Surface modification of hydroxyapatite to avoid bacterial adhesion

Hydroxyapatite was surface-modified by adsorption of nonionic polymers carrying phosphate groups as anchoring groups. A combination of alcohol ethoxylate and alkyl phosphate was also used. The possibility of interfering with early microbial colonization on apatite, mimicking the tooth surface, was investigated using radiolabelledStreptococcus mutans as model bacteria. The polymers, a nonionic cellulose ether and an EO/PO block copolymer based on polyglycerol as starting alcohol, were effective in buffer but gave only limited reduction of bacterial adhesion when the apatite had been pretreated with saliva. A 11 molar mixture of alcohol ethoxylate and alkyl phosphate was effective both with and without saliva, however. Studies with¹⁴C-labeled compounds, as well as microelectrophoresis experiments, indicate that an unsymmetrical double layer is formed on the apatite surface with predominantly alkyl phosphate in the inner layer and with alcohol ethoxylate pointing towards the water phase.