Abstract: The mechanical properties of biological tissues change over time and with disease progression. Quantifying these mechanical properties can thus be instrumental for medical diagnosis and for evaluation of tissue viability for transplant. However, it is exceptionally challenging to mechanically characterize soft and biological materials using conventional testing methods, especially in-vivo. In recent years, volume controlled cavity expansion (VCCE) has emerged as a powerful needle-based method for quantifying the nonlinear properties of soft materials in-situ. In this talk, after briefly revisiting the fundamentals of VCCE, I will describe the translation of VCCE into Digital Palpation (DP); a minimally invasive diagnostic tool offering a quantitative alternative to a clinician's sense of touch. I will describe the application of DP for testing in human tissue and will focus on an ex-vivo study of 36 tests in freshly resected human thyroid nodules. I will show how data from this rapid and minimally invasive mechanical test enables separation between benign and malignant nodules of this highly prevalent cancer and can even hint at resolving oncocytic and follicular sub-types that routinely confound existing diagnosis methods. At present, up to one third of thyroid nodules cannot be decisively classified, leading to avoidable surgical removal of the thyroid gland. We hope that these results can, in the future, help to reduce the large fraction of thyroidectomies (40-70%) that ultimately prove benign and thus avoidable; potentially relieving patients from the potential life-long implications of surgical complications and hormone replacement, and paving the way for the diagnosis of additional diseases.

Bio: Tal Cohen is an Associate Professor at MIT. She joined the Department of Civil & Environmental Engineering in November 2016 and has a joint appointment in the Department of Mechanical Engineering. She received both her MSc and PhD degrees in Aerospace Engineering at the Technion in Israel. Following her graduate studies, Tal was a postdoctoral fellow for two years at the Department of Mechanical Engineering at MIT and continued for an additional postdoctoral period at the School of Engineering and Applied Sciences at Harvard University. Cohen is a recipient of the 2023 Eshelby Mechanics Award, she received the ONR Young Investigator award and the NSF CAREER award in 2020, and the ARO Young Investigator award in 2019. Earlier awards include the MIT-Technion Postdoctoral Fellowship, and the Zonta International Amelia Earhart Fellowship. Her research, which combines both theoretical and experimental tools, is broadly aimed at understanding the nonlinear mechanical behavior and constitutive sensitivity of solids. This includes behavior under extreme loading conditions, involving propagation of shock waves and dynamic cavitation, material instabilities, and chemo-mechanically coupled phenomena such as material growth. Among various contributions, Cohen's research group developed the Volume Controlled Cavity Expansion

(VCCE) method; a minimally invasive technique for measuring local nonlinear mechanical properties of soft and biological materials. VCCE is currently being applied in human tissue for disease research and diagnosis.