Materials Properties and Manufacturing Processes of Nitinol Endovascular Devices

Both shape memory alloy and superelastic properties of nitinol material have attracted substantial attentions in a wide range of medical applications, specifically endovascular devices. The device could be collapsed in a low profile with cooling (i.e., ma

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Materials Properties and Manufacturing Processes of Nitinol Endovascular Devices Moataz Elsisy and Youngjae Chun

4.1  Background on Nitinol 4.1.1  History of Nitinol Shape memory behavior was first discovered in gold–cadmium (AuCd) alloy by Dr. Olander in 1932. The deformed AuCd alloy material in low temperature regains its original shape with the applied heat [1]. Many other alloys, such as CrMn, FePt, BaTiO3, and CuMn, were synthesized to achieve similar phase transformation behavior [2]. By late 1950s at the US Naval Ordnance Laboratory, Buehler and his colleagues discovered the shape memory behavior in nickel–titanium (NiTi) alloy while they worked on intermetallic compounds for heat shielding of missiles [2–4]. Nitinol is referred as NiTi in Ordnance Laboratory and became popular in various fields including aerospace, medical, and other industries due to its inexpensive cost for manufacturing and reliable performance. Nitinol has another unique property, superelasticity, in addition to shape memory behavior. Kurdiumov discovered superelastic behavior of metallic alloys in 1948 by investigating the elastic response of alloys that exhibit phase transformation upon varied stress levels applied on materials [5]. Nitinol has become one of the attractive alloy materials in numerous applications due to two unique properties, shape memory behavior and superelasticity. Currently available commercial products include buckling-resistant antennas, pipe-coupling devices, and eyeglass frames, which utilize superelastic behavior of nitinol [6]. There are more advanced types of applications that use shape memory behavior, which include light structure and engine rotors for aircrafts, biomedical robots, and micro-actuators. More recently, nitinol has been widely used in various medical M. Elsisy · Y. Chun (*) Department of Industrial Engineering, Bioengineering, University of Pittsburgh, Pittsburgh, PA, USA e-mail: [email protected]; [email protected] © Springer Nature Switzerland AG 2021 P. J. Bártolo, B. Bidanda (eds.), Bio-Materials and Prototyping Applications in Medicine, https://doi.org/10.1007/978-3-030-35876-1_4

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applications. Dr. Andreasen has developed the first nitinol biomedical application for an orthodontic device utilizing the superelastic behavior of nitinol. Other applications include implantable medical devices, such as endovascular and orthopedic devices [7–9]. Nitinol is specifically beneficial in transcatheter-based devices such as stents, percutaneous heart valves, and vascular occluders, and filters since these devices can be easily collapsed and inserted to a small diameter delivery catheter in low temperature, then deployed to its original shape and dimension in body temperature showing superelastic property after the device delivery.

4.1.2  Macroscopic Behavior of Nitinol 4.1.2.1  Shape Memory Effect Shape memory effect (SME) is the capability of the material, upon heating, to recover the permanent strain that occurs from the deformation in the martensitic phase [2]. N