BIOACTIVE DOUBLE GLASS COATINGS FOR CO-CR-MO ALLOY

Glass compositions for double coatings for a Co-Cr-Mo alloy were devel oped. The glass compositions were chosen to fulfil such requirements a s matching thermal expansion, low glass transition temperature and mod erate solubility. For the ground coat a fairly high durability is requ ired, whereas the cover coat must be bioactive, i.e. become attached t o living bone by a chemical bond. Two compositions of each type were d eveloped by computer-aided optimization. The glasses were chosen in th e Na2O-CaO-B2O3-Al2O3-SiO2-P2O5 system. The bioactivity was tested in vitro by immersion in a simulated body fluid. The double coatings on C o-Cr-Mo alloy released hexavalent chromium into the solution as detect ed by yellow colouration and spectrophotometry. This colouration was s trong at the margin between coated and uncoated metal and may be expla ined by oxidation of trivalent chromium of the alloy in the presence o f glass. The released chromium did not have any notable effect on the calcium phosphate formation. After replenishing the solution no colora tion was observed. This suggests that the chromate is easily dissolved and that it may be possible to wash it out prior to implantation.