Analysis of the in vivo reactions of a bioactive glass in soft and hard tissue.

A bioactive glass, S53P4, was implanted as granules subcutaneously in muscles and connective tissue of rabbits, as well as in the mandibular bone of a sheep. After the implantation period of 2-3 months, cross-sections were prepared and studied by scanning electron microscopy and energy dispersive X-ray analysis. The glass reacted essentially in the same way in all types of tissue. The granules consisted of an unreacted core and a reacted layer with a silica-rich and calcium phosphate-rich zone. Large hydroxyapatite crystals were occasionally found on top of the calcium phosphate surface of the granules implanted in soft tissue. On the basis of elemental analysis of the reaction layers it was found that the release of calcium from inside the glass is sufficient to account for the formation of the calcium phosphate surface layer, whereas the release of phosphate from the glass is not sufficient.