Improved corrosion protection of titanium implant material by crystallographic texturing of Sr doped calcium phosphate electrodeposits

Abstract

Nanocrystalline calcium phosphate (CaP) coatings can provide biocompatibility and corrosion protection to biomaterials upon implementation in the human body. While the long term stability of recently developed coatings in biological environment proves to be challenging, the present work tailors the surface by orienting the growth (crystallographic texturing) of strontium doped CaP coatings in order to increase their corrosion resistance. X-ray diffraction (XRD) as well as selected area electron diffraction patterns from transmission electron microscopy reveal that nanocrystalline CaP crystallizes in hexagonal hydroxyapatite structure preferentially oriented along the c-axis. Orientation distribution function obtained from XRD texture studies confirms the presence of a [0001] fiber texture and the estimated texture index indicates the evolution of texture with increasing deposition current density. Polarization studies point out that increasingly textured coatings decrease the corrosion current density by an order of magnitude (from 2.43 × 10−7 to 3.46 × 10−8 A cm−2). Impedance measurements confirm that oriented growth of film renders improved corrosion resistance. This study demonstrates that oriented growth of electrodeposited films strongly improves the corrosion performance of titanium, which can be employed in design and development of highly corrosion resistive implant materials.