Fabrication of Ti/TiO2(Ca)/hydroxyapatite bioceramic material by micro-arc oxidation and electrochemical deposition

Titanium with a bioceramic hydroxyapatite (HA) coating has been widely used in biomaterials owing to its excellent mechanical characteristics and high osteoconductivity. However, the interfacial strength of Ti/HA prepared by electrochemical deposition (ED) is relatively low because the physical combination is typically inadequate. In this study, to improve the interfacial strength, a micro-arc oxidation (MAO) process with calcium was introduced for preparing a connecting interlayer known as the MAO coating. Pulsed ED was employed to synthesise the HA coating on the MAO surface using an electrolyte with 6 wt% H₂O₂. Sample characterisations revealed that the MAO coating comprised porous TiO₂ (rutile and anatase) with Ca or CaTiO₃. The formation of CaTiO₃ depends on the current density, reaction time, and concentration of Ca²⁺, in addition to voltage. The MAO coatings exhibited a higher corrosion resistance than that exhibited by Ti substrates. Furthermore, the HA coating on the MAO coating was confirmed to be plate-like Ca-deficient HA. The final sample had a Ti/TiO₂(Ca)/HA structure, and its adhesive strength was approximately double that of the Ti/HA sample. In particular, the MAO coating synthesised at a high Ca²⁺ concentration exhibited an improved adhesive strength (2.326 MPa). The application of the MAO coating containing Ca as a connecting interlayer is a promising strategy for improving the HA adhesion strength.     

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.     

Effect of graphene reinforcement on hybrid bioceramic coating deposited on the produced porous Ti64 alloys

Porous-Ti64 alloys (P-Ti64), produced at various porosities by hot-pressing technique with the help of Mg spacer, were coated by hybrid-Graphene Oxide (rGO) reinforced-hydroxyapatite (HAp), using the sol–gel method. The synthesized rGO powder was used in reinforcing HAp by the Modified Hummers method having 30 µm particle size and nano (nm) scale layer thickness. Hybrid coatings were executed on Ti64 substrates in four different groups as single-HAp, HAp reinforced with 0.5 wt%, 1.0 wt% and 1.5 wt% rGO for three different porosities (41, 52, and 64%) were characterized by FT-IR, Raman, XRD and SEM. The average 21 µm coating film thicknesses were obtained and desirably, the only superficial pores of the substrates were closed by coating material rather than the inner connected open pores. It was also shown that 0.5 wt% and 1.0 wt% rGO reinforcements into HAp prevented crack formation on the Ti64 surfaces, whereas 1.5 wt% rGo reinforcement and single-HAp coatings caused. The highest adhesion strength values were achieved at low porosities (41–52%) and of 0.5–1.0 wt% rGO reinforcements through the adhesion tests.

     

Biomimetic apatite deposited on microarc oxidized anatase-based ceramic coating

Biomimetic apatite was formed on a microarc oxidized (MAO) anatase-based coating containing Ca and P in a simulated body fluid (SBF). At the process of the SBF immersion (0–96 h), the Ca and P of the MAO coating dissolve into the SBF, increasing the supersaturation degree near the surface of the MAO coating, which could promote the formation and growth of apatite. After SBF immersion for 7 days, the surface of the MAO coating was modified slightly. The entire surface immersed for 14 days was covered by an apatite coating. The apatite possesses carbonated structure, controllable crystallinity and pore networks. The results indicate that the MAO coating formed in an electrolyte containing phosphate and EDTA–Ca chelate complex possesses good apatite-forming ability.     

Improvement in corrosion resistance of micro-arc oxidation coating on PVD Ti-coated aluminum alloy 7075

Surface treatments are always needed to enhance corrosion-resistant performance of aluminum (Al) alloys when they are used in seawater environments. The paper aimed to prepare the composite oxide ceramic coating on Al alloy 7075 by combining micro-arc oxidation (MAO) and magnetron sputtering technology. The Al substrate was precoated with titanium (Ti) layer by using the magnetron sputtering technology and then treated by MAO in the alkaline aluminate electrolyte, resulting in a composite MAO coating, which is composed of Al₂O₃ and TiO₂ along with the complex oxide (Al₂TiO₅). The potentiodynamic polarization and electrochemical impedance spectroscopy were carried out to evaluate the corrosion performance of the MAO coatings in 3.5 wt% NaCl solution. Better corrosion resistance was observed for composite oxide coating than the reference MAO coating on the bare Al, as evidenced by the higher corrosion potential of −0.664 V versus Ag/AgCl and the lower corrosion current density of 4.41 × 10^-6 A/cm².     

Surface,Biocompatible and Hemocompatible Properties of Meta‐Amorphous Titanium Oxide Film

This study involved modification of the surface of Ti by micro‐arc oxidation (MAO). A rough and porous oxide film with good wettability was formed on the Ti surface. This MAO‐treated film exhibited a meta‐amorphous structure comprising crystalline anatase and rutile TiO₂ as well as amorphous phases. In addition, the incorporation of Ca and P in the MAO‐treated film was induced by micro‐arc discharge. The biological responses of the MAO‐treated surfaces were evaluated by observing the adhesion of MG63 osteoblast‐like cells and platelets. The MAO‐treated Ti had a considerably better biocompatibility and blood compatibility than untreated Ti.     

Micro-arc oxidation of bioceramic coatings containing eggshell-derived hydroxyapatite on titanium substrate

In the present study eggshells-derived hydroxyapatite (EHA) coatings were successfully produced on Ti6Al4V substrates using micro-arc oxidation process (MAO) at various concentrations of EHA (i.e. 1, 1.5 and 2 g/L) in an electrolyte consisting of tri-sodium orthophosphate. The attributes of the coatings were determine by X-ray diffraction, attenuated total reflectance-fourier transform infrared spectroscopy, field emission scanning electron microscopy and energy dispersive X-ray spectroscopy. The adhesion strength was evaluated using micro scratch tester, while the corrosion behavior of the MAO-coated substrates in phosphate buffer solution was determined by an electrochemical method. The results showed that as the EHA concentration increased, this was accompanied by a reduction in the porosity due to the formation of a dense and thick coating layer. This has also resulted in an increased in the surface roughness and degree of crsytallinity of the HA phase. The MAO-coated substrate prepared with 1.5 g/L EHA concentration exhibited a well-formed coating layer with improved adhesive strength and excellent corrosion resistance. The mechanism of EHA-coating formation as well as the enhanced corrosion resistance of the coated substrates were discussed. This research shows the viability of using calcium-rich waste eggshells to produce phase pure HA suitable for coating on Ti6Al4V substrate using MAO method.     

Preparation,biomimetic apatite induction and osteoblast proliferation test of TiO2-based coatings containing P with a graded structure

TiO₂-based coatings containing P (T–P) were prepared on Ti6Al4V by microarc oxidation (MAO) with applied voltages of 200–400 V in an electrolyte containing (NaPO₃)₆ and NaOH. The surfaces of the T–P coatings became rough and the thickness increased with increasing the applied voltage. Above 200 V, anatase was found on the surface, and rutile was observed at 400 V. With increasing the coating thickness, the O and P concentrations increase; while Ti and Al concentrations decrease. Ti, O and P elements display a uniform distribution character around the micropores on the surface of the T–P coating formed at 300 V. However, the inner of the micropores exhibits a high Ti concentration and low O and P concentrations due to the graded distributions of Ti, O and P elements in the T–P coating. The apatite-forming ability of the T–P coating formed at 300 V was evaluated by immersing in a simulated body fluid (SBF) for 28 and 56 days. The results indicate that biomimetic apatite was formed on the surface of the T–P coating after immersion in SBF for 56 days. And the further cell experiment indicates that the T–P coating can provide surface suitable for the MG63 cell proliferation.     

Characterisation of in-situ reactive plasma-sprayed nano-(Ti,V)N composite ceramic coatings with various V concentrations

The effect of V concentration on the microstructure and phase composition of nano-(Ti, V)N composite ceramic coatings prepared by in-situ reactive plasma spraying of mechanically mixed Ti–V powders were investigated using X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, X-ray energy dispersive spectroscopy, and transmission electron microscopy. The microhardness, toughness, wear resistance, and strengthening mechanism of the prepared nano-(Ti, V)N coatings were measured and analysed. The results showed that the nano-(Ti, V)N coating comprised a large proportion of nano-(Ti, V)N grains, which was the solid solution of TiN and VN. All the V atoms completely entered the TiN lattice and the solubility limit of V in TiN is approximately 25 wt%. The grains of the (Ti, V)N (25 wt% V) coating had a face-centred cubic structure and a large quantity of twins; they were primarily equiaxed grains morphology with a few columnar grains. From comparing the experimental statistics, the (Ti, V)N (25 wt% V) coating displayed the highest microhardness (1952 ± 78.5 Hv) and the most even dispersion but a slightly lower toughness compared with the (Ti, V)N (35 wt% V) coating. The (Ti, V)N (25 wt% V) coating with a dense microstructure obtained a high microhardness due to dislocation strengthening, fine grain strengthening, and solid solution strengthening (from the solid solution of VN in TiN). Furthermore, a lower friction coefficient and wear volume loss indicated that the (Ti, V)N (25 wt% V) coating had superior tribological properties and great potential as a wear resistant coating.     

Sol-gel-derived hydroxyapatite-carbon nanotube/titania coatings on titanium substrates

In this paper, hydroxyapatite-carbon nanotube/titania (HA-CNT/TiO(2)) double layer coatings were successfully developed on titanium (Ti) substrates intended for biomedical applications. A TiO(2) coating was firstly developed by anodization to improve bonding between HA and Ti, and then the layer of HA and CNTs was coated on the surface by the sol-gel process to improve the biocompatibility and mechanical properties of Ti. The surfaces of double layer coatings were uniform and crack-free with a thickness of about 7 μm. The bonding strength of the HA-CNT/TiO(2) coating was higher than that of the pure HA and HA-CNT coatings. Additionally, in vitro cell experiments showed that CNTs promoted the adhesion of preosteoblasts on the HA-CNT/TiO(2) double layer coatings. These unique surfaces combined with the osteoconductive properties of HA exhibited the excellent mechanical properties of CNTs. Therefore, the developed HA-CNT/TiO(2) coatings on Ti substrates might be a promising material for bone replacement.     

High-performance self-healing anticorrosion epoxy coating based on microencapsulated epoxy-amine chemistry

Attributed to the merits of excellent material compatibility, healing performance, and long-term stability, the self-healing system based on microencapsulated epoxy-amine chemistry is a potentially practical self-healing system for both structural and functional materials. Herein, based on the microencapsulated epoxy-amine chemistry, a self-healing anticorrosion coating was successfully developed. This self-healing coating system was modeled theoretically to explore the factors that influence the crack filling and the self-healing anticorrosion function. The established quantitative relationship shows that the filling depth of the crack in the coating is proportional to the microcapsule parameters and coating thickness, but inversely proportional to the crack width. Based on the above theoretical model, the effects of various parameters on the anticorrosion performance were experimentally studied. The actual filling of small in-situ cracks (<100 μm) generated by impact damage was semi-quantitatively characterized using scanning electron microscopy (SEM). The filling behavior is consistent with the theoretical modeling. After being healed at room temperature for 2 days upon impact damage, the formulated self-healing coatings were subjected to accelerated corrosion tests in 10 wt% sodium chloride (NaCl) solution for 2 days to observe their anticorrosion behavior. Compared to the neat epoxy coating, all the formulated self-healing epoxy coatings show evident anticorrosion function. Good self-healing anticorrosion performance was achieved by adding 10.0 wt% microcapsules with a size of 100–150 μm to the coating with a thickness of 300 μm. The results of this investigation laid a theoretical and technical foundation for the further development of both the self-healing chemistry and the self-healing anticorrosion coating.     

Vacuum Plasma Spray Deposition of Titanium Particle/Glass-Ceramic Matrix Biocomposites

The vacuum plasma spray technique (VPS) has been successfully employed to coat Ti-6A1-4V substrates with bioactive glasses and Ti-particle/glass-ceramic matrix biocomposites. The composites were prepared by sintering, under an Ar flow, green bars of bioactive glass powders and 30% volume Ti particles. The bioactive glasses have the two following compositions: SCB (48.8SiO₂−48.8CaO−2.4B₂O₃) and TSCB (46.6SiO₂−48.7CaO−2.5B₂O₃−2.2TiO₂) (mol%). The VPS bioactive coatings were characterized by means of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and mechanical tests (Vickers indentations and tensile and shear tests). Their bioactivity was tested by soaking the samples in a simulated body fluid (SBF) and by analyzing the growth of hydroxylapatite (HA) by SEM, EDS, and XRD. Leaching tests of Ca, Si, and P in SBF were made by inductively coupled plasma-atomic emission spectroscopy (ICP-AES, Perkin-Elmer 5000) to study the in vitro bioactivity of the samples versus time. Each coating was found to be bioactive and well bonded to the substrate; the composites showed better mechanical properties than the pure glass matrices and the hydroxylapatite coatings deposited by the same VPS technique.     

The Potential of Calcium/Phosphate Containing MAO Implanted in Bone Tissue Regeneration and Biological Characteristics

Micro arc oxidation (MAO) is a prominent surface treatment to form bioceramic coating layers with beneficial physical, chemical, and biological properties on the metal substrates for biomaterial applications. In this study, MAO treatment has been performed to modify the surface characteristics of AZ31 Mg alloy to enhance the biocompatibility and corrosion resistance for implant applications by using an electrolytic mixture of Ca₃(PO₄)₂ and C₁₀H₁₆N₂O₈ (EDTA) in the solutions. For this purpose, the calcium phosphate (Ca-P) containing thin film was successfully fabricated on the surface of the implant material. After in-vivo implantation into the rabbit bone for four weeks, the apparent growth of soft tissues and bone healing effects have been documented. The morphology, microstructure, chemical composition, and phase structures of the coating were identified by SEM, XPS, and XRD. The corrosion resistance of the coating was analyzed by polarization and salt spray test. The coatings consist of Ca-P compounds continuously have proliferation activity and show better corrosion resistance and lower roughness in comparison to mere MAO coated AZ31. The corrosion current density decreased to approximately 2.81 × 10⁻⁷ A/cm² and roughness was reduced to 0.622 μm. Thus, based on the results, it was anticipated that the development of degradable materials and implants would be feasible using this method. This study aims to fabricate MAO coatings for orthopedic magnesium implants that can enhance bioactivity, biocompatibility, and prevent additional surgery and implant-related infections to be used in clinical applications.     

Fabrication of corrosion resistant, bioactive and antibacterial silver substituted hydroxyapatite/titania composite coating on Cp Ti

The present work is aimed at developing a bioactive, corrosion resistant and anti bacterial nanostructured silver substituted hydroxyapatite/titania (AgHA/TiO₂) composite coating in a single step on commercially pure titanium (Cp Ti) by plasma electrolytic processing (PEP) technique. For this purpose 2.5 wt% silver substituted hydroxyapatite (AgHA) nanoparticles were prepared by microwave processing technique and were characterized by X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectroscopy and transmission electron microscopy (TEM) methods. The as-synthesized AgHA particles with particle length ranging from 60 to 70 nm and width ranging from 15 to 20 nm were used for the subsequent development of coating on Cp Ti. The PEP treated Cp Ti showed both titania and AgHA in its coating and exhibited an improved corrosion resistance in 7.4 pH simulated body fluid (SBF) and 4.5 pH osteoclast bioresorbable conditions compared to untreated Cp Ti. The in vitro bioactivity test conducted under Kokubo SBF conditions indicated an enhanced apatite forming ability of PEP treated Cp Ti surface compared to that of the untreated Cp Ti. The Kirby-Bauer disc diffusion method or antibiotic sensitivity test conducted with the test organisms of Escherichia coli (E. coli) for 24 h showed a significant zone of inhibition for PEP treated Cp Ti compared to untreated Cp Ti.     

Characteristic, cell response and apatite-induction ability of microarc oxidized TiO2-based coating containing P on Ti6Al4V before and after chemical-treatment and dehydration

The structure, cell response and induction capability for apatite formation of the microarc oxidized (MAO) coating before and after chemical-treatment and subsequent dehydration at 400 °C were investigated. The surfaces of the chemically treated MAO (C-MAO) coatings before and after dehydration showed ribbon-like amorphous phase mainly containing Na, Ti and O elements with network morphology. Subsequent dehydration has no pronounced effect on the surface roughness, wetting ability, surface constituents and chemical state of Ti, Na and O of the C-MAO coating. The outer layers of the C-MAO coating before and after dehydration showed Na, Ti and O elements with uniform distributions along the surface depth. Chemical-treatment improves the apatite-forming ability of the MAO coating; however, subsequent dehydration greatly lowers that of the C-MAO coating, since it changed the ability of C-MAO coating to release Na⁺ ions, which is unfavorable for the formation of Ti-OH groups. The apatite formed on the two coatings contained HPO₄²⁻ and CO₃²⁻ ions. In addition, the dehydration of the C-MAO coating seemed to be unsuitable for the cell proliferation on its surface.     

Barium titanate-based bilayer functional coatings on Ti alloy biomedical implants

Piezoelectric coatings have the ability to functionalise conventional structural materials into responsive devices. Today, piezoelectric coatings have been applied to both rigid and flexible substrates for sensing, actuating, and energy harvesting applications. We envision (Ba,Ca)(Zr,Ti)O₃ (BCZT) piezoelectric coatings for biomedical use such as in vivo sensing or electrical cell stimulation. However, reliable processing routes for the development of BCZT ceramics as a functionalisation coating on biomedical substrates are required. In this work, the synthesis of bilayer BCZT and CaTiO₃ ceramic coatings on Ti6Al4V metal substrates via spray-deposition and heat-treatment was investigated. For thin coatings, reactions at the metal/ceramic interface led to the development of a porous interface reaction region partly consisting of CaO. The hygroscopicity of CaO affects the adhesion of the coating to Ti6Al4V at ambient conditions. Minimisation of the kinetic contributions to these interface reactions were achieved by increasing the coating thickness.     

Hydroxyapatite Coating on Thermally Oxidized Titanium Substrates

Titanium substrates were oxidized in oxygen or air at temperatures of 600°–800°C, then immersed in solutions of 2.0m M – 20.7m M CaCl₂ and 1.2m M –12.4m M KH₂PO₄ for aging periods of 0.5–10 d. The titanium surface was successfully coated with hydroxyapatite (HAP) when the substrates were oxidized in oxygen gas at 610°C for 1 h and then aged in a solution of 2.00m M Ca²⁺ and 1.20m M PO₄³⁻. The Ca/P ratio of the surface coating increased toward its stoichiometric HAP value (return 10/6) as the aging time increased; the Ca/P ratio attained a value of 1.66 after 10 d.     

Wettability of Silica Substrates by Silver–Copper Based Brazing Alloys inVacuo

The sessile drop method has been used to determine the time dependence of the contact angle at 850°C in vacuo for Ag–28 wt% Cu, Ag–35 wt% Cu–1.5 wt% Ti, and Ag–27 wt% Cu–12 wt% In–2 wt% Ti on vitreous and devitrified fused quartz substrates. Nonwetting behavior (θ > 90°) was observed for Ag–28 wt% Cu on both substrates with no evident effect of time at temperature. The silica substrate structure, whether crystalline or amorphous, as well as its surface condition, whether smooth or rough, made no significant difference. In contrast, with Ag–35 wt% Cu–1.5 wt% Ti and Ag–27 wt% Cu–12 wt% In–2 wt% Ti the contact angle continuously decreased with time for both silica substrates, and the structure and surface condition of the substrates had a negligible effect in the case of Ag–27 wt% Cu–12 wt% In–2 wt% Ti, which produced essentially the same contact angles on both silica substrates at a given time of hold at 850°C. The contact angles produced by Ag–35 wt% Cu–1.5 wt% Ti on devitrified fused quartz were consistently higher than those produced on the vitreous substrates, with increasing holding time at 850°C. This is attributable to the presence of extensive cracks in the α-cristobalite layer at the surface of the devitrified substrates, which obstruct wetting and spreading. These results, when correlated with the wettability of preoxidized silicon carbide by the same alloys reported in previous work, could account for the adverse effect on wetting of the high-temperature silica films formed on the surface of the SiC in that work.     

Electrochemical effects of silane pretreatments containing cerium nitrate on cathodic disbonding properties of epoxy coated steel

In the recent years, silane materials, because of their environmental friendly nature and ease of application have been attended as an alternative for chromate conversion coatings. Different materials were searched for improvement of the efficiency of silane formulation. In this research, pretreatment of carbon steel substrates was carried out using γ-glycidoxypropyl-trimethoxysilane (γ-GPS) as functionalized silane. Cerium nitrate as a corrosion inhibitor material was introduced into the silane material and epoxy resin was applied on the pretreated steel substrates. Effects of the pretreatment on electrochemical properties, cathodic disbondment, dry and wet adhesion strength, and surface morphology of resultant epoxy coating were investigated. Results showed that pretreatment of steel substrate with γ-glycidoxypropyl-trimethoxysilane (γ-GPS) doped with cerium nitrate leads to improvement of cathodic disbondment and also dry and wet adhesion of epoxy coating. Furthermore, this type of pretreatment reduced the disruption of interfacial bonds at the binder/substrate interface. Addition of 2?wt% cerium nitrate into the silane formulation led to the maximum efficiency of resultant coating.     

纳米含氟磷灰石涂层及其在模拟溶液中的行为

以Ca(NO3)2×4H2O和P2O5乙醇溶液为先驱体，六氟磷酸(HPF6)为氟引入剂，采用溶胶-凝胶法在钛合金基板上制备含氟羟基磷灰石涂层. 获得的涂层晶粒尺寸为120~150 nm. 实验结果表明，加入HPF6后形成的含氟磷灰石涂层在模拟体液中有良好的生物活性特性，在柠檬酸改性的磷酸缓冲溶液中表现出较好的稳定性.