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 invivo
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.