הנכם מוזמנים לסמינר של נוי כהן אורח בבית הספר להנדסה מכאנית
School of Mechanical Engineering Seminar
Monday, March 8, 2021 at 14:00
The mechanics behind the counter-intuitive behaviors of biological gels
Department of Materials Science and Engineering
Technion – Israel Institute of Technology
Hydrogels are formed when a polymer network is submerged in an aqueous environment. This process is referred to as swelling. In this talk, we will review the classical swelling theory and demonstrate its inability to capture the swelling response of two biological polymeric systems.
First, I will discuss the mechanical response of resilin, which is a rubber-like protein found in insects that exhibits a significant reduction in stiffness (of several orders of magnitude) upon swelling. This drastic softening effect cannot be explained by the volumetric changes that are associated with the pure swelling process and thus is not captured by the classical theories. Rather, the swelling response of resilin stems from its unique microstructure which comprises a large number of hydrogen cross-linking bonds that dissociate in the presence of water. I will introduce a microscopically motivated model that explains the origin of this response and captures experimental findings.
The second biological system that we will discuss is spider silk, which is an extraordinary protein material. In the dry state, spider silk is a highly aligned glassy polymer. Upon wetting, spider silk threads soften and experience supercontraction, i.e., a significant shortening of up to ~60% in length. To explain this counter-intuitive response, I will present a model that shows this phenomenon stems from three factors: dissociation of hydrogen bonds due to an influx of water, loss of orientation, and swelling. This model is found to be in excellent agreement with experimental measurements.
The insights from these works can be used as a design guide that enables the fabrication of new bio-inspired synthetic polymers with unique and tunable properties.
Bio: Noy Cohen received his Ph.D. from the Ben-Gurion University in 2016. After two post-docs in the California Institute of Technology and the University of California Santa Barbara, Noy accepted an Assistant Professorship position at the Department of Materials Science and Engineering, Technion in the beginning of 2019. His research interests include multi-scale modelling of polymer networks and gels, mechanics of muscles, and 3D printing.