Rheology of Intermediate Filament Solutions
Introduction
Cells interact mechanically
with their environment through their cytoskeleton, a network consisting largely of filamentous protein
polymers. Reconstituted solutions and networks of these biopolymers have rich
rheological and elastic properties that arise from their semi-flexibility, with
thermal persistence lengths comparable to their contour length. While the
viscoelastic properties of reconstituted models of other cytoskeletal
filaments, most notably F-actin, have been widely studied in vitro, relatively little is known about the network
properties of intermediate filaments (IF). Such knowledge is urgently needed
for understanding how disease-causing inherited mutations in human IF proteins
yield an increase in cell fragility in response to mechanical stresses.
We study both the vimentin and neurofilament networks in vitro by using the multiple particle tracking technique and the conventional rheometry.
Current Projects
1. Previously, we have used
the multiparticle video tracking to observe the thermal motion of micron-sized
colloidal particles embedded in F-actin networks. We found that one-point microrheology
probes filament entanglements resulting in a frequency-independent elastic
modulus; while two-point microrheology probes longitudinal fluctuations of the
filaments resulting in the increase of the elastic modulus. We are using the same method to examine
the dynamics of probe particles in IF networks.
2. We are also exploring the
rheology of IF networks by using the conventional rheometry. For semiflexible F-action networks, individual
filaments are sterically hindered due to the presence of other filaments at the
entanglement length; while for flexible polymers, the steric length is the mesh
size. Both theoretical prediction and experimental data show that the plateau
elasticity due to entanglements scales 
for semiflexible
polymers and 
for flexible
polymers. It has been measured that for entangled vimentin networks 
; moreover, entangled vimentin networks also strain stiffens
under large shear deformation. We are interested in understanding the microscopic
mechanism underlying the plateau elasticity and elastic stiffness of IF
networks.
3. We
would also like to use the confocal microscopy to study the mechanical
properties of both single IF filaments and IF networks.
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lin6@fas.harvard.edu
Department of Physics
Mckay Laboratory, 9 Oxford Street
Cambridge, MA 01238