Hydroxyapatite formation on a silicate and borate glass

Two glasses, 45S5 Bioglass® and 45S5B1, a borate glass with the same molar composition as 45S5, were reacted with phosphate containing solutions in vitro at 37°C, for the purpose of determining the possible bioactivity of 45S5B1. Both glasses reacted non-uniformly in 0.25 M and 1 M phosphate solutions such that hydroxyapatite formed on the surface of each glass in as little as 1 day on 45S5B1 and 14 days on 45S5. Hydroxyapatite formation on the surface of a glass by reaction with a solution was previously believed to be dependent on the presence of a silica gel layer. The present investigation revealed that hydroxyapatite would form on a borate glass surface by glass- solution reactions if the solution had a sufficient phosphate concentration. The hydroxyapatite that formed on the surface of 45S5B1 and 45S5 had a microstructure similar to that of the apatitic component of natural bone. Particles of 45S5 glass were also reacted with a physiological saline solution supplemented with newborn bovine serum. The surface reactions of 45 S5 particles in static, non-replenished solutions that contained bovine serum were slower than those in a corresponding solution without serum. When the solution was replenished, the reaction layer growth occurred at a rate (~10 µm/day) comparable to the reaction layer growth rate (~20 µm/day) in solutions without bovine serum --Abstract, page 2