Metals with Memory: Minimally Invasive Biomedical Devices

Speaker

Samantha Daly, Ph.D.
Professor
Department of Mechanical Engineering
University of California, Santa Barbara

Abstract

The metallic alloy Nickel-Titanium (trade name Nitinol) is used extensively in biomedical applications due to its unique superelastic properties, which allow for the minimally invasive insertion and deployment of devices inside the body. However, Nitinol is a particularly complex structural material that undergoes highly localized deformations, due to a phase transformation between two different atomic lattice structures that underlies its superelastic ability. The unusual behavior of Nitinol is not fully characterized nor well understood, which seriously hinders the predictively modelling of these devices under the complex loading conditions encountered inside the body. This talk will discuss recent work to address this knowledge gap through experimental studies into the deformation mechanisms of Nitinol across length scales as a function of applied load state, crystallographic texture, and mechanical cycling. The examination of locally active transformation and its impact on the use of Nitinol in biomedical devices will be discussed, including the discovery of a remarkable transformation memory under cyclic loading. The unexpected formation of a ferromagnetic subsurface oxide under certain heat treatments will also be discussed, highlighting the need for heat treatment standards on Nitinol for MRI safety. The development of a novel methodology to quantitatively map full-field deformations at high (nm) spatial resolution across large, mm-scale fields of view will additionally be presented in the context of these experiments..

Bio

Samantha (Sam) Daly is a Professor in the Department of Mechanical Engineering at the University of California at Santa Barbara. She received her Ph.D. from Caltech in 2007 and subsequently joined the University of Michigan, where she was on the faculty until 2016 prior to her move to UCSB. The Daly group investigates the mechanics of materials, with a focus on the fatigue and fracture of metallic alloys and advanced composites, and new experimental and machine learning approaches for materials characterization and discovery. Her recognitions include the Experimental Mechanics Best Paper of the Year Award, IJSS Best Paper of the Year Award, DOE Early Career Award, NSF CAREER Award, AFOSR-YIP Award, ASME Eshelby Mechanics Award, Journal of Strain Analysis Young Investigator Award, ASME Orr Award, and Caddell Award. She was recently elected to the Executive Board of the Society of Experimental Mechanics, and serves as an Associate Editor of the journals Applied Mechanics Reviews, Experimental Mechanics, and Strain.