Electrophoretic deposition of hydroxyapatite coatings on titanium from dimethylformamide suspensions

Hydroxyapatite powders were prepared by a chemical precipitation method and electrophoretically deposited on pure Ti surgical substrates. The powders were suspended in dimethylformamide (DMF). The zeta potential, electromobility and the conductivity of the HA suspension was characterized at various pH values to identify the most stable dispersion conditions. The effect of applied voltage and deposition time on deposition rate, deposition thickness and coating morphology were studied. The coating morphology and composition were characterized by scanning electron microscopy (SEM). The crystalline phase of HA before and after electrophoretic deposition was examined using X- ray diffraction (XRD). Transition electron microscope (TEM) indicated that HA consisted of needle-shaped crystallites.     

Preparation and characterization of silicon-substituted hydroxyapatite coating by a biomimetic process on titanium substrate

A biomimetic method has been used to prepare silicon-substituted hydroxyapatite coatings on titanium substrates. The surface structures of the coatings were characterized by X-ray diffraction, X-ray photoelectron spectroscopy (XPS) and Fourier transformed infrared spectroscopy (FTIR). Si substituted hydroxyapatite (Si-HA) coatings with different Si contents were deposited successfully on the titanium substrate by immersing the pretreated titanium substrate into silicon containing supersaturated solutions (SSS) with different SiO₃²⁻ concentrations. The pretreatment of the Ti substrate in a mixed alkaline (NaOH + Ca(OH₂)) followed by a heat treatment produced a 3D porous surface structure with rutile and CaTiO₃ as main phases, which contributed mainly to the fast precipitation and deposition of Si-HA. FTIR results showed that Si in the Si-HA coating existed in the form of SiO₄⁴⁻ groups. The cross-section microstructure was observed by scanning electronic microscopy and the shear strength was tested. The coating was about 5-10 μm in thickness and no interval was observed at the interface between the coating and the substrate. Shear strength testing showed that Si-HA/Ti exhibited higher shear strength than HA/Ti due to the existence of the SiO₄⁴⁻ group in the coating.     

Hydroxyapatite coating on titanium substrate by electrophoretic deposition method: Effects of titanium dioxide inner layer on adhesion strength and hydroxyapatite decomposition

Nanosized hydroxyapatite (HA) powders were prepared by a chemical precipitation method and electrophoretically deposited on Ti6Al4V substrates. The powders were calcined before the deposition process in order to obtain crack-free coating surfaces. As an inner layer between Ti6Al4V substrate and HA coating, nanosized titanium dioxide (TiO₂) powders were deposited, using different coating voltages, in order to connect substrate and HA tightly. Moreover, this layer is considered to be acting as a diffusion barrier, reducing the HA decomposition due to ion migration from the metal substrate into the HA. After the sintering stage, adhesion strengths of coatings were measured by shear testing, phase changes were studied by X-ray diffraction, and coating morphology was analyzed through scanning electron microscopy observations. Results showed that usage of the TiO₂ inner layer prevented HA decomposition. Furthermore, decreasing the voltage used in TiO₂ deposition resulted in crack-free surfaces and increased adhesion strength of the overall coating.     

Novel hydroxyapatite coating on new porous titanium and titanium-HDPE composite for hip implant

Porous titanium (Ti) and Ti-high density polyethylene (Ti-HDPE) composite were investigated as new hip implant materials to increase the biomechanical compatibility by promoting a matching modulus of elasticity between hip stem and human bone. Surfaces of both materials were modified to increase its bioactivity and biocompatibility through electrochemical activation treatment and deposition of hydroxyapatite (HA) coating. The electrochemical activation treatment of both materials in 10 M NaOH solution created a bone-like porous nanostructure across the surfaces, thus enhancing the growth of natural bone. A top layer with nanometer-pores and TiO₂ was formed during the activation process, creating a favorable and prerequisite condition conducive to the formation of hydroxyapatite coating. Furthermore, a layer of hydroxyapatite, a bioactive and biocompatible bioceramics that is the main component of natural bone, was deposited on the porous Ti and Ti-HDPE composite through a novel chemo-biomimetic method. The formed coating was characterized through TEM as a nanometer scale crystalline.     

New method for hydroxyapatite coating of titanium by the hydrothermal hot isostatic pressing technique

A new hydrothermal method is proposed, which enables us to prepare thin hydroxyapatite (HA) ceramic coatings on Ti substrates with a curved surface at low temperatures. The method uses double layered capsules in order to produce a suitable hydrothermal condition; the inner capsule encapsulates the coating materials and a Ti substrate, and the outer capsule is subjected to isostatic pressing under the hydrothermal condition. In this study, it is demonstrated that a pure HA ceramic layer with the thickness of 50 μm could be coated to a Ti cylindrical rod at the low temperature as low as 135 °C under the confining pressure of 40 MPa. The HA coating layer had a porous microstructure with the relative density of approximately 60%. Pull-out tests were conducted to obtain an estimate for the adhesion properties of the HA coating prepared by the double capsule method. The shear strength obtained from the pull-out tests was in the range of 4.0–5.5 MPa. It was also shown that the crack propagation occurred within the HA coating layer, not along the HA/Ti interface in the pull-out tests. This observation suggests that the fracture property of the HA/Ti interface was close to or higher than that of the HA ceramics only. It is expected that the low temperature double capsule method may provide a useful method for producing bioactive HA ceramic coatings on curved prostheses surfaces.     

Preparation and in vitro biocompatibility of hybrid oxide layer on titanium surface

A new technique combining microarc oxidation (MAO) and electrophoresis was introduced to develop a biocompatible oxide layer on pure titanium implant surface. Originally developed alkaline electrolyte containing nano-scale hydroxyapatite powder suspension was used in the new technique. In the electric field, nano-scale hydroxyapatite powder was electrophoretically moved and sintered into the gradually-formed oxide layer on titanium anode. Physio-chemical properties and in vitro biological performance of the newly-formed surface were examined and evaluated. A 8.5-μm thick oxide layer with high surface energy and roughness, which was composed of titanium dioxide and calcium phosphates as well as hydroxyapatite, was formed on titanium surface by the modified MAO technique. Osteoblasts cultured on the modified MAO titanium surface showed significantly increased alkaline phosphatase (ALP) activity comparing to machined and MAO titanium surface. Natural oxide surface of titanium could be transformed into a hybrid oxide layer by modified MAO treatment. The modified titanium surface, which is rough and porous, contains calcium phosphates and proved to be more biocompatible in vitro.     

Laser-assisted laser ablation method for high-quality hydroxyapatite coating onto titanium substrate

Hydroxyapatite (HAp) coating on titanium (Ti) or Ti alloy implant materials is one of the important technologies for improving the bioactivity of their surface. We recently developed a new HAp coating method using two laser beams, laser-assisted laser ablation method (LALA method). In this method, two excimer lasers were used. One laser beam from KrF laser, the ablation laser, is used for ablation of a HAp target. The other beam from ArF laser, the assist laser, is used to irradiate a Ti substrate surface during formation of the HAp coating. The assist laser plays an important role in the formation of a crystalline HAp coating and improves the strength of adhesion to the Ti substrate.The coating quality varied with the timing of the assist laser irradiation. A coating deposited with a long assist laser delay contained a large amorphous component. High-quality coatings were obtained with delay time between 2 and 10 μs.Using the present method, we succeeded in fabricating thin (≤1 μm) HAp coatings with high crystallinity and high adhesion strength.     

Adhesion of sol-gel derived hydroxyapatite nanocoatings on anodised pure titanium and titanium (Ti6Al4V) alloy substrates

The mechanical properties and adhesion behaviour of sol-gel derived hydroxyapatite (HA) nanocoatings on commercially pure (cp) titanium (Ti) and Ti6Al4V alloy have been determined and related to anodising treatment. The surface roughness, wetting and coating characteristics were examined using profilometry, contact angle, scanning electron microscopy (SEM) and X-ray diffraction (XRD). Nano-indentation was used to determine the Young's modulus and hardness of the coatings, while microtensile tests were used to introduce controlled strains in the coatings through the cp Ti and TiAl6V4 alloy substrates, from which the strength, fracture toughness and adhesion behaviour could be ascertained based on multiple cracking and delamination events. The toughness of the HA coatings is found to be slightly lower to that of equivalent bulk pure HA ceramics. The substrate and the anodized layer thickness have the most influence on the interfacial adhesion of HA, with nanocoatings on Ti6Al4V exhibiting superior interfacial bonding in comparison to cp Ti.     

Effects of the electric conditions of AC-type microarc oxidation and hydrothermal treatment solution on the characteristics of hydroxyapatite formed on titanium

This study examined the effects of the conditions for AC-type microarc oxidation (MAO) and the type of hydrothermal treatment solution on the characteristics of hydroxyapatite(HAp)-containing oxide films deposited on commercially pure titanium (CP-Ti). The MAO treatments were carried out in an electrolyte containing 0.2 M calcium acetate monohydrate and 0.02 M β-glycerophosphoric acid disodium salt pentahydrate (β-GP) using AC-type rectangular electric pulses at different voltages and frequencies. HAp formation on the surface of the MAO-treated group was induced by a hydrothermal treatment in either an alkaline solution to form HT-treated groups or a 0.002 M β-GP solution (pH = 11.0) to produce HTP-treated groups. A mixed crystalline structure consisting of anatase TiO₂, rutile TiO₂ and CaTiO₃ was observed on the MAO-treated groups treated with a low frequency and voltage. When the AC frequency was increased, anatase TiO₂ became the dominant crystalline structure and there was an even distribution of pores. HAp particles were formed more densely on the HTP-treated groups than on the HT-treated groups. Among the HTP groups, the groups fabricated at higher frequencies contained more evenly distributed and crystallized HAp crystallites.     

Development of carbon nanotubes reinforced hydroxyapatite composite coatings on titanium by electrodeposition method

Carbon nanotubes (CNTs) are outstanding reinforcement material for imparting strength and toughness to brittle hydroxyapatite (HAP). This work reports the electrodeposition of CNTs reinforced HAP on titanium substrate at −1.4 V vs. SCE during 30 min with the functionalised CNTs concentration ranging from 0 to 2 wt.%. Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM) equipped with energy dispersive X-ray analysis (EDX), high resolution transmission electron microscopy (HRTEM), mechanical and biological studies were used to characterise the coatings. Also, the corrosion resistance of the coatings was evaluated by electrochemical techniques in simulated body fluid (SBF) solution.     

Synthesis and characterization of sol-gel hydroxyapatite coatings deposited on porous NiTi alloys

A hydroxyapatite (HA) coating was deposited onto a porous NiTi alloy via dip-coating using a sol-gel procedure with triethyl phosphite and calcium nitrate as phosphorus and calcium precursors, respectively. Adjusting the concentration and viscosity of the sol as well as changing the spin-coating rotational velocity or dip-coating times, enabled uniform coatings with controllable thickness at the sub-micron scale to be successfully deposited on the external surface and within the pores of the porous NiTi alloy. Cross-sectional SEM analysis and EDS characterization of the HA films show that the coating on the inner surface of the pores is thicker than that on the outer surface. The results of an immersion test in a Tris solution show that the HA coating possesses excellent stability, and the rates of Ni ion release through the HA coatings on the porous NiTi alloys of different porosity ratios in a simulated body fluid decrease markedly compared with the uncoated alloys. There is also a remarkable increase in the apatite forming ability of the HA coated porous NiTi alloy in a calcium containing solution.     

Alternative technique for hydroxyapatite coatings

Flame Assisted Chemical Vapor Deposition (FACVD), a novel technique that shows an enormous potential in porous oxides deposition, was employed for the first time aiming to obtain hydroxyapatite (HA) coatings on 316 L stainless steel metallic substrates. Calcium acetate and ammonium phosphate diluted in ethanol were employed as precursor salts. A Ca/P molar ratio of 1.66 was employed in precursor solution, which is equivalent to stoichiometric hydroxyapatite. A porous coating, formed by an open and interconnected network, was observed by scanning electronic microscopy (SEM) and associated with homogenous reactions. Thickness of hydroxyapatite coating was 412 ± 3 μm. X-ray diffraction (XRD) analysis indicated the presence of crystalline coatings, mainly constituted by hydroxyapatite phase and traces of tricalcium phosphate (β-TCP). Carbonate in the hydroxyapatite coatings was identified by Fourier transform-infrared (FTIR) spectroscopy.     

Electrochemical deposition of hydroxyapatite coatings on titanium

1 Introduction Titanium implants have been used widely for various types of bone-anchored reconstructions due to their excellent corrosion resistance and mechanical properties. However, titanium exhibits poor osteoinductive properties, fortunately, which…     

Nanoindentation reveals mechanical properties within thermally sprayed hydroxyapatite coatings

Nanoindentation offers a unique capability to assess the mechanical properties of polished cross-sections of thermal spray coatings. This study set out to investigate the suitability of nanoindentation to extend the analysis of the cross-section to multiple points for a more detailed insight into variations through the thickness of the coating. Hydroxyapatite (HAp) was classified to three different particle sizes (20-40, 40-60 and 60-80 μm) and then thermally sprayed to produce a structurally homogeneous coating. Micro-Raman Spectroscopy (MRS) revealed dehydroxylation of the powder during the traverse in the thermal zone. Multiple indentations with a separation of 4 μm showed a transition within the thickness of the coating. Use of smaller particles led to higher hardness and elastic modulus compared to powder containing larger particles. The mechanical property profile provides valuable information for optimizing the processing of such coatings and feedback for the design of coating properties.     

Microstructural characterization of NiCr1BSiC laser clad layer on titanium alloy substrate

Laser cladding of NiCrBSiC powders on Ti–6Al–4V alloy substrate was carried out, and the microstructure of the laser clad layer was characterized by TEM and SEM. Results show that the phases of TiC, TiB₂, CrB and M₂₃C₆ were formed in situ in the clad layer. The TiC phase exists in the form of dendrites with two types of interface morphology including the non-faceted and the faceted one. The TiB₂ phase nucleates on the facets of TiC dendrites, and can grow to form a special morphology of microstructure in which the TiC dendrite is encased by the TiB₂ phase. The CrB and M₂₃C₆ phases exist in the form of rod-shaped morphology, inside which stacking faults could be observed. The clad layer matrix consists of primary γ_p-Ni dendrites and lamellar eutectics of γ_e-Ni+Ni₃B. The formation mechanism of the microstructure of the clad layer was discussed.     

Experimental design of plasma spraying and laser treatment of hydroxyapatite coatings

Plasma spray process of hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, HA) followed by laser treatment of obtained coatings were optimized by an advanced statistical planning of experiments. The full factorial design of 2⁴ experiments was used to find effects of four principal parameters, i.e. electric power, plasma forming gas composition, carrier gas flow rate and laser power density onto microstructure of hydroxyapatite (HA) coatings and powders and depth of laser melted zone. The SAS and Statgraphics commercial softwares have been applied to obtain the mathematical model of influence of process parameters onto experimental responses. The chosen responses were the fraction of HA crystal phase and two phases of its decomposition α-tricalcium phosphate (Ca₃(PO₄)₂, α-TCP), tetracalcium phosphate (Ca₄P₂O₉, TTCP) and, on the other hand, the depth of laser melted zone in the coating. The two most important factors influencing these responses are electric power supplied to torch, laser power density. Laser power density is very important for the depth of laser melted zone. The crystal phase content of powders and coatings was determined using X-ray diffraction (XRD) quantitative analysis. The morphologies of coatings surfaces, cross-sections were characterized using scanning electron microscope (SEM).     

Preparation and characterisation of electrophoretically deposited hydroxyapatite coatings on type 316L stainless steel

Hydroxyapatite (HAP) coatings were developed on type 316L stainless steel (SS) by electrophoretic deposition at various deposition potentials from 30 to 90 V using the stoichiometric HAP (Ca/P ratio 1.67) powder in a suspension of isopropyl alcohol. The optimum coating parameters were established at 60 V and 3 min, after vacuum sintering at 800 °C. The phase purity of the coated surface was confirmed by XRD and secondary ion mass spectrometry confirmed the presence of both Ca and P on the coated layers. The electrochemical corrosion parameters E_corr (open circuit potential) and pitting potentials, evaluated in Hank’s solution shifted towards noble direction for the HAP coated specimens in comparison with uncoated type 316L SS. Electrochemical impedance spectroscopic investigations revealed higher polarisation resistance and lower capacitance values after immersing the coated specimens in Hanks solution for 200 h. This indicates the stable nature of the coatings formed.     

电沉积制备氧化石墨烯-羟基磷灰石复合涂层

采用电沉积方法在钛表面制备氧化石墨烯-羟基磷灰石(Graphene oxide/Hydroxyapatite,GO/HA)复合涂层,通过调整GO的浓度,研究GO对所得涂层晶体结构及生物学性能的影响。采用扫描电镜(SEM)、透射电镜(TEM)、X射线衍射(XRD)仪、傅里叶变换红外光谱(FTIR)、拉曼光谱分析所得涂层的表面形貌和物相构成,用SEM观察涂层表面MG63成骨样细胞生长情况。结果表明,电沉积法可在钛表面制备GO/HA复合涂层,且随GO浓度增加,HA结晶度增加。此外,复合涂层较单纯HA涂层更能促进成骨样细胞早期粘附。     

Effect of a bioactive glass-ceramic on the apatite nucleation on titanium surface modified by micro-arc oxidation

The aim of this work was to evaluate the ability of a bioactive glass-ceramic to induce the apatite nucleation on the titanium oxide layer produced by micro-arc oxidation. “In vitro” tests were carried out on a simulated body fluid solution in two different manners: one group was soaked in the SBF, while the other group was soaked together with the bioactive glass-ceramic. Results revealed that after 7 days, the specimens soaked in SBF were covered with an amorphous calcium phosphate layer, while the specimens soaked in SBF plus glass-ceramic formed a crystalline apatite layer, suggesting thus, that the glass-ceramic provides silanol groups that accelerated the hydroxyapatite apatite precipitation on the anodic TiO₂ layer.     

热处理和SBF浸泡对羟基磷灰石涂层力学性能的影响

利用X射线衍射仪（XRD）、电子探针（EPMA）、扫描电镜（SEM）等检测手段，研究了等离子喷涂羟基磷灰石（HA）涂层热处理前后的显微组织变化，以及经热处理和模拟体液（SBF）浸泡处理对涂层力学性能的影响。结果表明：涂层内部衬度不一，存在化学非均匀性。涂层中的裂纹、气孔、未熔颗粒界面是断裂的起源。热处理能使涂层中的不均匀性消失，成分趋于一致，结晶度提高。热处理后，粗颗粒涂层结合强度升高而细颗粒涂层则降低。0．5SBF浸泡处理后，所有涂层的结合强度都降低，原始细颗粒涂层降低幅度最大，原始粗颗粒涂层次之，热处理细涂层降低幅度最小。