Andreas Bausch and co-workers, Technische Universitaet Muenchen (TUM), Germany, have used a system that can be controlled with actin filaments as a model for studying changes in elasticity. Actin is a biopolymer that is responsible for muscle contractions in the human body. The crosslinking molecule, fascin, and actin filaments build an interconnected network whose elasticity decreases with age.

The team have shown that the macroscopic changes in the polymer network result from microscopic relaxation processes. Using a combination of rheology, confocal microscopy and space-resolved dynamic light scattering, the team showed that internal tensions build up during the formation of the network. The crosslinked points in the network are not permanent, but open and close at random intervals, resulting in the gradual reduction in tension. Over a period of ten hours, the elasticity dropped to about a fifth of the initial value and then remained stable.

• Slow dynamics and internal stress relaxation in bundled cytoskeletal networks
  O. Lieleg, J. Kayser, G. Brambilla, L. Cipelletti, A. R. Bausch,
  Nat. Mater. 2011, 10, 236–242.
  DOI: 10.1038/NMAT2939