Biopolymers such as actin, microtubules, fibrin and collagen, are ubiquitous in Nature, and form complex networks of connected filaments or bundles. The unusual mechanical properties of these networks find their origin in a non-trivial interplay between the mechanics of their individual components and the geometric properties of the network. In this thesis, we shed light on this multiscale interplay by focusing on the case of collagen type I, a major protein of the extracellular matrix and an important component of tissue engineering materials.

We begin by presenting some experimental results on the unusual bulk properties of in vitro reconstituted collagen networks. From there, we proceed to report experimental measurements on the mechanical properties of individual collagen fibrils. We then explore how these individual fibril properties affect the bulk mechanical behavior of networks by numerically simulating the deformation of collagen gels. Using a three-dimensional finite element Timoshenko beam model, we explain some of the bulk properties measured previously and predict trends in the small-strain and high-strain mechanical properties of the network. Finally, we illustrate the potential impact of our results by describing an experimental and analytical framework for high-resolution measurements of cell-induced mechanical forces in a three-dimensional collagen matrix.