Aortic valve cusp microstructure: the role of elastin.

The aortic valve cusp is a three-layered structure, composed of differing amounts of collagen, elastin, and glycosaminoglycans. Little quantitative information is presently available on the amount, location, orientation, and overall structure of these constituents, particularly of elastin. We developed a technique to isolate aortic valve elastin in a morphologically intact state. Whole leaflets were digested in 0.1 N sodium hydroxide solution at a temperature of 75 degrees C. Both scanning electron microscopy and computerized three-dimensional reconstructions of serial sections showed a well-defined honeycomb or spongelike structure, suggesting that elastin forms a matrix that surrounds and links the collagen fiber bundles. This relationship between collagen and elastin is further supported by the naturally wavy configuration of the valve cusps, permitting elongations of 40%, even though collagen fibrils typically strain to 1% to 2% before fracture. Elastin likely acts to return collagen fibers back to their undeformed state, maintaining rest geometry.