross-section of plasma sprayed HA coating reveals lamellar structure containing pores in the interior of the lamellae. Moreover, between lamellae, some microcracks were detected. Hardness and elastic modulus measured by nanoindentation were found to be around 0.085 and 6.82 GPa respectively, what was comparable with HA coatings sprayed by a modified cold spray system. Both XRD patterns are practically identical, so no new phases were created in hydroxyapatite coating in comparison with feedstock powder during the spray process. High values of a geometry of HA coating; maximum peak height, maximum pit height and maximum height confirmed significant roughening of a surface, which is a result of the interaction of melted powder grains with the surfaces during the plasma spraying. Research limitations/implications: Obtained properties of coatings will be the base for comparison with suspension plasma sprayed coatings. Practical implications: Hydroxyapatite coatings deposited by means novel plasma system are designated for spraying implants. Originality/value: Properties of hydroxyapatite coatings plasma sprayed with novel axially injection of powder.

Investigation of the crystallinity of suspension plasma sprayed hydroxyapatite coatings

Hydroxyapatite coatings were deposited on stainless steel substrates. The arc current was varied to study its effect on the coating crystallinity. The crystallinity was calculated according to the XRD patterns via Jade 6.0 software and the full width at half maximum (FWHM) of Raman peak at 962cm−1. The FE-SEM images showed that HA coatings had rod-like nanostructures and agglomerated into microspheres. The XRD patterns indicated that the as-sprayed coatings were composed of HA and some decomposition phases. Micro-Raman spectroscopies demonstrated that the main phase in the coatings was HA. The results showed that the crystallinity was increased from 68.68% to 76.84% while the FWHM varied from 9.74 to 6.38cm−1, when the arc current increased from 400A to 600A. The selected area electron diffraction (SEAD) patterns were used to analyze the crystallinity qualitatively, and the results agreed with the conclusions of XRD and FWHM of Raman peak.

A comparative study on the synthesis and properties of suspension and solution precursor plasma sprayed hydroxyapatite coatings

In the present study, hydroxyapatite (HAp) coatings were deposited on Ti-6Al-4V alloy by solution precursor plasma spray (SPPS) and suspension plasma spray (SPS) processes and the properties of the coatings were compared. The feedstock powder for SPS method was prepared by coprecipitation technique and characterized for phase and morphology. The obtained HAp coatings were characterized by X-ray diffractometry, Raman spectroscopy and FT-IR spectroscopy. The biocompatibility of the coatings was evaluated using osteoblast like cells. Both the SPS and SPPS hydroxyapatite coatings exhibited similar crystallinity. Interestingly, the HAp-SPS coating showed marginally higher biocompatibility compared to HAp-SPPS and control samples. The wear and corrosion behavior of these coatings was also studied in Hanks' medium. The hydroxyapatite coating fabricated from SPS technique exhibited better corrosion and wear resistance compared to SPPS coating.