Porous bioactive glass and glass-ceramics made by reaction sintering underpressure

A glass and a rhenanite-wollastonite glass-ceramic were synthesized with th e qualitative composition Na2O-CaO-SiO2-P2O5. Both materials were prepared by reaction sintering under isostatic pressure (RSIP) using powder mixtures Solid state reactions were complete within a few hours at 950 degreesC und er modest pressure. Formation of the glass and crystalline phases was drive n by an intermediate, reactive, low viscosity Na2O-SiO2 phase. A reaction m echanism is suggested. Porous materials were obtained with two ranges of po re sizes: 100-200 mum and less than or equal to5 mum in diameter. The glass and the glass-ceramic were corroded in simulated body fluid at 37 degreesC . The evolution of surface features was studied. Gel layers formed on both materials. Corrosion was fastest inside the pores. Microcrystals of apatite were identified by crystal structure analysis and by chemical analysis. Du ring corrosion of the glass-ceramic, rhenanite most likely was converted in to apatite. Comparison of these results with published information suggests that the glass and glass-ceramic are bioactive. We suggest that RSIP can b e used (a) to control the surface porosity and pore size of bioactive impla nts, thereby increasing the stability of tissue/implant interfaces; (b) to make glasses and glass-ceramics with new properties; and (c) to make near n et-shape materials. (C) 2000 John Wiley & Sons, Inc., J Biomed Mater Res 54 : 320-327, 2001.