A feedthrough assembly of an implantable medical device includes a glass insulator containing at least approximately 20 mol % of calcium oxide (CaO), preferably of a CABAL-12 type composition. The assembly is either manufactured so that the glass insulator includes a surface layer including calcium phosphate, preferably of relatively low solubility, or is assembled in the implantable device so that the glass insulator is exposed to phosphate-containing body fluid, when the device is implanted, for the formation of a surface layer including calcium phosphate.
