A D V A N C E D M A T E R I A L S & P R O C E S S E S | O C T O B E R 2 0 2 2 4 2 Shape Memory and Superelasticity: Advances in Science and Technology (SMJ) is the official journal of the International Organization on Shape Memory and Superelastic Technologies (SMST), an affiliate society of ASM International. The journal publishes original peer-reviewed papers that focus on shape memory materials research with contributions frommaterials science, experimental and theoretical mechanics, physics with cognizance of the chemistry, underlying phases, and crystallography. It also provides a forum for researchers, scientists, and engineers of varied disciplines to access information about shape memory materials. These articles were taken from our June 2022 special issue on Nitinol Cardiovascular Devices and were selected by Shape Memory Editor-in-Chief Huseyin Sehitoglu. SMJ is available through springerlink.com. For more information, visit asminternational.org/web/smst. June 2022 OXIDE LAYER FORMATION, CORROSION, AND BIOCOMPATIBILITY OF NITINOL CARDIOVASCULAR DEVICES Srinidhi Nagaraja, Ronald Brown, David Saylor, and Andreas Undisz Nitinol-based cardiovascular devices can undergo corrosion following placement in the body and the resulting corrosion events may have potential implications on the mechanical integrity and biocompatibility of the device. This review article summarizes the critical factors that influence the degree to which Nitinol devices are susceptible to in vitro and in vivo corrosion, the extent of nickel release from the device, and the potential adverse biological effects following nickel release from the device. In particular, local and uniform corrosion resistance of the device is related to the quality of the protective surface oxide layer that is established by heat treatments and common surface processing techniques during device fabrication. Further, Nitinol implants in the cardiovascular system may be subjected to mechanical loading (pre-strain, fatigue, and fretting) and interact with different metals that can impact the corrosion behavior of the material. Biological responses that may occur following nickel release from Nitinol devices, such as cytotoxicity, thrombus formation, local effects on vascular tissue, systemic effects, and hypersensitivity, are discussed in this review. In addition, the use of computational bio- kinetic models in the absence of experimentally derived data to estimate local and systemic nickel concentrations in the body is discussed (Fig. 1). June 2022 PRE-STRAIN AND MEAN STRAIN EFFECTS ON THE FATIGUE BEHAVIOR OF SUPERELASTIC NITINOL MEDICAL DEVICES A.R. Pelton, B.T. Berg, P. Saffari, A.P. Stebner, and A.N. Bucsek There is a growing body of evidence that “in situ” modification of the microstructure of Nitinol due to pre-strain and mean strain strongly influence the fatigue properties of implanted medical devices and often, counterintuitively, for the better. The purpose of this review paper is to focus on the experimental evidence and to support these findings with micro-mechanical and metallurgical references. Prestrain effects are well recognized in Nitinol thermal actuator fatigue behavior and applied in medical device applications, but the effects of mean strain remain controversial. Detailed SMJ HIGHLIGHTS Fig. 1 — Pitting observed in explanted thermally oxidized Nitinol stents after six months in porcine iliac artery (unpublished images from Sullivan et al. 2017 study). 1 4
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