Osteoblast response to zirconia modified-ORMOSILs

In this study, an in vitro evaluation of the human osteoblasts response to Organically Modified Silicate (ORMOSIL) biomaterials was conducted. These materials were synthetized by sol-gel process being modified with zirconia (ZrO₂) and/or Ca²⁺. The materials were immersed into phosphate buffer solution (PBS) in order to test precipitation of mimetic apatite-like on their surfaces. ORMOSILs were characterized by SEM, FT-IR and X-RD analysis. The response of osteoblast to ORMOSILs was analyzed as a measure of cell adhesion, proliferation and differentiation. The results showed that the addition of Ca²⁺ ions modifies the surface morphology of ORMOSILs by forming precipitates of mimetic apatite-like with cauliflower and scales morphologies. On the other hand, biological results suggest that the incorporation of zirconia to ORMOSILs increases their ability to support cell adhesion and proliferation. However, the inclusion of both zirconia and Ca²⁺ in the ORMOSILs decreases their biological compatibility by showing less cell proliferation and lower osteonectin expression, a protein related to osteoblasts. The unfavorable effect of Ca²⁺ on cell proliferation and cell viability could be due to its ability to induce the formation of mimetic apatite-like with incompatible morphology. The analysis of other proteins related to bone formation on ORMOSIL-Zr and ORMOSIL-Zr-Ca surfaces demonstrated clear expression of osteopontin and osteocalcin in cells growth. In the case of ORMOSIL-Zr, the expression of osteonectin occurred at early stages while the expression of osteopontin and osteocalcin begun at later stages, indicating a switch from an early to a mature stage being stimulated by the biomaterial. Together, these results highlight the important role of zirconia and Ca²⁺ ions in the composition of materials regulating their biocompatibility when used as scaffolds in bone regeneration.