Osteogenesis regulation of mesenchymal stem cells via autophagy induced by silica–titanium composite surfaces with different mechanical moduli

The high surface elastic modulus of the titanium (Ti) implant is one of the critical factors causing poor osteointegration between the implant surface and surrounding bone tissue. To address this challenge, spherical silica nanoparticles (SSNs) and spherical titania nanoparticles (STNs) with different sizes were synthesized and embedded into Ti surfaces via a micro-arc oxidation (MAO) technique. There were no significant changes in the surface roughness and protein adsorption behaviors before and after the embedding of spherical silica nanoparticles and titania nanoparticles into the Ti implant. However, the surface elastic modulus of Ti-SSNs decreased from 93 GPa to 6.7 GPa, while there was still no change in surface elastic modulus between Ti and Ti-STN groups. In vitro experiments showed that Ti-SSNs, especially Ti-SSN3, significantly stimulated the expression level and nuclear localization of the transcription factor YAP. YAP/TAZ could further inhibit the phosphorylation of AKT and mTOR proteins in MSCs, leading to higher LC3-II protein expression and osteogenic differentiation of MSCs. Ti-SSNs also showed a higher level of autophagosome formation, ALP activity and mineralization capability compared to the other groups. Our results showed that the surface elasticity modulus of an implant plays an important role in the regulation of MSC behaviors. Therefore, designing an implant with an optimal elastic modulus at the surface might have great clinical potential in the bone repair field.