Viscoelastic studies of extracellular matrix interactions in a model native collagen gel system

We describe an in vitro test of the hypothesis that viscoelastic properties of the collagen fiber network of skin are influenced by interactions between the macromolecular components in the extracellular matrix. Native type I collagen gels were investigated as a mechanical analog for connective tissue. A series of gels were formed under physiological conditions via fibril precipitation in the presence of selected matrix macromolecules, including dermatan sulfate (DS), hyaluronic acid (HA), dermatan sulfate proteoglycan (DSPG), fibronectin (FN) and elastin. Viscoelastic measurements and transmission electron microscopy were performed to explore the relationship between mechanical strength and fibril morphology. The results demonstrate that associative interactions of DSPG and HA with collagen fibrils, as well as variations in collagen fibril size distribution and the amount of elastin, can modify the viscoelastic behavior of the model collagen gels. Addition of DSPG, DS and HA increases both storage and loss moduli, G' and G"; morphological examination shows adhesive binding of these species to the collagen fibrils. At 37 degrees C, elastin increases G' by forming elastic coacervate particles. FN has no effect on the gel viscoelasticity. The observed effects are discussed in terms of current clinical observations on age-related changes in the mechanical properties of skin.