Rheology of reconstituted type I collagen gel in confined compression

Abstract

Collagen gels are used extensively for studying cell-matrix mechanical interactions and for making tissue equivalents, where these interactions lead to bulk deformation of the sparse network of long, highly entangled collagen fibrils and syneresis of the interstitial aqueous solution. We have used the confined compression test in conjunction with a biphasic theory to characterize collagen gel mechanics. A finite element method model based on our biphasic theory was used to analyze the experimental results. The results are qualitatively consistent with a viscoelastic collagen network, an inviscid interstitial solution, and significant frictional drag. Using DASOPT, a differential-algebraic equation solver coupled with an optimizing algorithm, the aggregate modulus for the collagen gel was estimated as 6.32 Pa, its viscosity as 6.6 ϫ 10 4 Pa s, and its interphase drag coefficient as 6.4 ϫ 10 9 Pa s m Ϫ2 in long-time ͑5 h͒ creep. Analysis of short-time ͑2 min͒ constant strain rate tests gave a much higher modulus ͑318.3 Pa͒, indicating processes that generate high resistance at short time but relax too quickly to be significant on a longer time scale. This indication of a relaxation spectrum in compression is consistent with that characterized in shear based on creep and dynamic testing. While Maxwell fluid behavior of the collagen network is exhibited in shear as in compression, the modulus measured in shear was larger. This is hypothesized to be due to microstructural properties of the network. Furthermore, parameter estimates based on the constant strain rate data were used to predict accurately the stress response to sinusoidal strain up to 15% strain, defining the linear viscoelastic limit in compression.

Oriented collagen fibers direct tumor cell intravasation

“…First, the injection of liquid Collagen I into viscous liquid Matrigel led to external forces that constrained the macroscopic shape of the Collagen I fiber network during gelation (31,32). Further, the swelling Matrigel anisotropically squeezed specific Collagen I regions after immersion in the culture medium, leading to further fiber reorientation and reorganization.…”

On a poroviscoelastic model for cell crawling

“…They describe a hydrated collagen network as a two-phase fluid, where the collagen network is an upper-convected Maxwell fluid. In Knapp et al (1997) the model predictions are compared to measurements from a simple experimental set-up and found to be in good agreement.…”

“…Both these models are single phase models. For further justification we appeal to models developed in Knapp et al (1997) and Ohsumi et al (2008) for a similar system. They describe a hydrated collagen network as a two-phase fluid, where the collagen network is an upper-convected Maxwell fluid.…”

An investigation of the influence of extracellular matrix anisotropy and cell–matrix interactions on tissue architecture

“…However, experimental studies suggest that they can be treated as isotropic, upper-convected Maxwell fluids (Barocas et al, 1995;Knapp et al, 1997;Schreiber et al, 2003). In what follows, we treat the gel as a viscous fluid, justifying this simplifying assumption by estimating its Deborah number to be small (the Deborah number is the ratio of the stress relaxation timescale to the experimental timescale).…”