Evaluation of NaOH pre-treatment on the corrosion behavior and surface characteristics of hydroxyapatite coated NiTi all
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Evaluation of NaOH pre‑treatment on the corrosion behavior and surface characteristics of hydroxyapatite coated NiTi alloy G. M. Simsek1 · M. Ipekoglu2 · G. G. Yapici1 Received: 19 June 2020 / Accepted: 23 July 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract 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. Keywords NiTi · Coating · Hydroxyapatite · Corrosion · Cell viability · Surface wettability
1 Introduction Nickel-titanium (NiTi) shape memory alloys are increasingly utilized in biomedical fields such as orthopedic [1–3], dental [4] and cardiovascular [5, 6] applications owing to their superior properties including shape memory effect, super-elasticity and reasonable biocompatibility [7]. Having a large force to size ratio and being easily applicable in small dimensions render NiTi wires a favorable material for particular medical applications that require limited operational area and faster implantation. Although NiTi has been utilized very widely in biomedical applications, Ni release is still arguably the most fundamental concern of using NiTi alloys as an implant material. One promising approach to * G. G. Yapici [email protected] 1
Department of Mechanical Engineering, Faculty of Engineering, Ozyegin University, 34794 Istanbul, Turkey
Department of Mechanical Engineering, Faculty of Engineering, Turkish-German University, 34820 Istanbul, Turkey
2
inhibit or mitigate Ni leaching is to coat the implant surface with hydroxyapatite (HA) since it shows enhanced corrosion resistance and high resemblance to bone tissue and provides a strong interface [8]. This coating approach aims to obtain a synergistic effect combining extraordinary mechanical and functional properties of Ni
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