Improving osteogenic activity of Y-TZP (Yttria-stabilized tetragonal zirconia polycrystal) surfaces by grafting of silanes with different end groups

Highlights: • SH-terminal silanes performed superior chemical affinity with zirconia. • The organic end groups of silanes affected the characteristic of zirconia surface. • SH-, NH₂-terminal silanes promoted osteogenesis on Y-TZP surface. Poor osteogenesis caused by limited bioactivity is one of the challenges affecting the use of zirconia-based materials as implants. In this study, four representative silanes with different end groups [γ-methacryloxypropyltrimethoxysilane (γ-MPS, with a vinyl end group), methyltrimethoxysilane (MTMS, methyl end), 3-mercaptopropyltrimethoxysilane (MPTS, mercapto end), and 3-aminopropyltriethoxysilane (APTES, amino end)] were grafted on a Y-TZP surface with the purpose of improving its osteogenic activity. Thermodynamic and analytical chemistry results confirmed that the terminal alkoxy groups of the silanes could condense with the hydroxyl groups on the zirconia surface to form covalent Zr–O–Si bonds; in particular, mercapto- terminated silanes were more effective at combining with zirconia than hydrophobic vinyl- and methyl-terminated silanes. Y-TZP modified with mercapto- and amino-terminated silanes showed improved hydrophilicity, which in turn promoted cell adhesion and growth. In vitro cell experiments showed that mercapto- and amino-terminated silanes promoted osteogenic differentiation and mineralization by increasing osteocalcin (OCN) and osterix (OSX) expression levels, while vinyl- and methyl-terminal silanes exhibited inhibitory effects on the collagen type 1 (COL-1), Runt-related transcription factor 2 (Runx2), and OCN expressions. Therefore, grafting mercapto- and amino-terminal silanes is a simple and effective strategy for enhancing the osteogenic potential of Y-TZP implants.