  In our work we compare the mechanical properties of the extracted keratin
cytoskeleton of pancreatic carcinoma cells with the mechanical properties of in
vitro assembled keratin 8/18 networks. For this purpose we use microrheology
measurements with embedded tracer beads. This method is a suitable tool,
because the size of the beads compared to the meshsize of the network allows us
to treat the network as a continuum. Observing the beads motion with a
CCD-High-Speed-Camera then leads to the dynamic shear modulus. Our measurements
show lower storage moduli with increasing distance between the rim of the
nucleus and the bead, but no clear tendency for the loss modulus. The same
measurement method applied to in vitro assembled keratin 8/18 networks shows
different characteristics of storage and loss moduli. The storage modulus is
one order of magnitude lower than that of the extracted cytoskeleton and the
loss modulus is higher. We draw conclusions on the network topology of both
keratin network types based on the mechanical behaviour.
