Please join the Chemical and Biological Engineering Department for a guest seminar with Professor Charles Schroeder on Thursday, March 2nd at 11AM in Tech Room L361.
Non-equilibrium dynamics of lipid vesicles in precisely controlled flows
Charles M. Schroeder
Department of Chemical and Biomolecular Engineering
Department of Materials Science and Engineering
University of Illinois at Urbana-Champaign
Abstract
Vesicles are membrane-bound containers that play an integral role in biological processes and biotechnology. In recent years, we have witnessed the societal impact of research in lipid-based RNA delivery with the deployment of the COVID-19 vaccine. Despite recent progress, we do not fully understand how the materials properties of lipid membranes affect the mechanics and transport properties of vesicles, especially under non-equilibrium conditions. In this work, we study the non-equilibrium dynamics of giant unilamellar vesicles in precisely defined flows using a Stokes trap, which is a new method to manipulate particles using active feedback and flow control. In this way, we directly observe non-equilibrium vesicle shapes as a function of dimensionless flow strength (capillary number, Ca) and vesicle deflation (reduced volume) using fluorescence microscopy. Remarkably, vesicles are found to be highly deformable objects that undergo reversible deformation in the bending-dominated regime, with deformed aspect ratios >20 in repeated stretch-relax cycles. Vesicles deform through a wide range of conformations in flow, including asymmetric and symmetric dumbbells, in addition to pearling, wrinkling, and buckling instabilities depending on membrane properties. We determine a precise flow-phase diagram for vesicles in Ca-reduced volume space using the Stokes trap. We further study the transient and steady-state stretching dynamics of vesicles in extensional flow. Unexpectedly, our results reveal a second shape transition for vesicle deformation defined by a second critical capillary number. We further identify two distinct relaxation processes for deformed vesicles, revealing two characteristic time scales: a short timescale corresponding to bending modes and a long timescale dictated by the relaxation of membrane tension. Finally, we study vesicle shape dynamics in large-amplitude oscillatory extensional (LAOE) flow, including numerical simulations and experiments. Our results reveal three distinct dynamical regimes - pulsating, reorienting, and symmetrical deformations - based on the competition between flow and membrane deformation timescales. Overall, our results provide new insights into the non-equilibrium flow-driven shape instabilities for vesicles using new experimental methods based on the Stokes trap.
Brief Bio
Charles Schroeder is the James Economy Professor in the Department of Chemical & Biomolecular Engineering and the Department of Materials Science and Engineering at the University of Illinois at Urbana-Champaign. He is Chair of the AI for Materials Group in the Beckman Institute for Advanced Science and Technology and holds affiliate status in the Department of Chemistry, Department of Bioengineering, Center for Biophysics and Quantitative Biology, the Carl R. Woese Institute for Genomic Biology, and the Materials Research Lab. He previously served as Associate Head in ChBE at Illinois. Dr. Schroeder received his B.S. in Chemical Engineering from Carnegie Mellon University in 1999, followed by an M.S. in 2001 and Ph.D. in 2005 in Chemical Engineering from Stanford University under the supervision of Professors Eric Shaqfeh and Steve Chu. Before joining Illinois in 2008, he was a postdoctoral fellow in the Department of Chemistry and Chemical Biology at Harvard University. Professor Schroeder has received several awards, including a Packard Fellowship for Science and Engineering, a Camille Dreyfus Teacher-Scholar Award, an NSF CAREER Award, the Arthur B. Metzner Award from the Society of Rheology, the Dean’s Award for Excellence in Research at Illinois, and an NIH Pathway to Independence Award (K99/R00). In 2022, he was elected a Fellow of the American Association for the Advancement of Science (AAAS Fellow).
Bagels and coffee will be provided at 11am, and the seminar will start at 11:10am. Please plan to arrive on time to grab a bagel and mingle!
