Characterization and cytocompatibility of hierarchical porous TiO2 coatings incorporated with calcium and strontium by one-step micro-arc oxidation

Abstract

Calcium (Ca) and strontium (Sr) are beneficial for bone reconstruction. This study incorporated Ca and Sr into the TiO₂ coatings by one-step micro-arc oxidation (MAO) treatment with CaO and SrO added in tetraborate electrolytes. The structure, composition, hydrophilicity, ion release, and cytocompatibility of the coatings were studied. The coatings combine layered micron-scale pores in various sizes and nano-scaled pores, forming a hierarchical structure. This hierarchical structure is highly porous and super-hydrophilic. The coatings are composed of Ti, O, and B, as well as Ca or Sr. Ca and Sr mainly distribute in the outer layer of the coatings and exist in the forms of carbonates and oxides. The formation of the coatings was discussed. Ca and Sr incorporated into the coatings are readily released into aqueous solutions. The homogeneous surface structure of the coatings leads to an excellent and approximating performance in hydrophilicity, as well as the adhesion and spreading of the human bone marrow-derived mesenchymal stem cells (hBMSCs). The simultaneous incorporation of Ca and Sr incorporation exhibits superior facilitation in the proliferation of hBMSCs compared with single Ca or Sr incorporation. This study shows a promising method to incorporate bioactive elements into the MAO coatings on titanium surfaces.

Keywords: Calcium; Cytocompatibility; Hierarchical structure; Micro-arc oxidation; Strontium; Super-hydrophilicity.