Preparation of bone-like composite coating using a modified simulated body fluid with high Ca and P concentrations

A carbonate hydroxyapatite (HA)–collagen (Col) composite coating on NiTi shape memory alloy (SMA) was synthesized by biomimetic growth in modified simulated body fluid (MSBF), which containing high Ca and P ions concentrations. The morphology of composite coating was uniform and porous. The major phase of coating, identified by Infrared Spectroscopy (IR) and X-ray diffraction (XRD), was HA with B-type carbonate substitution. It was also proved by IR results that the collagen was present in the coating. Transmission Electron Microscopy (TEM) and high resolution TEM analysis showed that the c-axis of HA crystals aligned parallel to the longitudinal direction of the collagen fibrils. The relative orientation maintained in the composite coating may benefit the NiTi SMA to achieve better properties in hard tissue replacement.