Biocompatibility of hydroxyapatite coatings deposited by pulse electrodeposition technique on the Nitinol superelastic alloy.

The present study deals with pulse electrochemical deposition of HA on NiTi alloy and in vitro evaluation of coatings. At first step, a thermo-chemical surface modification process was applied to control the Ni release of the alloy. The electrochemical deposition of CaP coatings was examined at both dilute and concentrated solutions. The morphology and the composition of coatings were studied using scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). Plate like and needle like morphologies were formed for dilute and concentrated solution respectively and HA phase was formed by increasing the pulse current density for both electrolyte. The thickness of the samples was measured using cross sectioning technique. Fibroblast cell culture test on the coated samples revealed that the HA coating obtained by dilute solution shows the best biocompatibility. Also, MTT assay showed the highest cell density and cell proliferation after 5days for the HA coating of dilute solution. The contact angle of samples was measured and the coated samples showed a hydrophilic surface. Soaking the sample in SBF revealed that the crystallization rate of calcium-phosphate compounds is higher on the plate like HA coating as compared to the needle like morphology. The P release of the HA coated samples was measured in a physiological saline solution and the results show that the ions releasing in the plate like coating are less than the needle like coating. It seems that the stability of the plate like coating in biological environments is responsible for the better biocompatibility of the coating.

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-50.9 Ni 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.