Dissolution, leaching, and Al2O3 enrichment at the surface of bioactive glasses studied by solution analysis

Abstract
Five glass compositions in or near the bioactive region in the system SiO2Na2OCaOP2O5Al2O3 were studied in vitro by immersion in Tris buffer. The Si concentration can be taken as a measure of the amount of dissolved glass, whereas the Na concentration can be used to estimate the thickness of the Si-rich (Si gel) layer. Upon immersing a bioactive glass into Tris buffer, a surface layer of a few micrometer thickness is dissolved during the first 8 h. During the first few hours of immersion, the rate of dissolution of the glass network is equal to or exceeds that of the growth of the Si-rich layer. If the glass contains Al2O3, most of the aluminum that would be released due to dissolution of the silica network is enriched in the Si-rich surface layer that forms due to leaching. Al2O3 is not only bonded by the Si gel but also interferes with formation of culcium phosphate. © 1993 John Wiley & Sons, Inc.

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