Improved Corrosion Fatigue and Immunomodulatory Osteogenesis of Hydrothermally Grown TiO 2 Nanorods Coated SMATed-Titanium

Current active modifications of Ti-based materials for promoting osteogenesis often decrease corrosion fatigue strength (Lcf ) of the resultant implants, shortening their service lifespan. To solve the complication and accelerate osteogenesis, herein, a TiO2 nanorods (TNR)-arrayed coating was hydrothermally grown on optimally surface mechanical attrition treated (SMATed) titanium (S-Ti). The microstructure, bond integrity, residual stress distribution and corrosion fatigue of TNR coated S-Ti (TNR/S-Ti) as well as the response of macrophages and bone marrow-derived mesenchymal stem cells (BMSCs) to TNR/S-Ti were investigated, together with mechanically polished Ti (P-Ti), S-Ti and TNR coated P-Ti (TNR/P-Ti). Consequently, S-Ti displayed a nanograined layer and an underlying grains-deformed region both with residual compressive stress, which could be sustained even hydrothermally coated with TNR. TNR on S-Ti presented a nanotopography, composition and bond strength almost identical to that on P-Ti. While TNR/P-Ti displayed a considerable decrease in Lcf compared to P-Ti, TNR/S-Ti revealed an improved Lcf even higher than P-Ti. Biologically, TNR/S-Ti enhanced adhesion, differentiation and mineralization of BMSCs, but also promoted adhesion and M1-to-M2 transition of macrophages than S-Ti and P-Ti. With rapid phenotype switch of macrophages, pro-inflammatory cytokines decreased while anti-inflammatory cytokines upregulated. Under co-culture conditions, migration, differentiation and mineralization of BMSCs were enhanced by the increased secretion factors of macrophages on TNR/S-Ti. Such novel modification structure accelerated bone apposition in rabbit femur, and could be expected to elicit a favorable immune microenvironment to facilitate osseointegration earlier, but also simultaneously improve the corrosion fatigue resistance and thereby service-life of Ti-based implants.