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Letter
Nature 445, 295-298 (18 January 2007) | doi:10.1038/nature05459; Received 28 March 2006; Accepted 16 November 2006
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Reversible stress softening of actin networks
Ovijit Chaudhuri1,2, Sapun H. Parekh1,2 & Daniel A. Fletcher1
- UC San Francisco /UC Berkeley Joint Graduate Group in Bioengineering and Department of Bioengineering, University of California at Berkeley, Berkeley, California 94720, USA
- These authors contributed equally to this work.
Correspondence to: Daniel A. Fletcher1 Correspondence and requests for materials should be addressed to D.A.F. (Email: fletch@berkeley.edu).
Abstract
The mechanical properties of cells play an essential role in numerous physiological processes. Organized networks of semiflexible actin filaments determine cell stiffness and transmit force during mechanotransduction, cytokinesis, cell motility and other cellular shape changes1, 2, 3. Although numerous actin-binding proteins have been identified that organize networks, the mechanical properties of actin networks with physiological architectures and concentrations have been difficult to measure quantitatively. Studies of mechanical properties in vitro have found that crosslinked networks of actin filaments formed in solution exhibit stress stiffening arising from the entropic elasticity of individual filaments or crosslinkers resisting extension4, 5, 6, 7, 8. Here we report reversible stress-softening behaviour in actin networks reconstituted in vitro that suggests a critical role for filaments resisting compression. Using a modified atomic force microscope to probe dendritic actin networks (like those formed in the lamellipodia of motile cells), we observe stress stiffening followed by a regime of reversible stress softening at higher loads. This softening behaviour can be explained by elastic buckling of individual filaments under compression that avoids catastrophic fracture of the network. The observation of both stress stiffening and softening suggests a complex interplay between entropic and enthalpic elasticity in determining the mechanical properties of actin networks.
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