Formation mechanism and cytocompatibility of nano-shaped calcium silicate hydrate/calcium titanium silicate/TiO2 composite coatings on titanium

Abstract

Bilayered (HT0.5h and HT1h) and triple-layered (HT2h, HT6h and HT24h) coatings were fabricated on Ti using a hybrid process of microarc oxidation (MAO) and hydrothermal treatment (HT). The bilayered coatings comprise an outer layer of nanofloc Ca(Si_1.9Ti_0.1)O₅ and an inner layer of microporous TiO₂. The triple-layered coatings comprise an outer layer of nanoleaf or nanoribbon Ca₃Si₆O₁₅(H₂O)₇, a middle layer of nanograined Ca(Si_1.9Ti_0.1)O₅ and an inner layer of microporous TiO₂. The hydrothermal formation mechanism of the coatings was explored. The adhesion strength, hydrophilicity and cytocompatibility of selected coatings were investigated. During HT, Ca²⁺ incorporated into the TiO₂ layer migrates out and reacts with SiO₃²⁻ as well as HTiO₃⁻, resulting in the formation of Ca(Si_1.9Ti_0.1)O₅. Ca₃Si₆O₁₅(H₂O)₇ nanoleaves nucleate from Ca(Si_1.9Ti_0.1)O₅ preformed on the TiO₂ and grow in length and width to nanoribbons at the expense of Ca²⁺ and SiO₃²⁻ ions. The nanofloc (HT0.5h and HT1h), nanoleaf (HT2h) and nanoribbon (HT6h) coated surfaces display firm adhesion to substrates and super hydrophilicity. Compared with as-MAOed TiO₂, HTed coatings including HT0.5h, HT1h and HT2h enhance the mitochondrial activity, adhesion and proliferation of osteoblasts, and HT2h appears far more effective in accelerating the differentiation of osteoblasts.