Surface Modification Of Microarc Oxidized Ti And Its Cell Behaviors And Osteoinductive Property

Microarc oxidation （MAO） was used to produce TiO^2-based coatingscontaining Si and Ca on the surfaces of the entitative Ti and porous Ti prepared bysintering Ti beads. And then, the MAO coatings were modified by heat-treatmentand hydrothermal-treatment to enhance their bioactivity. The microstructures,mechanical properties, physical and chemical properties and apatite-formationability of the MAO coatings before and after modification were investigated by theX-ray diffraction（XRD）, raman spectroscopy（Raman）, scanning electronicmicroscope（SEM）, atomic force microscope（AFM）, X-ray photoelectronicspectroscopy（XPS）,fourier transform-Infrared spectra （FT-IR）,transmission electronmicroscope（TEM）, mechanics universal testing machines and nanoindentation. Theblood compatibility and cell biological behaviors such as cell proliferation, cellattachment, cytoskeleton and cellular activities of the MAO coatings without andwith modifications were investigated by microplate reader for ELISA, Laserscanning confocal microscope（CLMS） and ultraviolet-visible pectrophotometer. Thein vivo compatibility and bonding strength of the implants covered MAO coatingswithout and with subsequent modifications between new bones were investigatedafter implanting in rabbit tibia for different time by X-ray Diagnostic imaging,Micro-CT, Biomechanics, histologic cross-sectional anatomy. In addition, toovercome the inflammation resulted from implants, drug coating technique was usedto deposit antibacterial drugs on implants.In this paper, porous titanium was fabricated by sintering titanium beads withdifferent diameters of100,200,400and600μm. TiO^2-based coatings containing Siand Ca （SC） were prepared on entitative Ti and porous tianium in the electrolytecontaining EDTA-2Na, Ca(（CH₃COO）₂.H₂O, Na₂SiO₃.9H₂O and NaOH. The mainphase compositions of SC coatings are anatase and the main elemental compositionsare Ca, Si, Na, Ti and O. And the interface bonding strength between SC coatingsand Ti is good. With increasing the applied voltage, the concentrations of Ca, Si andNa increased and that of Ti decreased. A graded distribution in the elementalconcentration along the coating depth was observed. In the current results, thechemical states of Ti, O, Ca and Si were Ti⁴⁺and Ti²⁺, O^2-, Ca²⁺, Si⁴⁺. At the sametime, the applied voltage does not affect the chemical states of Ca and Si. In addition,the hardness, elastic modulus and corrosion resistance of SC coatings wereenhanced and the wetting ability and surface roughness of SC coatings improved byincrease the applied voltage. With increasing the titanium bead diameter, theporosity and mechanical properties decreased. In addition, the thickness of the SC coatings on the porous titanium increased.After heat treatment of the SC coating at700℃and800℃, rutile and sphenewere formed. With increasing heat treatment temperature, the surfaces of SCcoatings became rougher and the coating thickness, corrosion resistance andmechanical properties were improved. After heat treatment of SC coatings, except ofthe change in the chemical states of Ti²⁺to Ti⁴⁺, the chemical states of Ca, Si and Oelements did not change. On the surface of hydrothermal heated SC coatings,bamboo-, band-and line-like TiO₂were observed. During the hydrothermaltreatment process, Si and Ca elements were released into the NaOH aqueoussolution. In addition, TiO₂of SC coatings could be attacked by OH-ions in theNaOH aqueous solution, forming HTiO₃^-ions, which could result in the depositionof Ca²⁺and Na⁺ions on the modified surface to form calcium titanate and sodiumtitanate hydrates.During SBF immersion, the ionic exchange of Na⁺ions of SC coating with H₃O⁺ions in SBF can result in the formation of Si-OH groups, greatly promoting theapatite formation on the SC coatings. At the same time, the apatite can deposit in themicropores of SC coatings. In addition, increasing the applied voltage couldimprove the apatite forming ability of SC coatings due to high Ca and Siconcentrations in the SC coatings. The apatite forming ability of the porous titaniumis higher than that of entitative Ti due to its porous structure and higherconcentrations of Si and Ca. with increasing the heat treatment temperature, theapatite forming ability of SC coatings increased due to the formation of sphene. Thehydrothermal treated SC coatings show high apatite formation ability resulting fromthe formation of HA and titanates. During the SBF immersion process, the ionicexchanges of Ca²⁺and Na⁺ions of titanates on the hydrothermal treated SC coatingswith H₃O⁺ions in the SBF cause the formation of Ti-OH groups, which greatlyimprove the apatite formation ability. In addition, the induced apatites by all kindsof coatings contain HPO4^2-and CO3^2-groups.The cefazolin sodium/chitosan drug films on the SC coating show drugslow-release ability. The drug films could deposit into the micropores of SCcoatings. The increase of deposition times and the addition of chitosam can improvethe slow-release ability of drug film. And the slow-release ability of drug films onthe heat-treated SC coating at800oC is higher than that of other coatings. Thereactions between chitosam and cefazolin could involve coulombic interactions, vander Waals force, and H-bonding etc. In addition, interface reactions between drugfilms and SC and heat-treated SC coatings could occur such as physical andchemical absorption involving various groups such as Si-OH, Ti-O of substrates and-C=O,-OH and-NH2groups of drug films.The cell proliferation on the surface of SC coatings increased with increasing the applied voltage. The effect of SC coatings on the cellular activity is not obviouscompared to pure titanium. The cell attachment ability on the porous titanium withSC coatings was lower than that on pure titanium at the early cell culture. However,it enhanced at latter cell culture. Moreover, the morphology of the attached cells isrelative to the diameter of titanium beads. The porous titanium with SC coatings isbenefit to the cell proliferation at early cell culture after1and3days, however, noobvious difference in the cell proliferation was observed between porous titaniumwithout and with SC coatings after cell culture for7days. The effect of the titaniumbeads diameter on the cellular activity is not obvious. However, the porous structureof porous titanium could optimize the cell actin skeleton. With increasing the heattreatment temperature, the cell attachment, cell proliferation and cellular activitywere enhanced, at the same time, the cytoskeleton and cell morphology are good.Hydrothermal treatment could improve the cell proliferation and attachment on theSC coatings. In addition, the attaching morphology on the hydrothermal treated SCcoatings is integrity. The hydrothermal treatment procedure has not evident effect onthe cell attachment ratio, cell proliferation and cell activity. No All coatings showgood blood compatibility.The in vivo biocompatibility of the SC coatings before and after heat treatmentis very good, and no rejection and infection were found after implantation. Moreover,the bone tissue absorption is also good, and new bone could grow on the surface ofthe implants. The bone tissue and osteoblast could be observed on the surfaces of theimplants after being taken out from the rabbit tibia. The bonding strength betweennew bone and implants increased with increasing the applied voltage and heattreatment. The porous titanium with SC coatings shows similar in vivobiocompatibility compared to entitative Ti with SC coatings. However, the bondingstrength between implants and new bones is higher than that of entitative Ti, sincethe new bone can grow in the pores of the porous titanium. Good interfaces of newbones and various implants were observed after implanting for3months in rabbit.Above all, the entitative Ti with SC coatings before and after heat treatment orhydrothermal treatment, as well as the porous titanium with SC coatings, showsgood apatite forming ability, cell compatibility, blood compatibility and in vivobiocompatibility. In addition, The cefazolin sodium/chitosan drug films on the SCcoating show drug slow-release ability.