Living systems like cells are often crowded with macromolecules, where a unique non-ideal force called depletion interaction emerges. In aqueous systems where macromolecules and large spatial compartments co-exist, the macromolecules will be excluded from the volume surrounding the compartments. Thus, the system encourages the large compartments to approach each other by exerting this entropic force, minimizing the excluded volume and maximizing the net entropy. Additionally, any disparity in the concentration of molecules across the compartment exerts another entropic force called osmotic stress. Together, these indirect, non-specific, and universal forces, namely osmotic stress and depletion interactions, have been widely found in cells and between biomolecules, affecting their shapes and interactions. We experimentally investigated how the entropic forces influence two typical synthesized biomembrane structures: giant unilamellar vesicles and cylindrically organized multilamellar myelin. We found that the synergistic influence of osmotic stress and depletion interactions drive division of single giant vesicles and induce an extended shape instability at the myelin-myelin interface. We propose that these shape, morphological, and topological transitions observed in artificial systems are guided by entropic forces, in a similar way that exists in living systems. Additionally, these synthesized membrane compartments can be developed as models to explain the phenomena observed in biology, and help with the bottom-up synthesis of artificial cells.

Entropic forces mediate topological division and shape instabilities in membrane compartments

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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