Evaluation of the osteoblast response to a silica gel in vitro

Many bioactive glasses and glass ceramics contain silica, yet the effect of silica on the osteoblast is not well understood. The osteoblast cell response to a silica surface, without the interference of the other ions present in glasses and glass ceramics has been investigated. A silica sol-gel was prepared which gave a molar ratio of 1:4:4 tetraethyl orthosilicate (TEOS): ethanol:acidified water 0.2 M HCl) and spin cast on to thermanox discs. The gel was characterized in terms of bioactivity and release of silicic acid. Primary human osteoblasts (HOBs) were seeded on the surface of upright or inverted silica discs. Cell activity (alamar blue reduction), number (DNA content) and differentiation (alkaline phosphatase activity, nodule formation and mineralization) were measured. There was no apparant difference in cell number, activity or alkaline phosphatase activity between silica discs and controls. Nodules formed much earlier on the silica surfaces and these eventually mineralized. Nodule formation was reproducibly enhanced on the silica surface and less markedly on the inverted discs. It is likely that both the surface characteristics of the silica gel and silicic acid release from the disc affect osteoblast behaviour.