Preparation And Biocompatibility Of Porous TiaO₂ Coatings Doped With Ca And Sr By Micro-arc Oxidation

Compared with other metallic materials,pure titanium has become a preferred material for human body tissue substitutes and restorations,such as dental implants,bone repair and artificial joints,because of its high specific strength,low elastic modulus,excellent biological corrosion resistance and biocompatibility.However,under natural conditions,a layer of biologically inert TiO₂ forms on the surface of pure titanium and its alloys,which reduces its surface biological activity.Therefore,such a biologically inert material requires to be surface-modified to increase its surface biological activity.At present,the"crater-like"TiO₂coating is one of the most common modified surfaces,still,its benefit to biological activity and hydrophilicity is insufficient,and the incorporation of Ca or Sr,two kinds of bioactive elements,is helpful to increase the biological activity.The TiO₂ coating with micro/nano dual structures shows high hydrophilicity and good biocompatibility.Therefore,this study aimed to incorporate Ca or Sr into a highly hydrophilic TiO₂ coating to further increase the biocompatibility.In this paper,strontium oxide（SrO）and calcium oxide（CaO）were added into the sodium tetraborate（Na₂B₄O₇）electrolyte,and the hierarchical structured TiO₂ coatings incorporated with Ca and Sr were prepared in a one-step MAO treatment.Studies have shown that a super-hydrophilic coating with micro/nano hierarchical structures can be prepared on the surface of pure titanium by MAO in the electrolyte of sodium tetraborate,and the formation of this unique structure is due to the dissolution of the oxides produced during the micro-plasma discharges by the tetraborate electrolyte.The addition of SrO and CaO into the electrolyte of Na₂B₄O₇ alters the dissolution of the oxides,resulting in the formation of submicron and micron-scale pores on the surface of the TiO₂ coating.This hierarchical structure endues the TiO₂ coating a high hydrophilicity.The Ca or Sr element was successfully incorporated into the TiO₂ coating.Through the cellular adhesion and spreading tests,this porous TiO₂ coating with hierarchical structure is verified beneficial to the cellular adhesion.However,it has little effect on the cellular spreading.By diluting the extracts of the coatings,in which cellular proliferation was examined,a proper concentration of Ca²⁺or Sr²⁺was suggested to promote the proliferation of the cells.The results show that Ca and Sr was successfully incorporated into the TiO₂ coatings with hierarchical pores by the MAO treatment with the addition of SrO and CaO into the electrolyte of Na₂B₄O₇.These coatings present excellent hydrophilicity and good biocompatibility.