Nitinol shape memory alloy (NiTi SMA): Materials and applications in medical devices

The selection of materials for biomedical applications is governed by stringent requirements, including biocompatibility, biological safety, corrosion resistance, and mechanical compatibility with human tissues. Among metallic biomaterials, equiatomic nickel-titanium shape memory alloys (NiTi SMAs), commonly known as Nitinol, have attracted significant attention for medical device applications due to their unique functional properties, particularly super elasticity (SE) and the shape memory effect (SME), which distinguish them from conventional alloys. These functional behaviors originate from reversible stress- and temperature-induced martensitic phase transformations, enabling the material to undergo large deformations and recover its original shape without permanent damage. This unique mechanism allows Nitinol to exhibit exceptional flexibility and durability under physiological conditions. Furthermore, compared with conventional metallic biomaterials, Nitinol demonstrates a relatively low elastic modulus closer to that of cortical bone, while maintaining high strength. This review provides a focused overview of recent advances in Nitinol alloys, emphasizing their functional characteristics, underlying mechanisms, and applications in biomedical devices such as stents, guidewires, and orthodontic arch wires. In addition, the manuscript briefly discusses current challenges associated with NiTi biomaterials, and highlights existing strategies aimed at improving their reliability in biomedical applications.