Time dependent in vitro and in vivo surface layer formations on two bioactive glasses were compared. The goal was to calibrate the in vitro behaviour with in vivo observations from glass implants in bone and in soft tissue in rat. The follow-up times after implantation were one, four and eight weeks, after which the cross sectional surfaces of the glasses were analyzed with SEM/EDX. In SBF the layer development on the two glasses was similar. Layer thicknesses increased with immersion time. The layers consisted mainly of silica, but hydroxyapatite and a mixed layer of silica and hydroxyapatite formed with prolonged immersion. In vivo experiments indicated that the layer formation followed the same pattern as in vitro. However, in vivo the layers were more diffuse and mixed layers of silica and hydroxyapatite were observed on all samples.
