Letter abstract
Nature Materials 6, 48 - 51 (2007)
doi:10.1038/nmat1810
Subject Categories: Polymers | Biological materials | Mechanical properties | Computation, modelling and theory
Negative normal stress in semiflexible biopolymer gels
Paul A. Janmey1,2, Margaret E. McCormick1, Sebastian Rammensee1,3, Jennifer L. Leight1, Penelope C. Georges1 and Fred C. MacKintosh4
When subject to stress or external loads, most materials resist deformation. Any stable material, for instance, resists compression—even liquids. Solids also resist simple shear deformations that conserve volume. Under shear, however, most materials also have a tendency to expand in the direction perpendicular to the applied shear stress, a response that is known as positive normal stress1. For example, wet sand tends to dilate when sheared, and therefore dries around our feet when we walk on the beach. In the case of simple solids, elastic rods or wires tend to elongate when subject to torsion2. Here, we show that networks of semiflexible biopolymers such as those that make up both the cytoskeleton of cells and the extracellular matrix exhibit the opposite tendency: when sheared between two plates, they tend to pull the plates together. We show that these negative normal stresses can be as large as the shear stress and that this property is directly related to the nonlinear strain-stiffening behaviour of biopolymer gels3.
- Institute for Medicine and Engineering, University of Pennsylvania, 3340 Smith Walk, Philadelphia, Pennsylvania 19104, USA
- Department of Physics and Astronomy, University of Pennsylvania, 209 S 33rd St, Philadelphia, Pennsylvania 19104, USA
- Technische Universität, München, Physik-Department E22 Biophysik, James-Franck-Str. 1, 85747 Garching, Germany
- Department of Physics and Astronomy, Vrije Universiteit Amsterdam, De Boelelaan 1081, 1081HV Amsterdam, The Netherlands
Correspondence to: Paul A. Janmey1,2 e-mail: janmey@mail.med.upenn.edu
Correspondence to: Fred C. MacKintosh4 e-mail: fcm@nat.vu.nl
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