In vitro study on the integrity of a hydroxylapatite coating when challenged with staphylococci.

An in vitro study was performed to evaluate the effect of Staphylococcus aureus and Staphylococcus epidermidis on the integrity of a hydroxylapatite coating. The coating plasma-sprayed on poly(L-lactide), showed dissolution during a 24 h incubation period. This was indicated by an increase in pH and calcium release in the buffer solution. After 4 h of incubation, calcium levels decreased due to the precipitation of calcium phosphate complexes on the coating. The bacteria digested or dissolved the coating, creating irregularly shaped holes. Although the integrity of the hydroxylapatite coating was focally damaged within 2-4 h of incubation with staphylococci, the extent of the damage was only marginal. Due to the formation of a layer of CaP precipitates though, bacteria could not be counted accurately after 4-8 h of incubation. This model could reveal part of the failure mechanism of infected hydroxylapatite coated implants.