Glassy Dynamics in Composite Biopolymer Networks*

The cytoskeleton is a highly interconnected meshwork of strongly coupled subsystems providing mechanical stability as well as dynamic functions to cells. To uncover central biophysical principles, it is essential to investigate not only one distinct functional subsystem but rather their interplay as composite biopolymeric structures.
Here, these effects caused by composite structures will be especially addressed with the two key elements of the cytoskeleton actin and vimentin IF. In contrast to previous studies, entangled conformations of these reconstituted composite networks can be described by a superposition of two non-interacting scaffolds. Key elements are the ability to compare different compositions with comparable architectural features as well as to identify polymer-specific interactions, which are typically ignored in most established models. We have experimentally identified inter-filament interactions as a key factor that can overwrite scaling predictions of the classical semiflexible polymer physics by comparing results of networks of actin, vimentin IF, keratin IF and synthetic double-crossover DNA nanotubes.
Acquired results of the linear and non-linear bulk mechanics are captured in the frame of an inelastic glassy wormlike chain model allowing to address the diversity of the polymer types based on their specific interactions, which lead to differing relaxation behaviors for the different polymer types. Accounting for this molecular diversity, the composite effects can be expressed as a superposition of the non-interacting scaffolds.