Controllable phase transformation of fluoridated calcium phosphate ultrathin coatings for biomedical applications

Abstract

Titanium has been widely used in medical implants for hard tissue replacements. Nevertheless, the bioinert innate oxide layer on the titanium implant surface usually makes the implant fail to osseointegrate with the surrounding tissue after surgery. To improve the bioactivity of titanium implants, the deposition of calcium phosphate (CaP) coatings attracts much research interest owing to the excellent bioactivity and biocompatibility of CaP. This work has successfully developed a promising synthetic method to prepare uniform fluoridated CaP coatings with ultrathin thicknesses (∼170 nm) and desired phases on acid-etched titanium (AETi) substrates. A dense ultrathin coating with a dominant phase of fluoridated amorphous CaP (FACP) can be obtained by an electrochemical deposition method in galvanostatic mode. After a heat treatment at 600 °C for 3 h in humid air, the as-prepared coating has been transformed to a coating with a dominant phase of fluoridated hydroxyapatite (FHA). Additionally, the dominant phase of the coating can be transformed from FACP to α-tricalcium phosphate (α-TCP) by a heat treatment at 800 °C for 3h in air. Unlike previously reported fluoridated CaP coatings with thicknesses of around several micrometers, the ultrathin thickness can potentially enhance the adhesive strength and ductility of the coating. Notably, the fluorine incorporation in the coating can bring in additional benefits such as lower solubility, higher antibacterial activity, and higher adhesive strength. The electrochemical deposition associated with different post heat treatments can obtain fluoridated CaP coatings with different desired phases in a controllable manner, which is very important since CaPs with different phases possess different properties and may be suitable for different biomedical applications. This study proposes a promising, simple, and low-cost method which can endow complex-shaped titanium implants with better bioactivity for dental and orthopedic applications.