Physics

Dr. Sayantan Majumdar
James Franck Institute, the University of Chicago, USA

History-dependent adaptation is a central feature of learning and memory. Incorporating such features into ‘adaptable materials’ that can modify their mechanical properties in response to external cues, remains an outstanding challenge in materials science. In this talk, I will mainly describe a novel mechanism of mechano-memory in cross-linked F-actin networks, the essential determinants of the mechanical behavior of eukaryotic cells. We find that the non-linear mechanical response of such networks can be reversibly programmed through induction of mechano-memories. In particular, the direction, magnitude, and duration of previously applied shear stresses can be encoded into the network architecture. The ‘memory’ of the forcing history is long-lived, but it can be erased by force applied in the opposite direction. Our results demonstrate that F-actin networks can encode analog read-write mechano-memories which can be used for adaptation to mechanical stimuli. We further show that the mechano-memory arises from changes in the nematic order of the constituent filaments. These results suggest a new mechanism of mechanical sensing in eukaryotic cells and provide a strategy for designing a novel class of materials. In the last part of my talk I will briefly describe my other project on designing a completely different class of adaptive materials using shear induced dynamic jamming transition in dense particulate suspensions. Particularly, I will demonstrate how the jamming transition is mediated by a rapidly propagating shear induced jamming front probed using optical and ultrasound imaging. Apart from important fundamental interests, these systems have wide range of potential applications, particularly in designing flexible shock absorbing systems.