BRITE Pivot: An Integrated Theory of Continuum and Statistical Mechanics of Active Soft Matter

Biological membranes are interfaces that separate cells and their internal organelles from their environment. These membranes inevitably play a crucial role in processes such as response of cells to mechanical stimuli, transmission of messages through electrochemical signals, or exchange of nutrients. To date, most studies have focused entirely on treating biological membranes as "passive" membranes that exhibit fluctuations due to thermal vibrations of molecules only. However, there is growing consensus that membranes are actually "active", which refers to their ability to harness energy from an extrinsic source to execute specific functions. This Boosting Research Ideas for Transformative and Equitable Advances in Engineering (BRITE) Pivot award supports fundamental research in understanding the mechanics of active membranes and furnishing insights into their role in critical biological phenomena. It is envisioned that this endeavor will pave the way to better understand, control, and perhaps mimic active biological matter for biotechnology and healthcare applications. The research will also train graduate students in a multidisciplinary area at the intersection of solid mechanics, fluid mechanics, statistical mechanics, and biophysics. It will enrich the curriculum at the PI's institution where over 50 percent of the student body is classified as belonging to underrepresented groups. The objective of this research is to establish a rigorous framework of continuum mechanics for active membranes by integrating it with non-equilibrium statistical mechanics. For decades, the field of continuum mechanics has provided remarkable insights into passive membranes by utilizing tools from equilibrium statistical mechanics which assumes the membranes to be in thermal equilibrium. However, active forces drive a membrane away from equilibrium. Furthermore, modeling of active fluctuations requires dynamic analysis of membranes embedded in a fluid that dissipates energy. These factors render conventional equilibrium statistical mechanics incapable of modeling active membranes. This research seeks to develop a new integrated theory to explain the mechanics of active membranes. Specifically, the PI will focus on three phenomena that are ubiquitous in biology – 1) entropic interactions between active membranes; 2) role of active fluctuations in vesicle size distribution, and 3) relaxation of electric fields in active membranes. The theoretical framework developed here will open avenues for the modeling of more complex biological phenomena by way of theory and computational methods and provide routes for designing controlled experiments to understand active soft matter. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.