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Membrane Elasticity in Giant Vesicles with Fluid Phase Coexistence

T. Baumgart ^*, S. Das , W. W. Webb ^* and J. T. Jenkins 

^* Applied and Engineering Physics, and Theoretical and Applied Mechanics, Cornell University, Ithaca, New York

Correspondence: Address reprint requests to Watt Wetmore Webb, Cornell University, 223 Clark Hall, Ithaca, NY 14853. Tel.: 607-255-3331; Fax: 607-255-7658; E-mail: www2{at}cornell.edu.

Biological membranes are known to contain compositional heterogeneities, often termed rafts, with distinguishable composition and function, and these heterogeneities participate in vigorous transport processes. Membrane lipid phase coexistence is expected to modulate these processes through the differing mechanical properties of the bulk domains and line tension at phase boundaries. In this contribution, we compare the predictions from a shape theory derived for vesicles with fluid phase coexistence to the geometry of giant unilamellar vesicles with coexisting liquid-disordered (L_d) and liquid-ordered (L_o) phases. We find a bending modulus for the L_o phase higher than that of the L_d phase and a saddle-splay (Gauss) modulus difference with the Gauss modulus of the L_o phase being more negative than the L_d phase. The Gauss modulus critically influences membrane processes that change topology, such as vesicle fission or fusion, and could therefore be of significant biological relevance in heterogeneous membranes. Our observations of experimental vesicle geometries being modulated by Gaussian curvature moduli differences confirm the prediction by the theory of Juelicher and Lipowsky.

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