Chemically encapsulated structural elements for probing the mechanical responses of biologically inspired systems

A living cell has a crowded environment with a dense distribution of molecules that requires structured organization for its efficient functioning. One component of this structure, the actin cytoskeleton, is essential for providing mechanical support and facilitating many response activities, including the contraction of muscle cells and chemotaxis. Whereas many investigations have provided insight into the mechanical response from either an in vivo or in vitro perspective, a significant gap exists in determining how the living cell response and the polymer physics response are bridged. The understanding of these systems involves studying their components, including the individual cytoskeletal elements versus the higher-order organism organization in a living cell. Here, we leverage this organization in nature by using a chemistry-based approach to mimic the cytoskeleton in an artificial environment composed of spherically distributed lipid bilayers. This construct bears similarities to the cell membrane. To create a structurally regulated environment, we encapsulate G-actin into giant unilamellar vesicles and then polymerize actin filaments within individual liposomes. We visualize these vesicles with epifluorescence microscopy and confocal microscopy. Atomic force microscopy is then used to probe the mechanical properties of these artificial cells. This polymer cytoskeletal network appears to connect with the lipid bilayer and span the internal space within the liposomes in a manner similar to what is observed in living cells. This work will have implications in a variety of fields, including chemistry, polymer physics, structural biology, and engineering mechanics.