Endothelialization and the bioactivity of Ca-P coatings of different Ca/P stoichiometry electrodeposited on the Nitinol superelastic alloy

An alternative approach to improve the cardiovascular stents with less restenosis than drug eluting stents, involves an improvement in endothelialization of implants. In this study, the bio compatibility of the modified Ti-50.9Ni alloy was investigated. At the first step, a thermo-chemical surface modification process was used to control the Ni release of the alloy. XPS and Raman analysis revealed that the surface of the alloy contains titanium dioxide after the modification process. According to the Ni release test, this surface condition has a good durability in Ringer's solution and offers a standard range to the leached Ni. At the next step, porous Ca-P films were electrodeposited on the modified surface. The results of endothelial cell culture on the coated samples revealed that the Ca-P coating, which has the highest value of Ca/P ratio shows the best result. The coating revealed a moderately wettable surface with a water contact angle of 53.3°. According to Ca content analysis of the cell culture medium, this coating has the lowest amount of Ca as a result of minimum solubility of the coating. In the other Ca-P coatings with lower Ca/P ratios, the solubility of coatings results in the detachment of the cells. Also nano-indentation and SEM studies revealed that the low stiffness in the calcium deficient coating can result in the failure of the coating as a result of the tensions created by the cells.