Negative normal stress in semiflexible biopolymer gels

Paul A. Janmey, Margaret E. McCormick, Sebastian Rammensee, Jennifer L. Leight, Penelope C. Georges, Fred C. MacKintosh

Research output: Contribution to journalArticlepeer-review

321 Scopus citations


When subject to stress or external loads, most materials resist deformation. Any stable material, for instance, resists compressioneven 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 stress. 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 torsion. 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 gels.

Original languageEnglish (US)
Pages (from-to)48-51
Number of pages4
JournalNature Materials
Issue number1
StatePublished - Jan 10 2007
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • General Chemistry
  • General Materials Science
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering


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