Paper Number
VP47 

Session
Pre-recorded Flash Presentations (virtual)

Title
Non-linear transient stretching and relaxation of highly deformed vesicles reveals a deflation-dependent bending modulus

Presentation Date and Time
All Week (Asynchronous) Any Time

Track / Room
Pre-recorded Presentation / Virtual

Authors (Click on name to view author profile)

1. Schroeder, Charles M. (University of Illinois at Urbana-Champaign, Chemical and Biomolecular Engineering)
2. Kumar, Dinesh (University of Illinois at Urbana-Champaign, Chemical and Biomolecular Engineering)

Author and Affiliation Lines (in printed abstract book)
Charles M. Schroeder and Dinesh Kumar
Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801

Speaker / Presenter 
Schroeder, Charles M.

Keywords
experimental methods; biological materials; microfluidics; suspensions

Text of Abstract
Vesicles are membrane-bound soft containers that play a key role in biological processes. In this talk, we present new results on the non-equilibrium stretching and relaxation dynamics of phospholipid vesicles in precisely defined flows. Automated flow control (via a Stokes trap) is used to expose freely suspended vesicles to precisely controlled, time-dependent strain rate schedules in flow. In this way, we directly observe non-equilibrium vesicle shapes as a function of reduced volume, viscosity contrast, and Capillary number using fluorescence microscopy. Using this approach, we study the non-equilibrium stretching dynamics of vesicles, including transient and steady state stretching dynamics in extensional flow. Remarkably, vesicles are found to be highly deformable objects that undergo reversible deformation in the bending-dominated regime with deformed aspect ratios of >20-50 in repeated stretch-relax cycles. Quantitative analysis reveals that the steady-state deformation of vesicles in flow exhibits power-law behavior as a function of reduced Capillary number. We further developed an analytical model to determine the bending modulus of lipid membranes based on non-equilibrium steady-state conformational stretching data. Remarkably, our results show that phospholipid vesicles exhibit a deflation-dependent bending modulus, such that the membrane bending modulus decreases significantly as a function of reduced volume. Finally, we identify two distinct relaxation processes for vesicles stretched to high deformation, revealing two characteristic time scales: a short time scale corresponding to bending relaxation and a long time scale governed by membrane tension. Overall, our results provide new insights into the flow-driven shape dynamics for vesicles using new experimental methods in automated flow control and the Stokes trap.