Asymmetry of tensile vs. compressive elasticity and permeability contributes to the regulation of exchanges in collagen gels

TL;DR

This study reveals that collagen gels exhibit asymmetric mechanical and permeability responses under tension and compression, affecting fluid exchange and potentially influencing drug transport in tissues.

Contribution

It demonstrates the asymmetric elasticity and permeability of collagen gels under different stresses and links these properties to tissue fluid exchange regulation.

Findings

Permeability decreases under compression in collagen gels.

Strain-stiffening is enhanced under compression.

Asymmetry influences fluid accumulation and transport in tissues.

Abstract

The Starling principle describes exchanges in tissues based on the balance of hydrostatic and osmotic flows. This balance neglects the coupling between mechanics and hydrodynamics, a questionable assumption in strained elastic tissues due to intravascular pressure. Here, we measure the elasticity and permeability of collagen gels under tensile and compressive stress via the comparison of the temporal evolution of pressure in an air cavity sealed at the outlet of a collagen slab with an analytical kinetic model. We observe a drop in the permeability and enhanced strain-stiffening of native collagen gels under compression, both effects being essentially lost after chemical cross-linking. Further, we prove that this asymmetric response accounts for the accumulation of compressive stress upon sinusoidal fluid injection, which modulates the material's permeability. Our results thus show that the properties of collagen gels regulate molecular exchanges and could help understand drug transport in tissues.