Viscoelasticity of the vessel wall: The role of collagen and elastic fibers

The aortic wall contains collagen fibrils, smooth muscle cells, and elastic fibers as the primary load-bearing components. It is well known that the c ollagen fibrils bear loads in the circumferential direction, whereas elasti c fibers provide longitudinal as well as circumferential support. Stiffenin g of the vessel wall is associated with loss of elastic tissue and increase s in the collagen content; however, little is known about the mechanism of vessel wall stiffening with age. The purpose of this review is to attempt t o relate structural changes that occur to the collagen and elastic fibers t o changes in the viscoelastic behavior that are associated with aging. Anal ysis of the viscoelastic mechanical properties of collagen fibrils from ten don, skin, and aortic wall suggest that the collagen fibrils of aortic wall are different than those of other tissues. The elastic spring constant of the collagen fibrils in vessel walls is significantly less than that found in tendon, suggesting that the presence of type III collagen in aortic wall increases the flexibility of the collagen fibrils. Furthermore, it is hypo thesized that changes in the interface between collagen fibrils, elastic fi bers, and smooth muscle during aging and in connective tissue disorders lea ds to changes in the viscoelasticity of the vessel wall.