Collaborative Research: Fundamental Principles of Swimming in Viscoelastic Media

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Kudrolli 0853942Cell movements play a central role in a host of biological processes, such as fertilization, bacterial infection, and transport of mucus and fluid in the body. The complex fluids that motile cells encounter are laden with polymers. When deformed by a swimming cell, the polymers stretch, leading to an elastic resistance in addition to the viscous resistance of the fluid. The microstructure of biological materials is often anisotropic as well. The goal of this research is to use theory and experimental models to establish the fundamental principles of swimming in viscoelastic media such as mucus and biofilms. To study swimming mechanics in a controlled environment, the PIs will develop a series of table-top macroscopic scale experiments. These experiments will determine how swimming speed depends on viscoelastic properties for a swimmer with a prescribed stroke, how viscoelastic forces can alter the shape of a beating filament, and the role of viscoelasticity in the hydrodynamic synchronization of beating cilia. The PIs will develop new theories for these phenomena, and also study how non-Newtonian effects change the hydrodynamic interactions between nearby swimmers and boundaries, and the nature of the collective motion of dense populations of swimmers. The basic hydrodynamic theory for microorganisms swimming in a Newtonian liquid such as water has been largely established. Nevertheless, the field continues to be very active since many issues such as hydrodynamic interactions between cells, synchronized ciliary beating, and the actuation of flagella are only partially understood. The natural environments of microorganisms are predominantly non-Newtonian, and every basic element of the theory must be considered anew. Our work will also establish the design principles required to build artificial microswimmers capable of negotiating viscoelastic as well as viscous fluids. The PIs will work with the K-12 Teacher Training program within the Brown MRSEC outreach program to develop new demonstrations of cell motility. The PIs will continue to build on their successful history of recruiting under-represented groups. Finally, the fundamental principles of this work have the potential to impact applications such human fertility, the treatment of bacterial infections and diseases such as cystic fibrosis, and the artificial insemination of livestock.