(725a) The Swim Pressure: Forces and Stresses on Living Materials

To understand complex biological systems like the interior of a cell, it is essential to characterize the motion of molecular motors and the interaction of active constituents with other cellular components. Active elements like motor proteins generate internal forces and stresses that enable them to control their own behavior and that of their surroundings, driving the cell far from equilibrium. In an effort to model the cell, we developed a method to encapsulate swimming Janus particles, microorganisms, and other nano/micron-sized objects inside of a phospholipid vesicle. We use a new â??swim pressureâ? perspective to analyze the mechanical deformation and lysis of cells triggered by the motion of active elements and pathogenic bacteria. We further fabricate soft, flexible materials that can expand/shrink, elongate, move, and steer on command by loading the material with bacteria that can move in a directed, coherent manner. These soft materials may be used as micro- or nanomechanical devices and motors that could have multiple applications in medicine (e.g., focused drug delivery), biophysics, and other fields. In addition to being a useful rheological tool to quantify the mechanical forces, stresses, and (thermo)dynamics of active elements inside a cell, the swim pressure concept may engender new discoveries in cellular morphology, function, and the complex intracellular transport within the cytoplasm.