Issue Date: February 3, 2014
‘Pruney’ Skin Physics Revealed
We’re all familiar with the wrinkled, “pruney” skin we get from spending too much time in a bath or pool. A theoretical study provides new details about what happens when our outer skin cells absorb water, causing skin to look shriveled (Phys. Rev. Lett. 2014, DOI: 10.1103/physrevlett.112.038102). The cells in that outer layer contain so-called keratin intermediate filaments that have a helical structure and are hydrophilic. The filaments are interwoven into an ordered, three-dimensional lattice. Studying the thermodynamics of water-induced filament lattice swelling, Myfanwy E. Evans of the University of Erlangen-Nürnberg and Roland Roth of the University of Tübingen, both in Germany, found that the swollen state sits in a global energy minimum: Given water, the lattice will expand, although there is a limit to how far the filaments will stretch. Unlike the hard keratin in hair and nails, the filaments in skin are not cross-linked and instead have a thin layer of water between them that serves as lubrication. As the structures absorb water and swell, the stretching of filaments induces tension, akin to stretching a spring. Consequently, only a small force, such as that provided by water evaporation, is necessary for the lattice to shrink back to its “dry” state.
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