Unusual swelling of elastin

The swelling behavior of the elastin network has been investigated by comparing the linear expansion of samples of purified elastin with the volume expansion of the network, calculated on the basis of composition. Elastin sample dimensions and sample masses were measured under three conditions in which volume changes: thermal expansion at fixed water contents, deswelling due to dehydration, and swelling to greater than normal levels due to the swelling agent, sodium dodecyl sulfate. Isotropic network swelling usually changes length in proportion to the cube root of network volume, but length was found to be directly proportional to volume, showing a greater increase in length than expected. This unusual swelling behavior is attributed to an unusual elastin structure at the subfiber level, but there is insufficient detail on elastin's molecular organization to identify a mechanism to explain how it occurs. Assuming the network swells homogeneously, we describe two models that correctly predict swelling behavior, but these models imply a significant deviation from the structure generally assumed for an elastomeric polymer network of kinetically free molecular chains. Assuming that the network swells heterogeneously removes part of the difficulty with the models, but the observed direct proportionality between length and network volume remains to be explained.