Micro-arc Oxidation Surface Research Articles

Preparation and Biological Activity of Strontium Modified Titanium Oxide Surface

Titanium (Ti) is a bone tissue replacement material with excellent mechanical properties. However, Ti has poor biological activity and lacks osseointegrative properties and may trigger inflammation and cause implantation failure. To address these issues, Ti surface modification has become a widely used method. In this study, using microarc oxidation (MAO) technology, a strontium-doped MAO coating was prepared on Ti surfaces in an electrolyte solution comprising calcium acetate, calcium glycerophosphate and strontium acetate. Scanning electron microscopy (SEM) and energy spectrum analysis (EDS) were used to analyze the tissue structure and elemental composition of the coating. The surface phase composition of the coating was analyzed by X-ray diffraction (XRD). We observed the proliferation of cells on the coating surface through in vitro cell experiments. The results showed the surface of the strontium-doped MAO coating is porous, and strontium is evenly distributed on the surface. The coating can promote the adhesion, proliferation and differentiation of osteoblasts and has good biological activity and thus, could potentially be applied to the surface of implants in clinical application.

Layer-by-layer self-assembled polyurea layers onto MAO surface for enhancing corrosion protection to aluminum alloy 6063

Structural defects such as micro-pores and cracks generated during the micro-arc oxidation process can greatly reduce the corrosion resistance of the coating. This work proposed a method to improve the anti-corrosion property of the micro-arc oxidation (MAO) coating by layer-by-layer (LBL) assembling a polyurea layer on the surface of it. Organic silane (KH) and isophorone diisocyanate (IPDI) were self-assembled alternately on the MAO coating surface and formed a polyurea layer. The assembled layers were investigated using XPS, FTIR, EDS-SEM, EIS and polarization curves measurements. Three organic layers obtained couldn't be seen from SEM morphology. Whereas the XPS results showed the existence of polyurea layers with the disappearance of Al 2p signals and appearance of N 1s signals. The MAO coating surface was hydrophilic, and the contact angles of samples with odd-numbered layer (KH550 surface) were up to 95°, while the samples with even-numbered layer (IPDI surface) were about 87°, meaning that the silane and IPDI were successfully assembled on the MAO surface, improving the hydrophobicity of coating. The KH550/IPDI coating exhibited remarkably corrosion protection, and the corrosion resistance of the coating was maintained above 109 Ω·cm2 after exposure in NaCl solution for 288 h. In addition, the self-corrosion current density was under 1.46 × 10−9 mA·cm−2 after 288 h immersion, indicating that the KH550/IPDI coating would keep the anti-corrosion ability for longer time.

Effect of Micro-arc Oxidation Time on Corrosion Resistance of Magnesium Alloys

This experiment investigates the effect of time on the quality of the film during the micro-arc oxidation of magnesium alloys. The micro-arc oxidation surface morphology, the thickness of the film layer, and the influence on the corrosion resistance of the magnesium alloy were studied at different times. The experiment found that when the micro-arc oxidation time is controlled at 9 minutes, the surface quality of the film layer is the best, and the improvement of the corrosion resistance is more obvious.

Experimental Study on Friction Characteristics of Micro-Arc Oxidation Modified Layer on Titanium Alloy Surface

In order to study the effect of microarc oxidation modification treatment on the friction properties of titanium alloy surface, the surface treatment layer of Ti-6Al-4V ELI specimen modified by Microarc oxidation surface was sampled, the surface layer hardness, roughness and treatment layer thickness were tested, the microscopic morphology was analyzed, The friction tests of TC4 substrate and micro-arc oxidation treatment surface disc with 25% glass fiber, 15% fiberglass +5% graphite and 60% tin bronze reinforced PTFE pin were carried out, and the results showed that the thickness increased slightly and the surface layer hardness increased by about 75% after the micro-arc oxidation surface modification treatment. Compared with the substrate, the surface roughness is obviously improved, and the friction coefficient of the surface treatment specimen is similar to that of the TC4 titanium alloy substrate, but the wear amount is higher than that of the TC4 titanium alloy substrate.

Microarc oxidation surface of titanium implants promote osteogenic differentiation by activating ERK1/2-miR-1827-Osterix.

There has been a constant requirement from the clinic to develop biomedical titanium (Ti) implants with high osteogenic ability. In this study, we clarified a novel mechanism of how MAO (microarc oxidation) coating of Ti implants facilitates osteogenic differentiation of human bone marrow mesenchymal stem cells (hB-MSCs) by activating ERK1/2-miR-1827-Osterix signaling pathway in vitro. MAO surface of titanium implant was more favorable to promote osteogenic differentiation than SLA and AOS coating. Besides, titanium implants regulated hB-MSCs osteogenesis through the p38 MAPK pathway and ERK1/2 might be the most efficient target. Furthermore, MAO coating induced osteogenic differentiation though ERK1/2-miR-1827 pathway. Finally, we verified miR-1827 regulated osteogenic differentiation partially through Osterix. Our study reveals novel insights that MAO surface of titanium implant is a prior choice for biomedical trial and for its use in periprosthetic osteolysis (PIO) treatment in an evidence-based rationale.

In vitro degradation and cytocompatibility of a low temperature in-situ grown self-healing Mg-Al LDH coating on MAO-coated magnesium alloy AZ31

Basically, Mg–Al layered double hydroxide (LDH) coatings are prepared on the surface of micro-arc oxidation (MAO) coated magnesium (Mg) alloys at a high temperature or a low pH value. This scenario leads to the growth rate of LDH coating inferior to the dissolution rate of the MAO coating. This in turn results in limited corrosion resistance of the composite coating. In this study, a Mg–Al LDH coating on MAO-coated Mg alloy AZ31 is prepared through a water bath with a higher pH (13.76) at a lower temperature (60 °C). FE-SEM, EDS, XRD, XPS, and FT-IR are applied to analyze the surface morphology, chemical compositions, and growth process. Electrochemical polarization, electrochemical impedance spectroscopy (EIS) and hydrogen evolution tests are employed to evaluate the corrosion resistance of the samples. The results disclose that the MAO coating is completely covered by the nanosheet-structured LDH coating with a thickness of approximately 3.8 μm. The corrosion current density of the MAO-LDH composite coating is decreased four orders of magnitude in comparison to its substrate; the presence of a wide passivation region in anodic polarization branch demonstrates its strong self-healing ability, indicating the hybrid coating possesses excellent corrosion resistance. The formation mechanism of the LDH coating on the MAO-coated Mg alloy is proposed. Furthermore, the cytocompatibility is assessed via an indirect extraction test for MC3T3-E1 pre-osteoblasts, which indicates an acceptable cytocompatibility of osteoblasts for the composite coating.

Biodegradable Magnesium Bone Implants Coated with a Novel Bioceramic Nanocomposite.

Magnesium (Mg) alloys are being investigated as a biodegradable metallic biomaterial because of their mechanical property profile, which is similar to the human bone. However, implants based on Mg alloys are corroded quickly in the body before the bone fracture is fully healed. Therefore, we aimed to reduce the corrosion rate of Mg using a double protective layer. We used a magnesium-aluminum-zinc alloy (AZ91) and treated its surface with micro-arc oxidation (MAO) technique to first form an intermediate layer. Next, a bioceramic nanocomposite composed of diopside, bredigite, and fluoridated hydroxyapatite (FHA) was coated on the surface of MAO treated AZ91 using the electrophoretic deposition (EPD) technique. Our in vivo results showed a significant enhancement in the bioactivity of the nanocomposite coated AZ91 implant compared to the uncoated control implant. Implantation of the uncoated AZ91 caused a significant release of hydrogen bubbles around the implant, which was reduced when the nanocomposite coated implants were used. Using histology, this reduction in the corrosion rate of the coated implants resulted in an improved new bone formation and reduced inflammation in the interface of the implants and the surrounding tissue. Hence, our strategy using a MAO/EPD of a bioceramic nanocomposite coating (i.e., diopside-bredigite-FHA) can significantly reduce the corrosion rate and improve the bioactivity of the biodegradable AZ91 Mg implant.

Design and in situ prepare a novel composite coating on Mg alloy for active anti-corrosion protection

In this paper, a novel composite coating combining Layered Double Hydroxides (LDH) film and Micro-arc Oxidation (MAO) ceramic layer was designed to further enhance anti-corrosion protection of coating. The MgFe-LDH/MAO composite coating was prepared through in situ synthesis MgFe-LDH nanoflakes on the surface of MAO coating. Subsequently, the active anti-corrosion mechanism of MgFe-LDH layer was revealed through microstructure characterization and electrochemical test. Furthermore, the interaction between LDH nanoflakes and original MAO coating was investigated, too. The results show that: LDH nanoflakes preferentially grow in the pores of original MAO coating, and form a dense layer on MAO coating. In situ prepared LDH layer gives a strong and stable adhesion on MAO coating, besides the dissolution of original MAO coating affects LDH growth. MgFe-LDH layer supplied an active anti-corrosion protection for Mg alloy, since LDH can effectively seal the inherent defects of MAO coating and absorb corrosive medium in environment. • A novel LDH/MAO composite coating was prepared through in situ synthesis. • Reveal the interaction between LDH layer and original MAO coating. • 3.LDH/MAO composite coating exhibits excellent anti-corrosion protection for Mg alloy. • 4.Reveal the anticorrosive protection mechanism of LDH layer.

An anti-stripping and self-healing micro-arc oxidation/acrylamide gel composite coating on magnesium alloy AZ31

Biomaterial polyacrylamide (PAM) hydrogel was first studied for self-healing coatings of Mg alloys. In this work, a PAM gel with Ce4+ inhibitor was in-situ composited on the surface of micro-arc oxidation treated AZ31 Mg alloy. The results indicated that the scratched samples with the composite coating could avoid pitting corrosions and self-heal in neutral salt spray test (NSST). XPS and SEM-EDS analysis reveal that the self-healing performance was ascribable to the inhibition of Ce4+ and the bridge adsorption of PAM gels. Moreover, the results of open circuit potential and polarization curve indicate that the self-healing product film has good corrosion resistance.

Chemical and Biological Roles of Zinc in a Porous Titanium Dioxide Layer Formed by Micro-Arc Oxidation

This study investigated the time transient effect of zinc (Zn) in the porous titanium dioxide formed by micro-arc oxidation (MAO) treatment routinely performed for Zn-containing electrolytes. The aim of our analysis was to understand the changes in both the chemical and biological properties of Zn in physiological saline. The morphology of the Zn-incorporated MAO surface did not change, and a small amount of Zn ions were released at early stages of incubation in saline. We observed a decrease in Zn concentration in the oxide layer because its release and chemical state (Zn2+ compound to ZnO) changed over time during incubation in saline. In addition, the antibacterial property of the Zn-incorporated MAO surface developed at late periods after the incubation process over a course of 28 days. Furthermore, osteogenic cells were able to proliferate and were calcified on the specimens with Zn. The changes related to Zn in saline had non-toxic effects on the osteogenic cells. In conclusion, the time transient effect of Zn in a porous titanium dioxide layer was beneficial to realize dual functions, namely the antibacterial property and osteogenic cell compatibility. Our study suggests the importance of the chemical state changes of Zn to control its chemical and biological properties.

Surface and in vitro properties of Ag-deposited antibacterial and bioactive coatings on AZ31 Mg alloy

Ag (silver)-based bioceramic coatings were fabricated on AZ31 Mg alloy by combining the MAO (micro-arc oxidation) and PVD (physical vapor deposition) methods. As a first step, AZ31 Mg surfaces were coated using MAO using a solution consisting of sodium silicate and potassium hydroxide. As a second step, an Ag layer was accumulated on the MAO surfaces using the PVD method. The XRD patterns thus obtained demonstrated the presences of Mg (magnesium), Si (silicon), M2SiO4 (forsterite) and MgO (periclase) on the Ag-deposited MAO surfaces. The elemental or compound structures of Ag were not detected due to the homogeneous distribution of a trace amount of Ag on the surfaces. Both coatings' surfaces were porous due to the existence of discharge channels. All elements were found to be uniformly distributed across the entirety of the surfaces. The Ag-deposited MAO surfaces were found to have hydrophobic properties with respect to plain MAO surfaces. Newly formed layers consisted of Ca15(SiO4)6(PO4)2 (calcium silicate phosphate), Ca3(PO4)2 (tuite) and Ca10(PO4)6(OH)2 (hydroxyapatite) as produced on plain MAO and Ag-deposited MAO surfaces by immersion in SBF (simulated body fluid); these layers were more homogeneous on Ag-deposited MAO coatings than ones on plain MAO. Also, for E. coli (Escherichia coli) and S. aureus (Staphylococcus aureus) bacteria, the numbers of active bacterial colonies on Ag-deposited MAO surfaces were significantly reduced with respect to plain MAO surfaces.

Enhancing osseointegration of titanium implants through large-grit sandblasting combined with micro-arc oxidation surface modification.

The demand for titanium dental implants has risen sharply. However, the clinical success rate of implant surgery needs to be improved. In this paper, we report a novel surface modification strategy, large-grit sandblasting combined with micro-arc oxidation (SL-MAO), aiming to promote peri-implant bone formation and osseointegration of titanium implants. Modified titanium samples were prepared by large-grit sandblasting and acid etching (SLA), micro-arc oxidation (MAO), and SL-MAO. The resulting topographical changes and chemical composition of the samples were examined by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), respectively, and the biocompatibility and bioactivity were analyzed by bone-marrow mesenchymal stem cells (BMMSC) adhesion tests. Modified titanium implants were also inserted into the femurs of beagle dogs, and their competence of osseointegration was appraised by quantitative histomorphometry and micro-computed-tomography (micro-CT) analyses. Compared to SLA and MAO techniques, SL-MAO surface modification further enhanced titanium surfaces by creating a topographic morphology characterized by both micron-sized craters and sub-micron-scale pits, and resulted in superior chemical composition, which promoted cell adhesion, proliferation, and osteogenic differentiation. SL-MAO-modified titanium implants osseointegrated more efficiently than SLA or MAO controls, with significantly higher bone-area (BA) ratio and bone-implant contact (BIC) in the peri-implant region. The SL-MAO surface modification technique optimized the surface properties of titanium implants and enhanced peri-implant bone formation and osseointegration.

Characterization, Bioactivity and Antibacterial Properties of Copper-Based TiO2 Bioceramic Coatings Fabricated on Titanium

The bioactive and anti-bacterial Cu-based bioceramic TiO2 coatings have been fabricated on cp-Ti (Grade 2) by two-steps. These two-steps combine micro-arc oxidation (MAO) and physical vapor deposition–thermal evaporation (PVD-TE) techniques for dental implant applications. As a first step, all surfaces of cp-Ti substrate were coated by MAO technique in an alkaline electrolyte, consisting of Na3PO4 and KOH in de-ionized water. Then, as a second step, a copper (Cu) nano-layer with 5 nm thickness was deposited on the MAO by PVD-TE technique. Phase structure, morphology, elemental amounts, thickness, roughness and wettability of the MAO and Cu-based MAO coating surfaces were characterized by XRD (powder- and TF-XRD), SEM, EDS, eddy current device, surface profilometer and contact angle goniometer, respectively. The powder- and TF-XRD spectral analyses showed that Ti, TiO2, anatase-TiO2 and rutile-TiO2 existed on the MAO and Cu-based MAO coatings’ surfaces. All coatings’ surfaces were porous and rough, owing to the presence of micro sparks through MAO. Furthermore, the surface morphology of Cu-based MAO was not changed. Also, the Cu-based MAO coating has more hydrophilic properties than the MAO coating. In vitro bioactivity and in vitro antibacterial properties of the coatings have been investigated by immersion in simulated body fluid (SBF) at 36.5 °C for 28 days and bacterial adhesion for gram-positive (S. aureus) and gram-negative (E. coli) bacteria, respectively. The apatite layer was formed on the MAO and Cu-based MAO surfaces at post-immersion in SBF and therefore, the bioactivity of Cu-based MAO surface was increased to the MAO surface. Also, for S. aureus and E. coli, the antibacterial properties of Cu-based MAO coatings were significantly improved compared to one of the uncoated MAO surfaces. These results suggested that Cu-based MAO coatings on cp-Ti could be a promising candidate for biomedical dental implant applications.

Effect of micro-groove on microstructure and performance of MAO ceramic coating fabricated on the surface of aluminum alloy

Micro-arc oxidation (MAO) ceramic coatings on the surface of aluminum alloy substrates with and without micro-groove have been successfully fabricated in the Na2SiO3-NaOH-EDTA-2Na solution. Microstructure characterization indicated that the micro-grooves on substrate surface could increase the content of α-Al2O3, γ-Al2O3 and 3Al2O3·2SiO2 phases and reduce the content of Al phase in the ceramic coating due to the sharp corner effect. EDS and XPS analysis showed that the content of Al and Si on the near outer surface of MAO coating on grooved substrate was more than that on non-grooved substrate. Meanwhile, MAO ceramic coating on micro-grooved substrate exhibited the faster growth rate in the initial stage of oxidation and the lower growth rate in the later oxidation. The final MAO coating showed the bigger micro pores and thicker oxidation film compared with that on the non-grooved substrate. Furthermore, the surface micro grooving pretreatment could dramatically improve the wear resistance and hardness of MAO coating, and the highest hardness of ceramic coatings of grooved substrate was around 1715 HV, which could be attributed to their special trapezoidal micro-groove structure.

Rapid nano-scale surface modification on micro-arc oxidation coated titanium by microwave-assisted hydrothermal process

Nano to submicron scaled surface possesses excellent biological affinity and several processes have been undertaken to develop titanium implant with specific surface chemical and phase composition and nano-scale features. A simple process was used to modify the nano topographies on a micro-arc-oxidation (MAO) surface which shortens the time for the conventional hydrothermal process (HT). Nano-scaled anatase precipitates on the MAO surface with different crystallinities and morphologies were regulated via microwave-assisted hydrothermal in pure water (MWDD) or in pH conditioned mediums containing calcium and phosphorus ions (MWCP, MWCP9, MWCP11). The surface morphologies and structures were investigated by SEM, XRD, FTIR, and TEM. Anatase crystals as nano-spikes along [001] direction were observed on the surface of the MWDD and MWCP groups. Increasing the pH of the conditioned medium leads the precipitate to lose its crystallinity; the surface of MWCP11 is covered with amorphous anatase which has a 3D nano-sheet architecture. The MW treated surfaces possess superior hydrophilicity can adsorb more proteins (fibronectin and bovine serum albumin), and the osteoblasts-like MG63 cells on these surfaces have higher spreading ratios than on the MAO and HT groups. The cell viabilities in the MW groups were significantly higher than in the MAO and HT groups on the 7th day (P < 0.05), although their cell viabilities were similar on the first day. MWCP and MWCP11 have higher alkaline phosphatase activity on days 7 and 14 compared to other groups (P < 0.05). The MW treatment produces different nanomorphologies on the MAO surface and retains the original micro/submicron pores and surface calcium and phosphorus contents, thus it is expected to promote osseointegration without compromising the bond strength.

The development of Cu-incorporated micro/nano-topographical bio-ceramic coatings for enhanced osteoblast response

In order to take advantages of the structural complexity of hierarchical topography and benefits of Cu, novel Cu-incorporated micro/nano-topographical coatings were developed on titanium (Ti) substrates using micro-arc oxidation (MAO) and hydrothermal treatment. A post heat treatment was employed to alter the morphology of the nanostructures and modulate the release of Cu2+. The structural evolution, phase composition, surface wettability, ion release and protein adsorption of the coatings were investigated. The results showed that the MAO-fabricated coating (denoted as MAO surface) was composed of porous TiO2 matrix distributed with CaO, SiO2 and CaSiO3 amorphous compounds. After hydrothermal treatment, a thin layer of nano-particles (20 nm in diameter) composed of CuO and calcium silicate hydrate formed on MAO surface (denoted as MAO-HT surface). These nano-particles grew to larger ones (65 nm in diameter) composed of crystallized CaO·3CuO·4TiO2 and CaO·TiO2·SiO2 after post heat treatment (denoted as MAO-HT2 surface). Moreover, the ion release rate and surface hydrophilicity of various coatings followed the trend: MAO surface > MAO-HT surface > MAO-HT2 surface. The amounts of adsorbed proteins were comparable on all surfaces. Furthermore, SaOS-2 cell response to various surfaces was investigated. The results showed that the viability of cells was significantly inhibited on MAO-HT surface due to the cyto-toxicity of high concentration Cu2+ release. However, the attachment, proliferation and differentiation of SaOS-2 cells were enhanced on MAO-HT2 surface compared to MAO surface. The results indicate that modifying Ti surface with hierarchical micro/nano-topography could lead to enhanced osteoblast response.

Fabrication, characterization and in vitro properties of silver-incorporated TiO2 coatings on titanium by thermal evaporation and micro-arc oxidation

In this study, as a first step, a silver (Ag) thin film layer was deposited on cp-Ti (Grade-2) by thermal evaporation-physical vapor deposition (TE-PVD). And then, Ag-based titanium surface was coated by micro-arc oxidation (MAO) in solution, consisting of sodium silicate and potassium hydroxide at the second step. The phase structure, surface morphology, elemental composition, functional groups, wettability and surface topography of both coatings were characterized by XRD, SEM, EDS-mapping, contact angle goniometer, ATR-FTIR and surface profilometer, respectively. The XRD results indicated that anatase and rutile were detected on the surface after MAO and TE + MAO. Both coatings' surfaces were rough and porous due to the existence of plasma chemical reactions on micro discharge channels. The Ag-incorporated MAO coating exhibited much more hydrophilic character than MAO coating. The Ag was homogeneously distributed through the surface. The biological properties such as bioactivity and anti-bacterial tests of the coatings were analyzed by immersion test in SBF and bacterial formation. The apatite-forming abilities of both coatings were evaluated by soaking in simulated body fluid (SBF) up to 28 days. After soaking, apatite structure was formed on the MAO and Ag-incorporated MAO surfaces and the bioactivity of MAO surface on Ti was considerably improved compared to the MAO surface under SBF conditions. The homogenous and dense apatite distribution was observed on Ag-incorporated MAO coatings. The bacterial adhesion of Ag-incorporated MAO coatings was significantly reduced compared to plain MAO surface.

Reduced inflammatory response by incorporating magnesium into porous TiO2 coating on titanium substrate.

The implant materials with proper anti-inflammatory and osteogenic properties may be promising for orthopedic applications. The inflammatory response induced by biomaterials has been regarded as one of the critical factors in determining in vivo fate of implants. Therefore, a novel bone biomaterial should have inflammation regulatory effects instead of being completely bio-inert. In the present work, the inflammation regulatory effects of exogenous magnesium (Mg) ions were investigated. Under the stimulation of lipopolysaccharide (LPS), macrophages exposed to Mg2+ exhibited down-regulated gene expressions of M1 markers (CD86, CD11c and inducible nitric oxide synthase (iNOS)) and pro-inflammatory cytokines (tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) and IL-1β), up-regulated gene expression of M2 marker CD163 and decreased TNF-α release, indicating that Mg2+ could switch macrophages from M1 to M2 phenotype. Thereafter, micro-arc oxidation (MAO) technique was employed to fabricate Mg-containing ceramic coatings on titanium substrates. Macrophages grown on Mg-containing surface were switched from M1 to M2 phenotype with the stimulation of LPS, evidenced by suppressed gene expressions of M1 markers (CD86, CD11c and iNOS) and pro-inflammatory cytokines (TNF-α and IL-1β), promoted gene expression of M2 marker CD163 and decreased TNF-α release. Moreover, gene expressions of bone morphogenetic protein-2 (BMP-2), BMP-6 and vascular endothelial growth factor (VEGF) were up-regulated on Mg incorporated MAO surface without LPS stimulation. Together, Mg could be used as an anti-inflammatory agent for suppressing inflammation and mediating osteogenesis. The integration of Mg in biomaterials could endow bone biomaterials with anti-inflammatory property.

The Cu-containing TiO2 coatings with modulatory effects on macrophage polarization and bactericidal capacity prepared by micro-arc oxidation on titanium substrates.

The implant materials with both osteogenic and anti-bacterial properties are promising for orthopedic and dental applications. Moreover, the inflammatory response induced by biomaterials has been recently recognized as one of the critical factors in determining implantation fate. A new generation of implant materials should have modulatory effects on the local inflammatory environment such that it favors osteogenesis and osteointegration instead of being bio-inert. In this study, the micro-arc oxidation (MAO) technique was employed to fabricate Cu-containing ceramic coatings on titanium substrates. The macrophages cultured on Cu-containing MAO-fabricated surfaces were polarized to M1 phenotype, evidenced by the high expression levels of inducible nitric oxide synthase (iNOS), low expression levels of arginase1 (Arg1), enhanced pro-inflammatory cytokine interleukin-6 (IL-6) release and inhibited IL-4 and IL-10 (anti-inflammatory cytokines) release. The MAO-treated surface incorporated with larger amounts of Cu (referred as Cu(h)-MAO) could modulate a favorable inflammatory microenvironment for osteoblast-like cell differentiation. Moreover, the macrophages cultured on Cu(h)-MAO surface exhibited enhanced bacteria uptake and killing rate, indicating that the Cu(h)-MAO surface promoted the bactericidal capacity of macrophages. Together, Cu could be used as a promising modulatory agent for macrophage functions. The integration of Cu in biomaterials could lead to enhanced macrophage-mediated osteogenesis and bactericidal capacity.

High temperature tribological behavior of microarc oxidation film on Ti-39Nb-6Zr alloy

The TiO2-Nb2O5-ZrO2 composite film on Ti-39Nb-6Zr alloy was in-situ synthesized by microarc oxidation (MAO) process in potassium hydroxide electrolyte. Morphology, composition and hardness of MAO film were characterized. The tribological behavior of bare and coated Ti-39Nb-6Zr alloy under dry sliding against ZrO2 ceramic ball were studied by a ball-on-disk friction tester at the ambient temperature, 200 °C and 400 °C. Their friction coefficient and wear rate were obtained and wear mechanism analyzed. The MAO surface treatment significantly decreased friction coefficient and wear rate of Ti-39Nb-6Zr alloy at the ambient temperature and 200 °C, but the friction coefficient showed a periodical fluctuation at 400 °C while the wear rate clearly decreased. The MAO film has excellent wear resistance at different temperatures due to the formation of TiO2, Nb2O5, and ZrO2 ceramic phases. The wear mechanism of Ti-39Nb-6Zr alloy was mainly the abrasive wear at ambient temperature, but was transformed to abrasive, adhesive and oxidation wear at high temperature. The MAO treated alloy mainly displayed the adhesive wear at ambient temperature, 200 °C and 400 °C. Furthermore, the polished treatment for MAO film could obviously reduce its low friction coefficient and wear rate at the ambient temperature and 200 °C.