This award will support an experimental and numerical study of the dynamics of vesicles, particles composed of liquid or gas that is surrounded by a membrane, suspended in flow. The vesicles in this project are liquid-filled and are surrounded by a lipid bilayer membrane, which makes them similar to vesicles found in biological systems. They are also similar to synthetic vesicles that are used in a variety of consumer products and foods. The goals of the project are to characterize dynamics of the vesicles in flow, to use the behavior of the vesicles to characterize their mechanical properties, and to study collisions between vesicles and their adhesion. To accomplish these goals, vesicles of known composition will be placed in a microfluidic cell that has multiple fluidic channels arranged to keep the vesicle stationary in the surrounding flow. The deformation of single vesicles and collisions among vesicles will be viewed through a microscope. The results of the project will enable practitioners to design robust and stable vesicles for use in products. The project team will participate in the Illinois iRise program, which works with teachers to develop hands-on experimental labs for K-12 and high school students. The team will also develop hands-on demonstrations for students from underrepresented groups participating in local Boys and Girls Clubs.
The dynamics of single vesicles will be studied in precisely controlled steady and oscillatory extensional flow. Parameters that affect vesicle shapes and the transition from stable to unstable shapes will be examined, including flow rate, membrane bending energy, membrane elasticity and viscosity. A phase diagram for vesicle stability and deformation in extensional flow will be constructed. Results from the project will help resolve discrepancies between experiments and simulations regarding the onset of vesicle shape instabilities such as pearling. The oscillatory flow used in this project will expose vesicles to time-dependent strains, which will expose the effect of unsteadiness on shape instabilities. Collisions and adhesion of freely-suspended vesicles will be characterized. Most prior work has focused on the weak interaction limit, wherein the membrane bending energy plays a dominant role and membrane elasticity is not relevant. However, vesicle membranes deform and stretch upon collision, which has been predicted to give rise to enhanced interactions and unexpected aggregation. The experiments in this project will study collision and adhesion under these conditions.
