In vitro transformation of bioactive glass granules into Ca-P shells

Bioactive glass (BG) granules of narrow size are excavated when implanted i n mandibular bone of beagles. Bone tissue forms within these internally hol lowed particles without a connection to the bone at the margins of the defe ct. In this study the internal excavation of BG granules was simulated by i n vitro immersion experiments. Postimmersion solutions were analyzed for ch anges in Si, Ca, and P concentrations. Using scanning electron microscopy ( SEM), energy dispersive X-ray (EDX) analysis and Fourier Transform Infrared (FTIR) spectroscopy, granules were analyzed for compositional, morphologic , and structural changes resulting from immersion. Only when the solution w as continuously replenished and only if this solution was composed of elect rolyte- and protein-containing serum was excavation achieved. Without solut ion replenishment, that is, under so-called integral immersion conditions, the solution quickly became saturated in silicon, and the silicon no longer dissolved. When the glass was immersed in a solution with serum, a porous surface structure with fine precipitates was formed, in contrast to a dense surface reaction layer with closely packed globular precipitates that was formed in a solution without serum. The combined effect of continuous solut ion replenishment and the use of a solution containing serum proteins led t o the formation of a surface reaction layer that did not impede continued c orrosion. As such, all Si was released, and eventually a hollow Ca-P shell was formed. Thus this study supports the hypothesis that there is a physico -chemical mechanism of Si transport through the Ca-P-rich layer followed by Si dissolution. This mechanism may be operative in vivo and thereby may co ntribute to the observed in vivo excavation. (C) 2000 John Wiley & Sons, In c.