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BIOPOLYMER NETWORKS AND CELLULAR MECHANOSENSING. P.A. Janmey, P. C. Georges, O. Wagner, T. Yeung. Institute for Medicine and Engineering, University of Pennsylvania, Philadelphia 19104 PA.

   Cells and tissues are mechanical as well as biochemical machines, and cellular response to mechanical cues can have as large an influence on structure and function as chemical signals.  The mechanical properties of soft tissue are determined by networks of semiflexible polymers such as those forming the cytoskeleton, which has viscoelastic properties that differ in important ways from the viscoelasticity of common synthetic materials.  Two such features are the high resistance to deformation achieved by a remarkably low volume fraction of  protein, and the increase in stiffness that occurs when the cytoskeletal network is deformed.  The actin filaments, microtubules and intermediate filaments that comprise the cytoskeleton of most cell types are linear polymers with some important similarities but also some fundamental differences.  The stiffness of the individual polymer types is vastly different, with persistence lengths ranging from 1 mm for the 24 nm diameter microtubules to a few 100 nm for the 12-14 nm diameter intermediate filaments.    As a result, viscoelastic features like the strain-dependent shear modulus and the rates of filament movement within networks are also highly variable for these polymers.  However, underlying the unique molecular features of each polymer type are shared mechanical properties that suggest  common principles to account for the elasticity of these materials.   Recent data from rheologic, optical, and scanning force microscopy measurements demonstrate how these different polymers can be combined to produce composite networks that have properties not achievable by conventional materials.

(Supported by NIH GM56707 and HL64388)