Microstructure and mechanical behavior of cross-linked biopolymer networks

A random fibre network is an ubiquitous microstructure in many materials, ranging from metallic open cell foams through felts, paper and rubbers to the scaffolds of biopolymer filaments in soft tissue and the cell cytoskeleton. While the mechanical behavior of these materials evidently depends on the constituents, the underlying network microstructure is particularly important at large strains. Numerous rheological experiments have shown that random fibre networks of in vitro reconstituted biopolymer networks exhibit strong nonlinear elastic strain-stiffening accompanied with an increase of the shear modulus up to three orders of magnitude. Several synthetic polymer network systems show a similar phenomenology as biopolymer networks, albeit with a much weaker increase of the modulus up to a factor of ~2.

The strain-stiffening in biopolymer networks is, generally, attributed to the properties of the fibres, the cross-links that mediate the inter-fibre force transmission and the network microstructure. Despite much research in the recent past, the mechanical properties of biopolymer networks still hold many mysteries. The conjecture in this thesis is that they are mostly hidden in the network microstructure. Extensive computer simulations have provided a deep insight in the relationship between microstructure and mechanical properties of biophysical networks. This understanding has provided a unified explanation of stiffening in a wide range of biophysical network materials.