Antibacterial and osteogenic activities of thiolated and aminated yttria-stabilized tetragonal zirconia polycrystal with tolerance to low temperature degradation

The chemical immobilization of silane on yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) surface is promising in improving both osseointegration and antibacterial activity, however, the effect of low temperature degradation (LTD)-induced the tetragonal (t) to monoclinic (m) phase transformation on the chemical bonding and continuous bioactivity remains unclear. In this study, 3-aminopropyltriethoxysilane (APTES) and 3-mercaptopropyltrimethoxysilane (MPTS) were grafted on the Y-TZP surface. Quantum chemistry revealed that Zr–O–Si bonds formed by t/m-ZrO2 both had a strong tendency to undergo hydrolysis in acidic or neutral environments, but were stable in alkaline environments. Inductively coupled plasma mass spectrometry showed that the release of Si increased during weeks 1–3 on both APTES- and MPTS-grafted surfaces, then decreased rapidly on MPTS-grafted surface while maintained a sustain release on APTES-grafted surface until week 4; in particular, the hydrolysis of Zr–O–Si bonds did not accelerated by LTD. X-ray photoelectron spectroscopy showed that LTD-induced reductions in Zr–O–Si bond contents on APTES- and MPTS-grafted surfaces were 0.63% and 1.79%, respectively. In vitro MC3T3-E1 cell experiments comfirmed that APTES- and MPTS-grafted Y-TZP surfaces maintained similar adhesion and proliferation before and after LTD. Scanning electron microscopy, laser confocal scanning microscopy, and spread plate assay findings showed favorable anti-Porphyromonas gingivalis (P. gingivalis) effects induced by APTES- and MPTS-grafted t/m-ZrO2 surfaces. Thus, APTES and MPTS both provide LTD-stable and hydrolysis-stable chemical bonding for Y-TZP implants, and t-m phase transformation does not cause detectable effects on Y-TZP bioactivity.