Cross-linking of fibrous collagenous tissues occurs during late-stage wound healing and during aging. The attendant changes in micro-scale kinematics and macro-scale mechanics are not well understood. In this study we used glutaraldehyde as a model cross-linking agent, and in vitro reconstituted collagen gel as a model collagenous tissue. Collagen gels are in vitro assembled hydrated networks of collagen fibrils. Glutaraldehyde is a commonly used cross-linking agent for bioprosthetic tissues and is chemically well-characterized. Glutaraldehyde cross-linking is known to decrease the deformability of arterial valves, but the micro-scale mechanism of its action is not known. In this study, collagen gels with anisotropic fibril orientation were subjected to increasing cross-link density, and the concurrent change in biaxial mechanical properties was monitored. The extent of cross-linking is determined by biochemical analysis. Structural modeling of the biaxial mechanics of a fibrous microstructure was performed for three potential cross-link mechanisms. The trends in the simulated mechanics for increasing cross-link density were compared against that of the experimental data.
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