| dc.description.abstracteng | The shape and mechanical properties of eukaryotic cells are determined by
the cytoskeleton, composed of actin filaments, microtubules and intermediate filaments
(IFs). Among these, IFs are considered to be the main determinants of cell stiffness and
strength. The reason for this is that they can withstand much larger deformations than
the other two filament classes. Previous studies have revealed a rim-and-spoke arrangement
of IFs, suggesting that they are involved not only in themechanical stability of the
cytoplasm but also of the plasma membrane. Therefore, the organization of IFs at the
plasmamembrane and their influence on the mechanical properties of cells under a
variety of strains are of great interest.
To mimic the rim arrangement at the plasma membrane under strain, the aim of this
work was the development of an in vitro model system, with focus on the membranebound
vimentin intermediate filaments (VIFs) that allows for uniaxial stretching. To
investigate the rim arrangement, an elastic solid support, namely polydimethylsiloxane
(PDMS), was used to enable lateral stretching of the composite system due to its molecular
flexibility. The hydrophobic PDMS with embedded fluorescent beads was oxidized
to render the surface hydrophilic, and by spreading small unilamellar vesicles (SUVs), a
lipid bilayer was formed. The assembled VIFs coupled to ATTO647N and biotin were
linked to the biotin-decorated lipid bilayer via a neutravidin linker. A lipid reservoir in
the formof SUVs was added to provide the system with excess lipid material. Stretching
of this composite system was achieved by a uniaxial motor-driven stretching device.
Performing stretching of individual membrane-bound VIFs revealed mechanical and
entropic stretching. The former means that elongation of the filament’s contour length
upon stretching occurs, while for the latter pulling out the thermal fluctuations is
observed. If the strain rate and pinning point density were increased, mechanical
stretching rather than entropic stretching was increasingly observed. Additionally, the
underlying lipid bilayer contributed to the reorientation of VIFs by diffusive reorganization
or affected the strain transmission due to sliding and rupturing. The found
properties of single membrane-bound VIFs might contribute to the mechanical response
of membrane-bound VIF networks. Even though filaments in the networks
mainly responded with entropic stretching, so far, there has been no access if mechanical
stretching occurs or not. However, it can be speculated that the applied strains
might be too low to observe mechanical stretching. In summary, an artificial model
system was established that opens up a pathway to study the structural and mechanical
properties of cytoskeletal components under strain in order to imitate the cell cortex in
nature. | de |