Evaluation of NaOH pre-treatment on the corrosion behavior and surface characteristics of hydroxyapatite coated NiTi alloy
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Successful short-term implementation of nickel-titanium (NiTi) alloys as implants has been a motivation for the development of long-term applications. However, rendering these as safe implant materials is challenging. The major problem associated with the use of NiTi for in-vivo applications is the potential risk of Ni release from the implant surface due to the corrosive environment of the body. Various methods including surface treatment techniques with acid and alkali solutions and application of biocompatible coatings have been used to overcome these difficulties. In particular, NaOH pre-treatment has been commonly performed for surface activation of the substrate material to enhance the adhesion properties of coatings. The present work investigates the effect of NaOH pre-treatment on the hydroxyapatite (HA) coating and the resulting corrosion behavior of and cell response to HA coated NiTi wires. Microstructural examinations showed that the coating integrity deteriorated with prior NaOH treatment which also increased the corrosion rate as evidenced by potentiodynamic measurements. XPS analysis revealed heightened Ni levels on the sample surfaces and cytotoxicity tests showed decreased cell viability for the samples with pre-treatment. Absence of NaOH pre-treatment led to lower contact angle values pointing to higher biocompatibility.