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Séminaires MSC
"Matière et Systèmes Complexes"
                      
Lundi 13 juin 2005 à 11h30
Tour 33, couloir 33-43, 2ème étage, salle de réunion

Joseph Käs

(Institut für Experimentelle Physik I, Universität Leipzig)
  Polymers in Cells – A journey from fundamental polymer science to cancer diagnosis and nerve repair

 The physics of biological cells signifies the next fundamental challenge to soft matter physics since it requires to create polymer physics for thermal nonequilibrium (an aspect which is usually only considered in nonlinear dynamics) and to combine cutting edge techniques from nanosciences, nonlinear optics, laser trapping and gene technology.  Since all eukaryotic cells, depend in their internal structure and organization on the cytoskeleton we particularly strive to understand the physics of the cytoskeleton.  Polymeric actin networks provide the rigidity for biological cells.  We discovered that molecular motors can significantly lower the stress relaxation time, effectively fluidizing an actin gel.  This result demonstrates that switch-able nano-sized motors can regulate the strength of polymeric materials.  We have developed an optical stretcher that can serve as a unique tool for studying the viscoelastic properties of dielectric material such as biological cells.  We are now exploring the possibility of using the optical stretcher as a first method for not only detecting single cancer cells by cytoskeletal changes, but also precisely determing the degree of progression of the disease.  Furthermore, the initial and formative factors in nerve regeneration as well as the formation of neuronal circuits in vivo are determined by the speed and the direction that the leading edge of a growing nerve the so-called growth cone adopts.  Unlike to optical tweezers, which would exert a physical pulling force on the entire growth cone, we use a weak optical gradient to bios the actin polymerization-driven growth cone motility.