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Updated: Mar 26, 2026

Atomic Force Microscopy Imaging and Force Spectroscopy of Supported Lipid Bilayers
Published on: July 22, 2015
Water activity in lamellar stacks of lipid bilayers: "Hydration forces" revisited
R Leite Rubim1,2, B B Gerbelli1, K Bougis1,2
1Instituto de Física-GFCx, Universidade de São Paulo, P.O.B. 66318, SP 05314-970, São Paulo, Brazil.
Abstract:
Water activity and its relationship with interactions stabilising lamellar stacks of mixed lipid bilayers in their fluid state are investigated by means of osmotic pressure measurements coupled with small-angle X-ray scattering. The (electrically neutral) bilayers are composed of a mixture in various proportions of lecithin, a zwitterionic phospholipid, and Simulsol, a non-ionic cosurfactant with an ethoxylated polar head. For highly dehydrated samples the osmotic pressure profile always exhibits the "classical" exponential decay as hydration increases but, depending on Simulsol to lecithin ratio, it becomes either of the "bound" or "unbound" types for more water-swollen systems. A simple thermodynamic model is used for interpreting the results without resorting to the celebrated but elusive "hydration forces".
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