Electrochemical growth of composite hydroxyapatite coatings for controlled release

•A method was developed to trap ionic molecules into hydroxyapatite coatings during electrochemical synthesis.•The loading amounts and release kinetics of the ionic molecules were quantified.•Cationic and anionic molecules showed distinct loading and release behaviors.•The method can be used to create bioactive coatings for controlled release applications.

An electrochemical method was used to load ionic molecules into hydroxyapatite (HA) coatings during electrochemical synthesis. A metal cathode surface was first electrochemically coated with a thin layer of HA. Then, a second electrochemical coating step was conducted with non-reactive ionic molecules added to the synthesis solution. The loading and release from the HA films are driven in large part by the sign and valence of charge on the ionic additive. Cationic additives are attracted to the cathode surface and effectively loaded to form composite HA films, while anionic species are repelled from the cathode and not effectively incorporated. Divalent cations are released more slowly than monovalent cations. This simple method may be used to create drug eluting bioactive coatings for controlled release. The loading and release of streptomycin, a common antibiotic, was measured as a representative pharmaceutical example.