•MAO coated Ti has been heat treated in different atmospheres to improve bioactivity.•Flower-like rutile particles are formed on the MAO surface after heating in Ar at 800 °C.•The difference in O source is key factor for the formation of particles.•Attributing to the element diffusion, oxidized β-Ti prior grows along the discharge channel.Amorphous microarc oxidation (MAO) coating containing Ca, P, Si and Na elements on Ti substrate has been heat treated in different atmospheres (air or argon) to adjust the phase composition, surface structure and bioactivity. After heat treatment in air at 800 °C for 1 h, the coating consists of anatase, rutile and CaTi4(PO4)6, with almost unchanged microporous surface structure. As for the one treated in argon at 800 °C for 1 h, anatase and rutile are formed on the coating, and the coating surface is covered by flower-like rutile particles. The formation of rutile particles could be attributed to the prior growth of the oxidized β-Ti along the discharge channel caused by the diffusion of incorporated elements. Thanks to the crystallization of TiO2 and the rise of surface roughness, which provides good sites for apatite nucleation, the MAO coated Ti after heat treatment in argon at 800 °C exhibits good apatite-inducing ability.

Microarc oxidation (MAO) coating containing Ca, P, Si, and Na elements on a titanium (Ti) implant has been steam-hydrothermally treated and further mediated by post-heat treatment to overcome the compromised bone-implant integration. The bone regeneration, bone-implant contact, and biomechanical push-out force of the modified Ti implants are discussed thoroughly in this work. The best in vivo performances for the steam-hydrothermally treated one is attributed to the synergistic effects of surface chemistry and topologic structure. Through post-heat treatment, we can decouple the effects of surface chemistry and the nanoscale topologic structure easily. Attributed to the excellent in vivo performance of the surface-modified Ti implant, the steam-hydrothermal treatment could be a promising strategy to improve the osseointegration of the MAO coating covered Ti implant.Keywords: osseointegration; surface chemistry; surface modification; titanium; topologic structure;

H2Ti5O11·H2O nanorod arrays deposited on a titanium (Ti) surface have been fabricated via a hybrid technique of microarc oxidation (MAO) and chemical treatment. After the MAO treatment, an amorphous phase composed porous coating containing Ca, P, Si and Na elements was formed on the Ti surface. At the beginning of the chemical treatment, the elements of Ca, P, Si and Ti dissolved from the MAO coating into the solution. With a prolonged treatment time, nanorod arrays with a long aspect ratio were formed on the coating surface instead of the porous surface. The results revealed that the formed nanorods on the Ti surface were H2Ti5O11·H2O with the growth direction of [010]. This as-prepared Ti plate with a nanorod array surface exhibits a super-hydrophilic property, an excellent apatite-inducing ability and photocatalytic properties due to the existence of OH groups in the atomic structure of H2Ti5O11·H2O. The incorporated elements of Ca, P, Si and Na, and the corrosive attack of OH groups are the two factors for the formation of H2Ti5O11·H2O. The long and thin nature of the nanorods is attributed to the anisotropy of the atomic structure of H2Ti5O11·H2O with the lowest strain energy along the [010] direction based on the solid phase transformation.

A bioactive coating containing Ca, P, Si and Na elements with a porous surface structure has been fabricated on a titanium (Ti) plate by a three-step microarc oxidation. Randomly distributed gouges (80–200 μm) have been observed from the conformal MAO coating (with micro-scale pore size of 0.6–2 μm in morphology) covered Ti surface which exhibits double-level porous structure. Meanwhile, it is noticed that Ca, P, Si and Na elements have been incorporated into the MAO coating but show different oxidation states of elements between the flat surface and gouge surface. The XPS results reveal that Ti–OH and SiO2 gel have only formed on the gouge surface because of the decreased microarc oxidizing ability in the local area. Besides, the bioactivity of the different MAO step prepared Ti plates has been examined by simulated body fluid (SBF) immersion. As expected, the three-step MAO prepared Ti with double-level porous surface structure exhibits the best apatite-inducing ability thanks to the as-introduced Ti–OH and Si–OH groups.

•MAO coating covered Ti plates were steam-hydrothermally treated with NaOH solution.•HA and anatase were generated from the previously amorphous MAO coating.•The adding of NaOH can improve the densification of the formed coating.•Ti–OH is formed on the steam-hydrothermally treated MAO coating.•The coatings which are treated with NaOH solution show apatite-inducing ability.The microarc oxidation (MAO) coating covered pure Ti plates are steam-hydrothermally treated in autoclaves containing NaOH solutions with different concentrations of 0, 0.001, 0.01, 0.1 and 1 mol·L− 1. Due to the composition of Ti, O, Ca, P, Si and Na elements in the MAO coating, anatase and hydroxyapatite (HA) crystals are generated from the previously amorphous MAO coating after the steam-hydrothermal treatment. Meanwhile, it is noticed that the amount of HA crystals increases but showing a decline trend in aspect ratio in morphologies with the increasing of NaOH concentration. Interestingly, the steam-hydrothermally treated MAO coatings exhibit better bonding strength with Ti substrate (up to 43.8 ± 1.1 MPa) than that of the untreated one (20.1 ± 3.1 MPa). In addition, benefiting from the corrosive attack of the dissolved NaOH in water vapor on the MAO coating, Ti–OH is also formed on the steam-hydrothermally treated MAO coating surface, which can trigger apatite nucleation. Thus, the steam-hydrothermally treated MAO coatings exhibit good apatite-inducing ability.

Sphene–titanium oxide composite coatings are prepared by a hybrid technique of microarc oxidation (MAO) and heat treatment on titanium. The average roughness of the MAO coating increases after heat treatment due to the crystallization and crystal growth of the MAO coating. The wetting ability, roughness, phase composition and surface topological structure of the composite coatings have positive effects on the MC3T3-E1 cell attachment, proliferation and alkaline phosphatase activity. The composite coatings do not cause any hemolysis effect. Furthermore, they also do not give rise to any adverse reactions in vivo according to micro-CT images, radiographs and histological analysis. At the same time, the sphene–titanium oxide composite coatings show perfect osseointegration in rabbit tibia in vivo and display the higher interface bonding strength with rabbit tibia compared to the MAO coating without heat treatment, because the composite coatings have higher bioactivity, good cell response and mechanical properties, and so on.

Macroporous Ti with macropores of 50–400 μm size is prepared by sintering Ti microbeads with different diameters of 100, 200, 400, and 600 μm. Bioactive microarc oxidation (MAO) coatings with micropores of 2–5 μm size are prepared on the macroporous Ti. The MAO coatings are composed of a few TiO2 nanocrystals and lots of amorphous phases with Si, Ca, Ti, Na, and O elements. Compared to compact Ti, the MC3T3-E1 cell attachment is prolonged on macroporous Ti without and with MAO coatings; however, the cell proliferation number increases. These results are contributed to the effects of the space structure of macroporous Ti and the surface chemical feature and element dissolution of the MAO coatings during the cell culture. Macroporous Ti both without and with MAO coatings does not cause any adverse effects in vivo. The new bone grows well into the macropores and micropores of macroporous Ti with MAO coatings, showing good mechanical properties in vivo compared to Ti, MAO-treated Ti, and macroporous Ti because of its excellent osseointegration. Moreover, the MAO coatings not only show a high interface bonding strength with new bones but also connect well with macroporous Ti. Furthermore, the pushing out force for macroporous Ti with MAO coatings increases significantly with increasing microbead diameter.Keywords: macroporous Ti; MC3T3-E1 osteoblast; mechanical properties; microarc oxidation; osseointegration;

•Amorphous phase/TiO2 nanocrystal (APTN) composite coatings were fabricated.•The MC3T3-E1 cell response of the APTN coatings was evaluated.•The APTN coatings greatly enhanced the cell proliferation ability.Bioactive amorphous phase/TiO2 nanocrystal (APTN) composite coatings were fabricated by microarc oxidation (MAO) on Ti. The APTN coatings are composed of much amorphous phase with Si, Na, Ca, Ti and O elements and a few TiO2 nanocrystals. With increasing applied voltage, the micropore density of the APTN coating decreases and the micropore size of the APTN coating increases. The results indicate that less MC3T3-E1 cells attach on the APTN coatings as compared to Ti. However, the APTN coatings greatly enhance the cell proliferation ability and the activity of alkaline phosphatase. The amorphous phase and the concentrations of the released Ca and Si from the APTN coatings during cell culture have significant effects on the cell response.

The amorphous phase/TiO2 nanocrystals (APTN) composited coatings were prepared on Ti implants for biomedical applications. The Ti implants without and with the APTN composited coatings both do not cause any adverse effects after implantation into the rabbit tibia. The osseointegration of Ti implants after covering the APTN coatings is improved pronouncedly, greatly increasing the interface bonding strength between the implants and newly formed bones. In addition, it is interesting that the newly formed bone tissues appear in the micro-pores of the APTN coatings, promoting the interface bonding between the implants and new bones by the mechanical interlock. Moreover, the Ti implant with the APTN coatings formed at higher applied voltage exhibit higher shear strength and displacement during the pushing out experiment probably due to its better osseointegration.

•Mechanical properties of porous titanium with different diameters were studied.•Drug films were formed on microarc oxidized microbeads.•Release kinetic process of cefazolin sodium in composited films was investigated.Porous titanium was prepared by pressureless sintering of titanium beads with diameters of 100, 200, 400 and 600 μm. The results indicated that the mechanical properties of porous titanium changed significantly with different bead diameters. Plastic deformations such as necking phenomenon and dimple structure were observed on the fracture surface of porous titanium sintered by beads with diameter of 100 μm. However, it was difficult to find this phenomenon on the porous titanium with a titanium bead diameter of 600 μm. The microarc oxidized coatings were deposited on its surface to improve the bioactivity of porous titanium. Furthermore, the cefazolin sodium/chitosan composited films were fabricated on the microarc oxidized coatings for overcoming the inflammation due to implantation, showing good slow-release ability by addition of chitosan. And the release kinetic process of cefazolin sodium in composited films could be possibly fitted by a polynomial model.

Chemical treatment was used to modify the surface of microarc oxidized (MAO) coating containing Ca and P. And the chemically treated MAO (C-MAO) coating was further heat-treated at 400–800 °C. The average roughness of the MAO and C-MAO coatings is about 250 nm; further heat treatment improved the roughness of the C-MAO coating. The chemical and heat treatment enhanced the wetting ability of the MAO coating. During SBF immersion, amorphous Ca- and P-containing precipitate (Ca–P) appeared firstly, eventually transforming to crystalline apatites. At the same time, the apatite firstly formed at the concave region on the surface, and then spreads on the whole surface. The induced biomimetic apatite possessed a porous structure on two-scales of micron and nanometer levels. In the interlayer and outlayer of the C-MAO coating, the elements of Ca, P and Ti showed a gradient distribution. In the apatite layer, Ti disappeared basically, and the concentrations of Ca and P did not change obviously. In this work, continuous MG63 cell layer was observed on the surface of the C-MAO coating, which can provide good environment for the cell proliferation.

Alkaline electrolyte containing Si, Ca and Na elements was used to make porous coating of titanium dioxide on the titanium matrix surface by the way of micro-arc oxidation (MAO). The influences of MAO time on the microstructures and the distribution of elements in the coating surface was investigated. The results showed that the coating surface contains Ti, O, Si, Ca, Na. The contents of Si, Ca, and Na elements increase with the increasing of MAO time. After the MAO time reaches 10 minutes, the increasing speed of elements content decreases. The pore size of the coating surface is in direct proportion to the MAO time. The number of pores is in inverse proportion to the MAO time. After the MAO time reaches 5 minutes, the pore size increasing speed and the number of pores decreasing speed weaken.

Sphene–titanium oxide composite coatings are prepared by a hybrid technique of microarc oxidation (MAO) and heat treatment on titanium. The average roughness of the MAO coating increases after heat treatment due to the crystallization and crystal growth of the MAO coating. The wetting ability, roughness, phase composition and surface topological structure of the composite coatings have positive effects on the MC3T3-E1 cell attachment, proliferation and alkaline phosphatase activity. The composite coatings do not cause any hemolysis effect. Furthermore, they also do not give rise to any adverse reactions in vivo according to micro-CT images, radiographs and histological analysis. At the same time, the sphene–titanium oxide composite coatings show perfect osseointegration in rabbit tibia in vivo and display the higher interface bonding strength with rabbit tibia compared to the MAO coating without heat treatment, because the composite coatings have higher bioactivity, good cell response and mechanical properties, and so on.