Histological and physico-chemical analyses on transformations of some bioactive glasses implanted in long bones of rabbit and sheep

Rods of a Hench-type and AKRA 15 glasses, and steel cylinders and plaques coated with AKRA 15 were implanted for various periods of time in long bones of rabbit and sheep. The sections of undecalcified, methacrylate embedded segments of bone containing the prostheses, were analyzed under optical microscope, scanning electron microscope, X-rays microprobe and on microradiographs. It resulted that there is: a) a direct contact of bone with the most part of Hench rods; b) an envelope made up of cortical bone surrounding the external part of AKRA rods and completely the coated-steel prostheses; c) a centrifugal diffusion of the main elements of the glasses in the degraded layer, towards the biological environment; d) a centripetal diffusion in the degraded layer, from the surrounding tissues, of Calcium and Phosphorus in the Hench-type glass and, in the AKRA 15 glass, also of Potassium. These results are discussed in relation to the ions that should be taken into account in preparing bioactive glasses.