Bioactivity and cell proliferation in radiopaque gel-derived CaO-P2O5-SiO2-ZrO2 glass and glass-ceramic powders.

In this study, 10 mol% ZrO2 was added to a 27CaO-5P2O5-68SiO2 (mol%) base composition synthesized via a simple sol-gel method. This composition is similar to that of a frequently investigated bioactive gel-glass. The effects of ZrO2 on the in vitro bioactivity and MG-63 cell proliferation of the glass and its derivative polycrystalline (glass-ceramic) powder were investigated. The samples were characterized using thermo-gravimetric and differential thermal analysis (TG/DTA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) coupled to energy dispersive X-ray spectroscopy (EDS). Release of Si, Ca, P and Zr into simulated body fluid (SBF) was determined by inductively coupled plasma (ICP). Upon heat treatment at 1000 °C, the glass powder crystallized into an apatite-wollastonite-zirconia glass-ceramic powder. Hydroxycarbonate apatite (HCA) formation on the surface of the glass and glass-ceramic particles containing ZrO2 was confirmed by FTIR and SEM. Addition of ZrO2 to the base glass composition decreased the rate of HCA formation in vitro from one day to three days, and hence, ZrO2 could be employed to control the rate of apatite formation. However, the rate of HCA formation on the glass-ceramic powder containing ZrO2 crystal was equal to that in the base glassy powder. Tests with a cultured human osteoblast-like MG-63 cells revealed that the glass and glass-ceramic materials stimulated cell proliferation, indicating that they are biocompatible and are not cytotoxic in vitro. Moreover, zirconia clearly increased osteoblast proliferation over that of the Zr-free samples. This increase is likely associated with the lower solubility of these samples and, consequently, a smaller variation in the media pH. Despite the low solubility of these materials, bioactivity was maintained, indicating that these glassy and polycrystalline powders are potential candidates for bone graft substitutes and bone cements with the special feature of radiopacity.