DISSOLUTION AND SCANNING ELECTRON-MICROSCOPIC STUDIES OF CA,P PARTICLE-CONTAINING BIOACTIVE GLASSES

Calcium phosphate (Ca,P) precipitation behavior on the surface of two bioactive glasses and four bioactive glass composites-two with hydroxy lapafite (Ca10(PO4)6 (OH)2) and two with rhenanite (CaNaPO4)-were stud ied in simulated body fluid (SBF) and in Tris-Buffer at 5, 8, 16, 24, 48, 72, and 144 h. The weight loss of the materials was measured and t he amount of precipitation was estimated using scanning electron micro scopy with electrochemical detection (SEM-EDX) analysis. The test was repeated for one glass and its respective rhenanite composite every 3 h until 60 h and thereafter every 10 h until 150 h in SBF. Atomic abso rption spectroscopy, spectrophotometry, SEM-EDX analysis, and pH measu rements were performed on these samples. It is shown that in vitro the composite materials have a higher capacity for Ca,P precipitation tha n the glasses. Weight losses of the materials correlate well with thei r composition. Both the glass and Ca,P phases influence the precipitat ion mechanism and rate. Precipitation begins preferably from the glass phase. Ca,P particles clearly influence the time of onset and rate of precipitation. Cross-sectional EDX analysis of the samples revealed a n absence of a clear Si-rich layer in glass A0B0 (SiO2 53.9 mol %, Na2 O 27.5, CaO 12.4, P2O5 6.2, Al2O3 0.0 and B2O3 0.0) composites. This w as attributed to the presence of extra calcium and phosphate ions on t he surface of the material. The ion-concentration and pH change curves offered insight into the mechanism of precipitation. A connection was established between SEM-EDX results and the release curves. Formation of an Si,Ca,Na film was observed that seemed to initiate the CaP prec ipitation. It is speculated that it is a characteristic of this partic ular glass composition. Two possible models for the mechanism of Ca,P precipitation are discussed. Phosphate polycondensation with silicate network or Ca binding to silicate network can both explain the results and it is assumed that in general both mechanisms play a role in the precipitation process. (C) 1993 John Wiley & Sons, Inc.