Functionalizing Surface Electrical Potential of Hydroxyapatite Coatings

While considerable work has been done on chemically functionalizing hydroxyapatite, little has been done on tailoring the electrical surface potential. This has been due to limitations in the available methods to impart a surface charge. Work to date has charged conventionally manufactured hydroxyapatite exhibiting a random crystal orientation. At the outset, the microstructure has not been optimized for the highest surface potential. The aim of this work was to both orient the crystals as well as fill the structure with hydroxyl ions for further increasing the surface electrical potential. We used hydroxyapatite coatings with the same topography, but different hydroxyl ion concentration; this altered the surface potential that was measured by Kelvin probe AFM. Results indicate that a greater hydroxyl ion concentration increases the surface potential of the hydroxyapatite coating. Coatings with a higher surface potential showed improved biological response, measured as osteoblast attachment and osteoblast related gene expression.