Strain-induced alignment in collagen gels

TL;DR

This study investigates how mechanical strain induces fiber alignment in collagen gels, revealing that uncrosslinked networks exhibit irreversible alignment while crosslinked ones show reversible alignment, highlighting fundamental non-linear network properties.

Contribution

The paper introduces new analysis tools and an experimental setup to study strain-induced fiber alignment in collagen networks, distinguishing between crosslinked and uncrosslinked behaviors.

Findings

Uncrosslinked collagen networks show irreversible fiber alignment under strain.

Crosslinked networks exhibit reversible fiber alignment, similar to uncrosslinked networks.

Fiber alignment results from the non-linear mechanical properties of fibrous networks.

Abstract

Collagen is the most abundant extracellular-network-forming protein in animal biology and is important in both natural and artificial tissues, where it serves as a material of great mechanical versatility. This versatility arises from its almost unique ability to remodel under applied loads into anisotropic and inhomogeneous structures. To explore the origins of this property, we develop a set of analysis tools and a novel experimental setup that probes the mechanical response of fibrous networks in a geometry that mimics a typical deformation profile imposed by cells in vivo. We observe strong fiber alignment and densification as a function of applied strain for both uncrosslinked and crosslinked collagenous networks. This alignment is found to be irreversibly imprinted in uncrosslinked collagen networks, suggesting a simple mechanism for tissue organization at the microscale. However, crosslinked networks display similar fiber alignment and the same geometrical properties as uncrosslinked gels, but with full reversibility. Plasticity is therefore not required to align fibers. On the contrary, our data show that this effect is part of the fundamental non-linear properties of fibrous biological networks.