Comparative study of the hydroxyapatite coatings prepared with/without substrate bias

The aim of this paper is to prepare the hydroxyapatite by Ion Beam Assisted Deposition and to investigate in terms of its elemental and phase composition, roughness and in vitro corrosion resistance. The coatings were prepared with and without applying bias on substrate, in order to find the effect of bias on the chemical, structural, morphological and anti-corrosive properties. The biased coatings exhibited Ca/P ratio closer to the value of the stoichiometric HAP (1.67). The phase composition is not affected by the bias evolution. The adhesion of both coatings is still satisfactory for biomedical applications, irrespective of the bias. Hydroxyapatite deposited without bias presented the best corrosion resistance in SBF at 37 °C, probably due to its smooth surface and low porosity. Moreover, this coating proved to have the highest protection ability at the SBF corrosive attack.     

Characterization and corrosion behavior of plasma sprayed calcium silicate reinforced hydroxyapatite composite coatings for medical implant applications

Titanium and its alloys are widely used for medical implant applications, but their corrosion in the physiological environment leads to the discharge of metal ions, which can trigger severe health issues. In the present study, calcium silicate reinforced hydroxyapatite (HA-CS) coatings were deposited on the Ti6Al4V substrate by using atmospheric plasma spray (APS) process with an aim to improve the corrosion resistance and bioactivity. The coatings were prepared by varying the weight percentage (wt %) of calcium silicate (CS) reinforcement in hydroxyapatite (HA) as Ha/x CS (x = 0, 10, 20 wt %). The SEM analysis of the pure HA coating revealed the presence of surface microcracks, whereas HA-CS coatings displayed the crack-free surface morphology. The corrosion investigation revealed that with the progressive increment of CS content in HA coating, the corrosion resistance of HA-CS coatings improved. In addition, surface roughness, porosity, microhardness and crystallinity increased with the increase of CS content in HA. The findings of this study indicate that the development of plasma sprayed HA-CS coatings is a promising approach to improve the performance of Ti6Al4V alloy for medical implant applications.     

Influence of ionic substitution in improving the biological property of carbon nanotubes reinforced hydroxyapatite composite coating on titanium for orthopedic applications

The present work is aimed for the development of carbon nanotubes (CNTs) reinforced single mineral (Sr, Mg, Zn) as well as multi minerals (Sr+Mg+Zn) substituted hydroxyapatite composite (M-HAP) coatings on titanium (Ti). The effect of different mineral ions substitution and CNTs reinforcement in HAP composite coating is discussed in detail. Fourier Transform Infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM) equipped with energy dispersive X-ray analysis (EDX), and high resolution transmission electron microscopy (HRTEM) were used to characterize the structural and morphological behavior of the composite coatings. The corrosion resistance of the composite coatings in simulated body fluid (SBF) solution was evaluated by the potentiodynamic polarization and electrochemical impedance spectroscopic (EIS) studies. In addition, the biocompatibility of the composite coatings was evaluated by in vitro culture of human osteoblast MG63 cells on the composite coated Ti. All these results essentially suggest that CNTs/M-HAP composite coated Ti can be a potential candidate for orthopedic applications.     

在改性模拟体液中电沉积羟基磷灰石涂层

Hydroxyapatite coatings were directly prepared on anodized titanium by electro-deposition method in a modified simulated body fluid. The configuration, structure and bioactivity of the coating were investigated with scanning electron microscopy (SEM), X-ray diffraction analyzer (XRD) and Fourier transform infrared spectroscopy (FTIR) techniques. The results demonstrated that pure and homogeneous hydroxyapatite coating can be obtained without any post-treatment. The prepared coating showed good bioactivity in simulated body fluid (SBF). The time required for a fully covered dense hydroxyapatite coatings was 4 days immersion in SBF.     

Long-term corrosion resistance and fast mineralization behavior of micro-nano hydroxyapatite coated magnesium alloy in vitro

To improve the long-term corrosion resistance of biodegradable AZ31 magnesium alloy, the micro-nano structural hydroxyapatite (HA) coating was fabricated on AZ31 substrate by hydrothermal treatment. The compact and high crystallinity HA coating prepared at 120 °C had excellent electrochemical properties. Moreover, the cell viability experiment revealed that the micro-nano structure coating was conducive to the viability and proliferation of MC3T3-E1 osteoblasts. The immersion experiment in simulated body fluid (SBF) solution showed that the micro-nano structural HA coatings could quickly induce the production of HA mineralization, and then the mineralization evolved into a compact mineralized layer on the surface of coated sample, which provided a long-term protection for the specimen. Even after 147 days of immersion, the coated samples remained the relatively complete macroscopic shape, the corrosion rates were lower than 0.500 mm/y and the pH values of the SBF solution maintained in the range of 7.10–7.80, suggesting when these coated AZ31 magnesium alloys were used as degradable biomaterial implants, they could provide a long-term mechanical support during the healing of damaged bones.     

等离子体喷涂生物陶瓷涂层

综合介绍了文献及中国科学院上海硅酸盐研究所在等离子体喷涂生物涂层方面的近期研究进展。羟基磷灰石涂层已在临床上获得应用,但使用效果仍然受其较低的结合强度和结晶度所制约。通过优化喷涂工艺和制备羟基磷灰石基复合涂层,可有效提高羟基磷灰石涂层的结合强度和结晶度。此外,为了获得综合性能优良的植入体材料,制备了多种新型的生物活性陶瓷涂层。纳米氧化钛涂层经合适工艺的后处理可具有良好的生物活性,由于其与钛合金基体有较高的结合强度,在体液环境下具有高稳定性和生物相容性,使纳米氧化钛涂层成为一种具有发展前景的植入体涂层候选材料。新型生物活性硅酸钙涂层具有良好的生物活性,与骨组织能形成有效结合。此外,对这些新型涂层的生物活性机制也做了必要的描述。     

In vitro biocompatibility of a nanocrystalline β-Ta2O5 coating for orthopaedic implants

To improve the durability and bioactivity of Ti–6Al–4V alloy used for medical implants, the β-Ta₂O₅ nano-crystalline coatings were introduced using double cathode glow discharge technique. The coating microstructure was characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The coating exhibits an assembly of near-equiaxed grains, locally aligned normal to the coating surface. The β-Ta₂O₅ coating exhibits strong adhesion to substrate and a strong resistance to deformation and cracking under applied loads. Cells culture tests showed that the coating is more beneficial to the adhesion and proliferation of NIH-3T3 cells as compared to the uncoated alloy. In-vitro bioactivity was evaluated by immersion of the coating in simulated body fluids (SBF) for different periods up to 14 days at 37 °C. The results indicated that bioactivity of Ti–6Al–4V was dramatically improved after the deposition of β-Ta₂O₅, since the coating has a higher apatite forming ability than the Ti–6Al–4V substrate. Finally, the electrochemical behavior of the β-Ta₂O₅ coating after soaking in SBF at 37 °C for 0, 3, 7, and 14 days was studied through potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). EIS measurements also confirm that the presence of a hydroxyapatite layer on the coating becomes thicker and denser during soaking in SBF. Moreover, the coating exhibits better corrosion resistance than the bare alloy. Hence, the β-Ta₂O₅ coating is a promising candidate coating for protection of orthopedic implants with enhanced bioactivity and corrosion resistance.     

Fabrication and characterization of hybrid coating on Mg–Zn–Ca Mg alloy for enhanced corrosion and degradation resistance as medical implant

Magnesium (Mg)-based alloys have appealing properties as promising implants for medical applications. However, their clinical applications are hindered due to the rapid corrosion and degradation rate in the physiological environment. In this investigation, we reported a novel interfacial engineering approach for the fabrication of polymer/ceramic hybrid coating on Mg–Zn–Ca Mg alloy. Firstly, hydroxyapatite (HA) coating was fabricated on the Mg–Zn–Ca sample followed by an alkali treatment that was performed in 1 M NaOH solution at 60 °C. Finally, polycaprolactone (PCL) coating was synthesized using a dip-coating approach on the top of the HA-coated Mg–Zn–Ca specimen. Microhardness test and adhesion test revealed that PCL/HA hybrid coating significantly improved mechanical properties and enhanced biointerface property between the substrate and coating. The immersion tests showed that the hybrid coating considerably slowed down the degradation in the simulated body fluid (SBF) solution. In addition, in vitro electrochemical investigations confirmed that PCL/HA coating significantly improved corrosion resistance and greatly reduced corrosion rate by about 10 times compared to HA coating and about 900 times to untreated Mg–Zn–Ca sample. Moreover, cytotoxicity assessment exhibited PCL/HA hybrid coating enhanced biocompatibility and bioactivity due to adopting a suitable interfacial engineering approach.     

Evaluation of the protective nature of GO–BCP nanocomposite coatings on 316L SS in artificial body fluid

This work reports on a novel approach to deposit composite coatings based on biphasic calcium phosphate (BCP) incorporating graphene oxide (GO) on 316L stainless steel (316L SS) and on its protective nature against corrosion in the simulated body fluid (SBF). For this purpose, 2-dimensional GO was successfully incorporated in 1% and 3% weight ratios as mechanical strength enhancer and pore size reducer for the prepared coatings. It was observed that upon increasing the GO content, the corrosion rate was drastically decreased when compared to pristine BCP coating. The corrosion resistance polarization results are in good agreement with the test results obtained for SBF immersion study. The size of the particles has significantly decreased, as shown by transmission electron microscopy (from 190 to 27 nm). The experimental results indicate that the composite hydroxyapatite–β-tricalcium phosphate–GO (HAp–β-TCP–GO) coatings enhanced the corrosion resistance of the surgical grade 316L SS, turning it a better implanting option for orthopedic applications.     

Development of HA-CNTs composite coating on AZ31 Magnesium alloy by cathodic electrodeposition. Part 2: Electrochemical and in-vitro behavior

The carbon nano-tubes (CNTs) reinforced hydroxyapatite (HA), with various functionalized CNTs concentration ranging from 0 to 1.5?wt%, were deposited on AZ31 magnesium alloy by direct and pulse cathodic electrodeposition methods. The corrosion resistance of the coatings was tested in simulated body fluid (SBF) using different electrochemical methods such as open circuit potential, polarization and electrochemical impedance spectroscopy. The in-vitro behavior, changes in solution pH as well as the amount of evolved hydrogen of these coatings were also evaluated during five days immersion in SBF. The results indicated that the pulse deposited HA having 1% CNTs coating was the optimum condition which decreased the corrosion current density of AZ31 magnesium alloy from 44.25?µA/cm² to 0.72?µA/cm². Moreover, it stabilized the alkalization behavior of AZ31 alloy and caused a tenfold decrease in the amount of hydrogen generation in SBF. Additionally, the formation of new hydroxyapatite layer on the surface of the pre-exist coatings after five days immersion in SBF was confirmed by SEM characterization.     

Influence of strontium and niobium on the physical and biological performance of hydroxyapatite as a bioactive coating on implant materials

The coating of hydroxyapatite (HAP) on the surface of bio-inert metallic implants to augment their bioactivity is in use for the last two decades. Substitution of various materials in HAP further improves the functionality of these coatings. We demonstrate coating of Ti6Al4V alloy sheets with strontium and niobium reinforced HAP using microwave (MW) irradiation technique. Physical characterization revealed, uniform semicrystalline hydroxyapatite coating with enhanced surface roughness and microhardness. The increased surface roughness was accompanied by higher wettability and more protein adsorption. Electrochemical corrosion assessment showed a dramatic increase in corrosion potential and a noticeable decline in corrosion current density suggesting an enhanced anticorrosive behaviour. These implants also exhibited improved hemocompatibility and bacteriostatic properties. Cell viability and confocal microscopy studies of the coated samples showed enhanced cell attachment on the surface. We propose microwave irradiation as a fast and hassle-free alternative for one-pot synthesis and deposition of ionic substituted HAP on metallic implants.     

Strontium and copper co-substituted hydroxyapatite-based coatings with improved antibacterial activity and cytocompatibility fabricated by electrodeposition

Bacterial infection are serious complications for biomedical implants in the orthopedic and dental fields, and the ideal implants should combine good antibacterial ability and bioactivity. In this paper, we have fabricated the strontium/copper substituted hydroxyapatite (SrCuHA) coating on the commercially pure titanium (CP-Ti) and studied their effect on antibacterial and in vitro cytocompatible properties. Cu was incorporated into HA in order to improve its antimicrobial properties. Sr was added as a second binary element to improve the biocompatibility. The structural and morphological characteristics of the SrCuHA coatings were investigated using various analytical techniques. The presence of Sr²⁺ and Cu²⁺ in solution led to reduced roughness of the coating and finer nucleus size formed. The results highlight that Sr²⁺ and Cu²⁺ were homogenously incorporated into HA lattice to form SrCuHA coatings. Inductively coupled plasma mass spectrometry (ICP-MS) was used for the leach out analysis of the samples. A low contact angle value revealed the hydrophilic nature. In vitro electrochemical corrosion studies indicated that the SrCuHA coating sustain in the stimulated body-fluid (SBF), exhibiting superior corrosion resistance with a lower corrosion penetration rate than the bare CP-Ti substrate. The SrCuHA coatings can kill Escherichia coli to a certain extent during the first few days, which might be due to the Cu substitution in the coating. An enhancement of in vitro osteoblast adhesion, proliferation, and alkaline phosphatase activity was observed, which could lead to the optimistic orthopedic and dental applications.     

Robocasting and surface functionalization with highly bioactive glass of ZrO2 scaffolds for load bearing applications

This work is a proof of concept for making load bearing implants with osseointegration and bone bonding ability. Yttria-stabilized zirconia (YSZ) scaffolds with a percentage of macro porosity of about 70% were fabricated by robocasting. Although a maximum solids volume fraction of 50 vol.% could be achieved, the 3D-printing process revealed to be more reliable when using inks with 48 vol.% solids. The sintered porous structures exhibited an average compressive strength of ~236 MPa. After some preliminary coating experiments, an ethanol slurry of fine bioactive glass (BG) particles (10 wt.%) stabilized with polyvinylpyrrolidone was used to deposit a uniform surface coating onto the filaments, followed by glazing at 850°C. The functionalized scaffolds showed a relatively uniform surface coverage by the bioactive glass. The results of in vitro testing by immersing the scaffolds in simulated body fluid (SBF) showed remarkable morphological surface changes and an extensive deposition of hydroxyapatite layer. The overall results demonstrate the viability of producing porous YSZ scaffolds with excellent bioactivity, which are promising for bone tissue engineering under load bearing applications.     

等离子喷涂硅灰石涂层结构和性能的研究

采用等离子喷涂技术，在Ti-6Al-4V基体上制备了硅灰石涂层，利用SEM和XRD分析技术对涂层的形貌，结构和相组成进行了研究，按ASTMC－633标准对涂层的结合强度也进行了测试，将涂层试样浸泡于模拟体液中以评估其生物活性，利用SEM及配备的能谱仪（EDS），XRD和IR对浸泡后涂层表面产物的形貌，结构和相组成等进行了分析，结果表明，等离子喷涂硅灰石涂层具有粗糙的表面和层状结构，涂层内部存在一些气孔和微裂纹，涂层的主晶相是三斜晶系硅灰口，也存在玻璃相，硅灰石涂层和Ti-6Al-4V基体热膨胀系数相近，因此涂层和T-6Al-4V基体具有较高的结合强度，其值可达约39MPa，模拟体液浸泡试验显示，硅灰石涂层表面能形成含有碳酸根的羟基磷灰石层，这表明硅灰石涂层会有良好的生物活性，可作为生物活性涂层的候选材料。     

Electrodeposition of graphene oxide-hydroxyapatite composite coating on titanium substrate

In this work, graphene oxide (GO)/hydroxyapatite (HA) composite coatings were successfully prepared on titanium substrate by electrophoretic deposition technology. Subsequently, microstructure, phase composition, adhesion strength, hydrophilicity, corrosion resistance, bioactivity, antibacterial activity and biocompatibility of the coating were evaluated. The adhesion strength of coating increased by 76% from 6.46 MPa to 17.81 MPa with 0 wt% GO to 12 wt% GO and the corrosion rate of coating with 8 wt% GO was achieved at the minima of (1.493 × 10^-3mm/a). Biomineralization experiment indicated the excellent bioactivity of GO/HA composite coatings. The water contact angle of the composite coatings increased from 20.6°(0 wt% GO) to 38.1°(12 wt%GO). The antibacterial rates of coating with 5 wt% GO was 96.7%, while declined to 25% after thermal treatment. In-vitro L929 cell culture experiments indicated the composite coatings with 5 wt% GO exhibited good biocompatibility.     

Composite coatings of lanthanum-doped fluor-hydroxyapatite and a layer of strontium titanate nanotubes: fabrication,bio-corrosion resistance,cytocompatibility and osteogenic differentiation

Poor bio-corrosion resistance and undesirable incomplete osseointegration restrict the application of hydroxyapatite (HA) as an implant coating material. In this study, a novel F-and-La co-substituted hydroxyapatite (FLaHA) coating, which was reinforced with strontium titanate nanotubes (STNTs), was applied on Ti substrates using a combination method of anodization, electrochemical deposition and hydrothermal treatment. To the best of our knowledge, this is the first report on the development of FLaHA/STNT coatings for improving the chemical stability and the mechanical and biological properties of Ti substrates. The STNT exhibits an evenly-distributed porous and latticed structure on Ti substrates that favours the infiltration of FLaHA crystals. Different characterisation techniques, such as x-ray photoemission spectroscopy, x-ray diffraction, field-emission scanning electron microscopy and energy-dispersive spectroscopy, have clearly confirmed the successful synthesis of STNT-FLaHA coatings that constitute oriented nanorod arrays. Isolated hexagonal nanorod grains, with diameters of 200–300?nm, that stand on a substrate provide a uniform morphology to the surface of electrodeposited thin films at micro-scales. The survival of the coatings was prolonged because of their good degradation resistance. Owing to the anchoring effect of the STNT layer, the adhesion strength of the FLaHA/STNT coating was 15.9?±?5.4?MPa, which was two times higher than that of STNT-free HA coatings. The potentiodynamic polarisation curves and the Nyquist plot confirmed that the conversion coating significantly improved the bio-corrosion resistance of the Ti substrates in the SBF solution. Roughness and hydrophilicity of the control HA layer were even greater than those of the FLaHA/STNT coating. However, it provided better cell adhesion, spreading, proliferation and osteogenic differentiation for mouse pre-osteoblasts cells. That is, the FLaHA/STNT coating could enhance osteoconductivity by improving the cell-adhesion, proliferation and differentiation of osteoblast. Therefore, FLaHA/STNT nanocomposite coatings can be used as implant materials with multi-functional properties, such as good biocompatibility and high mechanical and corrosion-inhibiting properties.     

Preparation and bioactivity of apatite coating on Ti6Al4V alloy by microwave assisted aqueous chemical method

To improve the bioactivity of titanium and its alloys, dense and uniform apatite coatings were prepared on Ti6Al4V titanium substrates using microwave assisted aqueous chemical method. The influence of the pretreatment to the titanium substrates and the Ca/P molar ratio of the microwave solution on the coating deposition and morphology, as well as the bioactivity of the coated samples were studied. Results showed that during the microwave process, alkali treatment followed by heat treatment to the titanium substrates would promote the rapid deposition of hydroxyapatite to form coating. And the morphologies of the apatite coatings could be adjusted by the Ca/P molar ratio of the microwave solution. After immersion test in simulated body fluid (SBF), the coated titanium alloy exhibits a good bioactivity by inducing the formation of apatite depositions.     

Deposition temperature effect on sputtered hydroxyapatite coatings prepared on AZ31B alloy substrate

The corrosion of Mg alloys is a provocative topic and it is still a challenge to find a solution for the improvement of their degradation rate into solution found in human body (Simulated Body Fluid, SBF). The aim of the present paper is to coat AZ31B alloy by hydroxyapatite (HAp) as a possible solution in order to change its degradation behaviour for medical implants. Since the Mg alloy is sensible to temperature while the HAp properties depend on the deposition temperature, in this study, the effect of deposition temperature on the properties of the AZ31Balloy was evaluated. The HAp coatings were prepared using the RF magnetron sputtering technique, ranging the temperature from the room one to 400 °C. It was found that the grain size of the investigated Mg alloy increased more than 100% when the deposition temperature was increased. By increasing the temperature, the hardness level was reduced of about 15%. All HAp coatings revealed corrosion behaviour much better than the uncoated AZ31B alloy; in particular, the coating deposited at 200 °C exhibited the best corrosion behavior. Moreover, the best protection to the corrosive attack of SBF was found for the HAp coating deposited at 200 °C (97.3%), which was also characterized by the lowest porosity. To conclude, HAp coatings can be used to improve the properties of AZ31B alloys, but just up to 200 °C; beyond this temperature, the mechanical and the anticorrosion properties are lost.     

Preparation and characterization of hydroxyapatite-forsterite-bioactive glass nanocomposite coatings for biomedical applications

In order to improve biological and mechanical properties of hydroxyapatite, the concept of hydroxyapatite-included nanocomposite coatings was introduced. By judiciously choosing constituent ceramics for composites preparation, the biological and mechanical performance of coatings can be tailored in order to meet various clinical requirements. The aim of this work was fabrication, development and characterization of novel hydroxyapatite-forsterite-bioactive glass nanocomposite coatings. The sol-gel technique was used to prepare hydroxyapatite-forsterite-bioactive glass nanocomposite in order to apply coating on 316L stainless steel (SS) by dip coating technique. The X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX) were used to investigate the phase structure, microstructure and morphology of the coating. In order to evaluate the forsterite incorporation influence upon bioactivity, the changes on the surfaces of the prepared composite coatings after the predicted days of contact with simulated body fluid (SBF) were investigated by SEM. Results showed that the suitable calcined temperature for nanocomposite coatings with different amounts of forsterite was 600 °C. At this temperature, the homogenous and crack-free coating could attach to the 316L SS substrate. The crystallite sizes of the prepared coatings were lower than 100 nm. The EDX analysis of hydroxyapatite-forsterite-bioglass, coated 316L SS surface, indicated consisting elements of prepared coatings and the substrate. During immersion in the SBF at pre-determined time intervals, apatite layer was formed and stimulation for apatite formation was increased with increase in forsterite amounts. It seems that hydroxyapatite-forsterite-bioactive glass nanocomposite coatings might be good candidates for biomedical applications.     

Corrosion behaviour of plasma sprayed graphene nanoplatelets reinforced hydroxyapatite composite coatings in simulated body fluid

Hydroxyapatite (HA) coatings, reinforced with varied concentration (0–2 wt%) of Graphene nanoplatelets (GNPs) have been deposited on titanium alloys (Ti–6Al–4V) substrate using atmospheric plasma spraying. Present work studies the effect of GNP concentration on the electrochemical behaviour of the HA coatings in simulated body fluid (SBF). The HA coating exhibited 15% porosity, whereas reinforcement of 1 wt% GNPs in HA (HA-1G) shows 13% porosity, further addition of 2 wt% GNPs in HA reduced the porosity to 10%. Reduction in porosity was achieved as GNPs easily accessed the inter-lamellae to fill the gaps at inter splat region and minimized the occurrence of post-plasma spray defects such as porosity, voids, microcracks etc. These consequences nextward resulted in the significant enhancement in corrosion resistance of the matrix. HA-1G displayed a significant reduction by 67% in the corrosion rate in SBF solution, while this reduction came to 87% for HA-2G coatings. Randomly oriented wrinkles in the GNPs after corrosion process and their hydrophobic nature effectively hindered the SBF infiltration into the coating and resisted their movement towards the underlying substrate. This in turn improved the overall corrosion resistance of the system.