Influence of electrochemical parameters on the characteristics of sono-electrodeposited calcium phosphate-coated carbon fiber cloth

In this work, we show that sono-electrodeposition is an efficient and versatile process for the coating of activated carbon fiber cloth (ACC) with biocompatible calcium phosphate (CaP) phases. The chemical composition, microtexture and structure of the coating were investigated by FTIR, SEM, TEM, XRD and solid-state NMR, highlighting the influence of cathodic polarization and water electrolysis on the coating characteristics. At low current density, the process leads to the formation of calcium-deficient hydroxyapatite (CDA) and octacalcium phosphate (OCP) phases with plate-like microtextures. At higher current density, the CaP coating consists of carbonated hydroxyapatite with a needle-like microtexture while, at intermediate regimes, both plate-like and needle-like microtextures are formed. The coatings were not uniform, however, for all the current density values employed, either on carbon fiber or ACC surfaces. Alternatively, it is shown that a uniform coating with a well-defined thickness can be obtained by using a constant potential value close to that of water electrolysis. In that case, the deposit consists of a homogeneous CDA phase with a plate-like nanocrystalline microtexture which exhibits a highly biomimetic structural character.