SiO₂−P₂O₅−CaO Glasses and Glass-Ceramics with and without ZnO: Relationships among Composition, Microstructure, and Bioactivity

Abstract

Bioactive glasses and glass-ceramics of the system SiO 2 -P 2 O 5 -CaO with and without zinc were synthesized by sol-gel with the aim to address the influence of both the chemical composition and the microstructure on the growth of hydroxycarbonate apatite (HCA) following soaking in simulated body fluid (SBF). In the standard compositions 58S, 70S, and 80S the silica precursor was also partially replaced with a nanoscale silica powder (HiSil) in order to separate the contributions of porosity and composition. The combined use of XRPD, N 2 absorption measurements, and SEM allowed us to establish quantitative correlations among the above-mentioned quantities. We found that the HCA formation rate increases with the silica content and that an important role is played by the specific surface area of the samples. Notably, the addition of even small quantities (0.4 wt %) of ZnO at the expenses of both CaO and P 2 O 5 in the 58S glass leads to the increase, with respect to the 58S sample, of both the HCA formation rate and the HCA content after 8 days of treatment in SBF. A preliminary result revealed that sample with 0.4 wt % ZnO displayed good in vitro biocompatibility as shown by LDH assay.

In vitro calcified matrix deposition by human osteoblasts onto a zinc-containing bioactive glass

“…In detail, the presence of zinc clearly increased the HCA formation rate upon immersion in SBF; this increase was proportional to the zinc content (see Fig. 1, redrawn from Bini et al (2009). As expected, silica did not show any bioactivity.…”

“…In a previous study we reported preliminary evidence that a good balance between activity and toxicity, at least in vitro, can be obtained by means of carefully controlling the zinc content (Bini et al, 2009). In detail, the presence of zinc clearly increased the HCA formation rate upon immersion in SBF; this increase was proportional to the zinc content (see Fig.…”

“…In contrast, Balamurugan et al reported a minimal cytotoxicity with sol-gel glass composition of (mol%) 64% SiO 2 , 26% CaO, 5% P 2 O 5 , 5% ZnO towards murine osteoblasts (Balamurugan et al, 2007). In a companion paper, we presented evidence of good bioactivity and cytocompatibility for a 58S-based bioglass with the following composition: 59.7 mol% SiO 2 -36.2 mol% CaO -3.8 mol% P 2 O 5 -0.3 mol% (0.4 wt%) ZnO (58S-Zn0.4) (Bini et al, 2009). In the same paper we showed that the addition of larger quantities of ZnO resulted in increased cytotoxicity vs. SAOS-2 cells.…”

“…All of the SBF test steps were performed in a lamellar flow fume hood to maintain sterility. At the end of each treatment time, the amount of the HCA phase was determined by X-ray diffraction (Bini et al, 2009).…”

“…1 shows the weight percentages of the HCA crystalline phase, as determined by Rietveld refinement of the X-ray diffractograms, vs. the immersion time in SBF. For a detailed discussion on the limitations of the Rietveld analysis and related errors see Bini et al (2009). Pure silica displayed no HCA formation following treatment with SBF.…”