Hydroxyapatite coating on a cobalt base alloy by investment casting

A cobalt alloy was cast into preheated molds previously coated with hydroxyapatite powder. Two molds were used, one made of investment material and the other of pure graphite. Selected samples were heat treated. Both heat and non heat treated samples were immersed in simulated body fluid for 21 days at 37 °C. A ceramic layer, identified as hydroxyapatite, was formed on all the samples. A thicker layer was formed on the sample cast into the investment mold without heat treatment. A chemical interaction between the investment mold and hydroxyapatite takes place leading to a higher in vitro bioactivity.