Modifying NiTi shape memory alloys to reduce nickel ions release through ethylenediamine plasma polymerization for biomedical applications

Abstract

Shape memory alloys (SMAs)-a type of smart materials- offer unique benefits for constructing unique medical implants, especially for heart stents, vertebral nails, and braces. One of the widespread SMAs is nitinol (NiTi) which exhibits extraordinary shape memory ability to recover its initial form. However, due to the result of nickel (Ni2+) ions release, long-term usage of NiTi alloys would pose allergic and carcinogenic risks in orthopedics and clinical applications. To tackle these hurdles, we here demonstrate a surface modification technique via plasma polymerization in order to minimize Ni2+ ions release. NiTi substrates were initially exploited by plasma polymerization of ethylenediamine (EDA) with varying power values (25-50-75-100 W) and time rates (5-10-15 min) in order to assess the most efficient parameters for minimal toxic metal release. The samples were then tested for 14 days in a biomimicked media. As a result, 75 W-10 min plasma polymerized sample reduced Ni2+ ions release by 57.18 % compared to the base specimen. These results offer a significant outcome in deploying NiTi alloys into the biomedical field more safely through surface modifications using the plasma polymerization technique.