In situ composite coating of titania-hydroxyapatite on titanium substrate by micro-arc oxidation coupled with electrophoretic deposition processing

In situ composite coating of hydroxyapatite (HA)/TiO₂ were produced on titanium (Ti) substrate by micro-arc oxidation coupled with electrophoretic deposition (MAO&EPD) technique with different concentrations of HA particles in the 0.2 M NaOH electrolyte solution. The surface morphology and chemical composition of the hybrid coating were effected by HA concentration. The amount of HA particles incorporated into coating layer increased with increasing HA concentration used in the electrolyte solution. The corrosion behavior of the coating layer in simulated body fluids (SBF) was evaluated using a potentiodynamic polarization test. The corrosion resistance of the coated sample was increased compared to the untreated Ti sample. The in vitro bioactivity assessment showed that the MAO&EPD treated Ti substrate possessed higher apatite-forming ability than the untreated Ti. Moreover, the apatite-forming ability had a positive correlation with HA concentration. In addition, the cell behavior was also examined using cell proliferation assay and alkaline phosphatase ability. The coating formed at HA concentration of 5 g/L exhibited the highest cell ability.     

Preparation of an electrodeposited hydroxyapatite coating on titanium substrate suitable for in-vivo applications

In this paper the porous hydroxyapatite coating on Ti implant materials was prepared by the process of electrodeposition, hydrothermal and sinter. The surface morphology, bond strength and thickness of HA coatings were investigated by SEM, AFM, and its biocompatibility was evaluated by cytotoxicity experiments and implant experiments, respectively. Results showed that (1) The HA coatings was 50 μm thickness and adhered on the Ti substrate strongly, which bond strength reached 38MPa. AFM analysis showed that the HA coating was porous structure, in which the mean pore size was 236.5 μm, (2) Cytotoxicity experiments and implant experiments showed that HA-coated Ti implant materials has little cytotoxicity in vitro and little inflammatory reaction in vivo, and there were no statistically disparity between HA-coated Ti implant and titanium implant materials of clinical application (p > 0.05), which demonstrated that HA-coated Ti has a good biocompatibility.     

Characteristics and mechanical properties of a (Ti, O, N)/Ti composite coating fabricated on NiTi shape memory alloy via PIIID

In this investigation, (Ti, O, N)/Ti composite coating was fabricated on a NiTi shape memory alloy (SMA) to improve its biocompatibility, bioactivity and wear resistance for its long-term medical applications, using the plasma immersion ion implantation and deposition (PIIID) technique. Scanning electron microscopic (SEM) examination of coating cross-sections showed that the (Ti, O, N)/Ti composite coating was uniform and compact. Energy dispersive X-ray (EDX) analysis not only indicated that the interface between the coating and NiTi SMA substrate was gradual rather than sharp, but it also showed the thickness of the composite coating to be ∼ 1.0 μm. The EDX mapping of cross-sections of (Ti, O, N)/Ti composite coating revealed that Ni was not present on the surface of the coated samples. Nanoindentation tests were performed to evaluate mechanical properties of the composite coating. Pin-on-disc wear test results showed greatly improved wear resistance of (Ti, O, N)/Ti coated NiTi SMA.     

Bioactive nanocomposite coatings of collagen/hydroxyapatite on titanium substrates

Collagen/hydroxyapatite (HA) nanocomposite thin films containing 10, 20, and 30 wt.% HA were prepared on commercially pure titanium substrates by the spin coating of their homogeneous sols. All of the nanocomposite coatings having a thickness of ∼7.5 μm exhibited a uniform and dense surface, without any obvious aggregation of the HA particles. A minimum contact angle of 36.5° was obtained at 20 wt.% HA, suggesting that these coatings would exhibit the best hydrophilicity. The in vitro cellular assays revealed that the coating treatment of the Ti substrates favored the adhesion of osteoblast-like cells and significantly enhanced the cell proliferation rate. The cells on the nanocomposite coatings expressed much higher alkaline phosphatase (ALP) levels than those on the uncoated Ti substrates. Increasing the amount of HA resulted in a gradual improvement in the ALP activity. The nanocomposite coatings on Ti substrates also exhibited much better cell proliferation behaviors and osteogenic potentials than the conventional composite coatings with equivalent compositions, demonstrating the greater potential of the former as implant materials for hard tissue engineering.     

Silicon-substituted hydroxyapatite composite coating by using vacuum-plasma spraying and its interaction with human serum albumin

The incorporation of silicon can improve the bioactivity of hydroxyapatite (HA). Silicon-substituted HA (Ca₁₀(PO₄)_6−x (SiO₄) _x (OH)_2−x , Si-HA) composite coatings on a bioactive titanium substrate were prepared by using a vacuum-plasma spraying method. The surface structure was characterized by using XRD, SEM, XRF, EDS and FTIR. The bond strength of the coating was investigated and XRD patterns showed that Ti/Si-HA coatings were similar to patterns seen for HA. The only different XRD pattern was a slight trend toward a smaller angle direction with an increase in the molar ratio of silicon. FTIR spectra showed that the most notable effect of silicon substitution was that –OH group decreased as the silicon content increased. XRD and EDS elemental analysis indicated that the content of silicon in the coating was consistent with the silicon-substituted hydroxyapatite used in spraying. A bioactive TiO₂ coating was formed on an etched surface of Ti, and the etching might improve the bond strength of the coatings. The interaction of the Ti/Si-HA coating with human serum albumin (HSA) was much greater than that of the Ti/HA coating. This might suggest that the incorporation of silicon in HA can lead to significant improvements in the bioactive performance of HA.     

ZrO2/hydroxyapatite coating on titanium by electrolytic deposition

In this study, hydroxyapatite (HA) was coated on a titanium (Ti) substrate over a ZrO(2) layer by the electrolytic deposition method, this double layer coating was then compared with a single layer coating of HA. The HA layer was used to increase the bioactivity and osteoconductivity of the Ti substrate, and the ZrO(2) layer was intended to improve the bonding strength between the HA layer and Ti substrate, and to prevent the corrosion of the Ti substrate. The electrolytic deposition formed an HA layer with a thicknesses of approximately 20 mum, which adhered tightly to the Ti substrate. The bonding strength of the HA/ZrO(2) double layer coating on Ti was markedly improved when compared to that of the HA single coating on Ti. The improvement in bonding strength with the use of a ZrO(2) base layer was attributed to the resulting increase in chemical affinity of the ZrO(2) to the HA layer and to the Ti substrate. The osteoblast-like cells cultured on the HA/ZrO(2) coating surface, proliferated in a similar manner to those on the HA single coating and on the pure Ti surfaces. At the same time, the corrosion resistance of Ti was improved by the presence of the ZrO(2) coating, as shown by a potentiodynamic polarization test.     

Novel hydroxyapatite/tantalum surface coating for metallic dental implant

The aim of this study was to design and produce a novel surface composite coating on metallic substrate in order to improve the biocompatibility of metallic dental implant and the bone osteointegration simultaneously.Stainless steel 316L (SS) was used as a metallic substrate and a novel double-layer hydroxyapatite/tantalum (HA/Ta) coating was prepared on it. Tantalum coating was made using physical vapor deposition process and HA coating was produced using plasma-spraying technique on it. X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques were utilized to investigate the coating characterization. Electrochemical polarization tests were performed in two types of physiological solutions at 37 ± 1 °C in order to determine the corrosion behavior of the coated and uncoated specimens as indication of biocompatibility.The results indicated that the decrease in corrosion current density was significant for HA/Ta coated specimens and was much lower than the value obtained for uncoated 316L SS. The novel double-layer HA/Ta composite coating could improve the corrosion resistance and thus the biocompatibility of 316L SS dental implant.     

等离子喷涂HA/Ti复合涂层研究 I.结构、组成和力学性能

采用等离子喷涂方法,在Ｔｉ－６Ａｌ－４Ｖ基体上成功地制备了ＨＡ／Ｔｉ复合涂层,并对复合涂层的微观结构、相组成和力学性能进行了研究．结果表明,ＨＡ和Ｔｉ两相均匀地分布于复合涂层中．ＨＡ／Ｔｉ复合涂层的结合强度明显高于纯 ＨＡ涂层,这主要是由于 ＨＡ／Ｔｉ的复合缓和了涂层与基体之间的热膨胀系数失配．ＨＡ／Ｔｉ复合涂层在模拟体液中浸泡一段时间后,结合强度没有明显降低．ＨＡ／Ｔｉ复合涂层的断裂韧性和硬度均高于 ＨＡ涂层．     

Fabrication of nano-structured HA/CNT coatings on Ti6Al4V by electrophoretic deposition for biomedical applications

In order to improve the bone bioactivity and osteointegration of metallic implants, hydroxyapatite (HA) is often coated on their surface so that a real bond with the surrounding bone tissue can be formed. In the present study, cathodic electrophoretic deposition (EPD) has been attempted for depositing nanostructured HA coatings on titanium alloy Ti6Al4V followed by sintering at 800 degrees C. Nano-sized HA powder was used in the EPD process to produce dense coatings. Moreover, multiwalled carbon nanotubes (CNTs) were also used to reinforce the HA coating for enhancing its mechanical strength. The surface morphology, compositions and microstructure of the monolithic coating of HA and nanocomposite coatings of HA with different CNT contents (4 to 25%) on Ti6Al4V were investigated by scanning-electron microscopy, energy-dispersive X-ray spectroscopy and Xray diffractometry, respectively. Electrochemical corrosion behavior of the various coatings in Hanks' solution at 37 degrees C was investigated by means of open-circuit potential measurement and cyclic potentiodynamic polarization tests. Surface hardness, adhesion strength and bone bioactivity of the coatings were also studied. The HA and HA/CNT coatings had a thickness of about 10 microm, with corrosion resistance higher than that of the substrate and adhesion strength higher than that of plasma sprayed HA coating. The properties of the composite coatings were optimized by varying the CNT contents. The enhanced properties could be attributed to the use of nano-sized HA particles and CNTs. Compared with the monolithic HA coating, the CNT-reinforced HA coating markedly increased the coating hardness without deteriorating the corrosion resistance or adhesion strength.     

Hydroxyapatite-anatase-carbon nanotube nanocomposite coatings fabricated by electrophoretic codeposition for biomedical applications

In order to eliminate micro-cracks in the monolithic hydroxyapatite (HA) and composite hydroxyapatite/carbon nanotube (HA/CNT) coatings, novel HA/TiO₂/CNT nanocomposite coatings on Ti6Al4V were attempted to fabricate by a single-step electrophoretic codeposition process for biomedical applications. The electrophoretically deposited layers with difference contents of HA, TiO₂ (anatase) and CNT nanoparticles were sintered at 800°C for densification with thickness of about 7–10 μm. A dense and crack-free coating was achieved with constituents of 85 wt% HA, 10 wt% TiO₂ and 5 wt% CNT. Open-circuit potential measurements and cyclic potentiodynamic polarization tests were used to investigate the electrochemical corrosion behavior of the coatings in vitro conditions (Hanks’ solution at 37°C). The HA/TiO₂/CNT coatings possess higher corrosion resistance than that of the Ti6Al4V substrate as reflected by nobler open circuit potential and lower corrosion current density. In addition, the surface hardness and adhesion strength of the HA/TiO₂/CNT coatings are higher than that of the monolithic HA and HA/CNT coatings without compromising their apatite forming ability. The enhanced properties were attributed to the nanostructure of the coatings with the appropriate TiO₂ and CNT contents for eliminating micro-cracks and micro-pores.     

等离子喷涂HA/Ti复合涂层研究 I.结构、组成和力学性能

采用等离子喷涂方法,在Ｔｉ－６Ａｌ－４Ｖ基体上成功地制备了ＨＡ／Ｔｉ复合涂层,并对复合涂层的微观结构,相组成和力学性能进行了研究。结果表明,ＨＡ和Ｔｉ两相均匀地分布于复合涂层中。ＨＡ／Ｔｉ复合涂层的结合强度明显高于纯ＨＡ涂层,这主要是由于ＨＡ／Ｔｉ的复合和了涂层与基体之间的热膨胀系数失配,ＨＡ／Ｔｉ复合涂层在模拟体液中浸泡一段时间后,结合强度没有明显降低,ＨＡ／Ｔｉ复合涂层的断裂韧性和硬度均高于Ｈ     

Growth and characterization of hydroxyapatite nanorice on TiO2 nanofibers

Hydroxyapatite (HA) coating with nanoparticles like nanorice is fabricated on chemically pretreated titanium (Ti) surface, through an electrochemical deposition approach, for biomaterial applications. The Ti surface was chemically patterned with anatase TiO₂ nanofibers. These nanofibers were prepared by in situ oxidation of Ti foils in a concentrated solution of H₂O₂ and NaOH, followed by proton exchange and calcinations. Afterward, TiO₂ nanofibers on Ti substrate were coated with HA nanoparticles like nanorice. The obtained samples were annealed at high temperature to produce inter diffusion between TiO₂ and HA layers. The resultant layers were characterized by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), X-ray Photoelectron Spectroscopy (XPS), X-ray Diffraction (XRD), Infrared Spectroscopy (FTIR), corrosion tests in SBF solution, and Electron Probe Micro Analysis (EPMA). It was found that only Ti from the titanium substrate diffuses into the HA coating and a good corrosion resistance in simulated body fluid was obtained.     

Effect of titanium and titania on chemical characteristics of hydroxyapatite plasma-sprayed into water

HA and its composite particles (HA/Ti, HA/TiO₂) were plasma-sprayed into water as well as on the Ti substrate, respectively. The microstructure and phase compositions of the sprayed HA and its composite particles before and after impinging on the substrate were studied by using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy. The results showed that the HA in the composite particles sprayed into water had a higher crystallinity than that in the composite coating. The addition of Ti or TiO₂ could both influence the decomposition of HA, but no chemical reacting product between them was formed before and after impinging on the substrate. However, EDS analyses showed the occurrence of interdiffusion of elements between HA and TiO₂, which was favorable to enhance the cohesive strength of particles in the composite coating. The post heat treatment at 650 °C for 2 h can effectively improve the crystallinity of coating by transforming amorphous phases into HA.     

Surface characteristics of hydroxyapatite/titanium composite layer on the Ti-35Ta-xZr surface by RF and DC sputtering

The purpose of this study was to investigate the surface characteristics of hydroxyapatite (HA)/titanium (Ti) composite layer on the Ti-35Ta-xZr alloy surface by radio frequency (RF) and direct current (DC) sputtering for dental application. The magnetron sputtered deposition for the HA was performed in the RF mode and for the Ti in the DC mode. Microstructures of the alloys were examined by optical microscopy (OM) and x-ray diffractometer (XRD). Surface characteristics of coated film was investigated by field-emission scanning electron microscope (FE-SEM) equipped with an energy dispersive x-ray spectrometer (EDS), and XRD. Microstructures of the Ti-35Ta-xZr alloys were changed from α″ phase to β phase, and changed from a needle-like structure to an equiaxed structure with increasing Zr content. From the results of polarization behavior in the Ti-35Ta-15Zr alloy, HA/Ti composite layer showed the good corrosion resistance compared to Ti single layer. The results of alternating current (AC) impedance test indicated that the presence of ha coating acted as a stable barrier in increasing the corrosion resistance.     

Surface characterization of colloidal-sol gel derived biphasic HA/FA coatings

Hydroxyapatite (HA) powders are ultrasonically dispersed in the precursor of fluoridated hydroxyapatite (FHA) or fluorapatite (FA) to form a “colloidal sol”. HA/FA biphasic coatings are prepared on Ti6Al4V substrate via dip coating, 150 °C drying and 600 °C firing. The coatings show homogenous distribution of HA particles in the FA matrix. The relative phase proportion can be tailored by the amount of HA in the colloidal sol. The surfaces of the coatings consist of two kinds of distinct domains: HA and FA, resulting in a compositionally heterogeneous surface. The biphasic coating surface becomes increasingly rougher with HA powders, from around 200 nm of pure FA to 400–600 nm in Ra of biphasic coatings. The rougher biphasic HA/FA surfaces with chemically controllable domains will favor cell attachment, apatite layer deposition and necessary dissolution in clinical applications.     

沉积温度对多孔钛表面仿生制备羟基磷灰石的影响

为研究沉积温度对羟基磷灰石涂层生长的影响,制备了不同温度条件下成分恒定的仿生沉积液,并采用纯钛和不同孔径的多孔钛做基体,在其表面仿生沉积羟基磷灰石涂层,再将得到的涂层试样浸泡在标准模拟体液中检测其生物活性.通过X射线衍射仪(XRD)分析涂层物相结构,用金相显微镜、环境扫描电子显微镜(ESEM)表征涂层形貌,利用能谱分析仪(EDS)计算钙磷比.研究表明:基体孔径增大,有利于沉积液进入到孔隙且表面粗糙度相对增大,从而使得HA涂层变得均匀致密;沉积温度由30℃升高至37℃,会加快HA涂层致密均匀的生长,但温度升高到44℃时,HA晶粒变粗大,涂层变得疏松化;模拟体液浸泡后,Ti/HA涂层试样表面有新的HA生成,且Ca/P比接近标准的1.67,表明该Ti/HA涂层试样具有良好的生物活性.适当增大钛基体孔径,提高沉积液温度,可以得到均匀致密的HA生物活性涂层.     

Effects of duty ratio at high frequency on growth mechanism of micro-plasma oxidation ceramic coatings on Ti alloy

The aim of this work is to study the effects of duty ratio on the growth mechanism of the ceramic coatings on Ti–6Al–4V alloy prepared by pulsed single-polar MPO at 2,000 Hz in NaAlO₂ solution. The phase composition of the coatings was studied by X-ray diffraction, and the morphology and the element distribution in the coating were examined through scanning electron microscopy and energy dispersive spectroscopy. The thickness of the coatings was measured by eddy current coating thickness gauge. The corrosion resistance of the coated samples was examined by linear sweep voltammetry technique in 3.5% NaCl solution. Duty ratio influenced the composition and structure of the coatings. Many residual discharging channels on the coating surface showed that the spark discharge at 2,000 Hz was mainly attributable to the breakdown of the oxide film, which was suitable for the elements both from the electrolyte and from the substrate to join MPO process, and therefore, the coating was mainly composed of Al₂TiO₅. Because of the increase of the congregation and the adsorption of Al from the electrolyte with increasing duty ratio, the redundant Al on the electrode surface led to the formation of γ-Al₂O₃. And Al and Ti in the coating existed in the form of the reverse gradient distribution. Meantime, ceramic coatings improved the corrosion resistance of Ti alloy, and the coating surface morphology and thickness determined the coated samples prepared at D = 20% had the best corrosion resistance among the coated samples.     

Microstructures and bond strengths of plasma-sprayed hydroxyapatite coatings on porous titanium substrates

Hydroxyapatite (HA) coating was carried out by plasma spraying on bulk Ti substrates and porous Ti substrates having a Young’s modulus similar to that of human bone. The microstructures and bond strengths of HA coatings were investigated in this study. The HA coatings with thickness of 200–250 μ m were free from cracks at interfaces between the coating and Ti substrates. XRD analysis revealed that the HA powder used for plasma spraying had a highly crystallized apatite structure, while the HA coating contained several phases other than HA. The bond strength between the HA coating and the Ti substrates evaluated by standard bonding test (ASTM C633-01) were strongly affected by the failure behavior of the HA coating. A mechanism to explain the failure is discussed in terms of surface roughness of the plasma-sprayed HA coatings on the bulk and porous Ti substrates.     

Silver doped hydroxyapatite coatings by sacrificial anode deposition under magnetic field

Uniform distribution of silver (Ag) in the hydroxyapatite (HA) coated Ti surface has been a concern for which an attempt has been made to dope Ag in HA coating with and without magnetic field. Cathodic deposition technique was employed to coat Ag incorporated hydroxyapatite coating using a sacrificial silver anode method by using NdFeB bar magnets producing 12 Tesla magnetic field. While uniform deposition of Ag was observed in the coatings under magnetic field, dense coating was evident in the coating without magnetic field conditions. Uniformly distributed Ag incorporated HA in the present study has potential to fight microorganism while providing osseoconduction properties of the composite coating.     

三维钛网表面双生物陶瓷涂层的制备及其性能

采用浸渍涂敷-烧结法首次在医用三维钛网表面制备出双生物陶瓷涂层,利用X射线衍射、场发射扫描电子显微镜对HA-BG/BG/Ti复合材料进行了微观表征,拉伸法测量了Ti基体与BG涂层的结合强度,模拟人体体液(SBF)评价复合材料的生物相容性.研究表明:该双生物陶瓷涂层的内层为生物玻璃(BG)涂层,外层为多孔结构的羟基磷灰石-生物玻璃(HA-BG)复合涂层.Ti基体被致密的BG涂层包覆,由于在BG/Ti界面发生化学反应,界面的结合强度提高,平均结合强度达27 MPa.生物相容性实验表明,HA-BG/BG/Ti复合材料表面会被一层整齐、致密的HA覆盖,具有良好的生物相容性.