Elastin dehydration through the liquid and the vapor phase: a comparison of osmotic stress models

The swelling and viscoelastic behaviors of samples of purified arterial elastin were investigated to develop a model for studying the viscoelastic behavior of elastin. Two osmotic stress models were used: the vapor phase model (VPM), in which the stress on the elastin sample was applied through the vapor phase by equilibrating the sample over a saline solution, and the liquid phase model (LPM), in which the stress was applied through the liquid phase by equilibrating the sample in aqueous solutions of large molecular weight polymers. The elastin in the VPM showed a highly varied viscoelastic response, and was slightly stiffer and had a slightly higher damping coefficient than the elastin in the LPM at equivalent nominal relative humidities. We believe the difference in behavior of the elastin in the two models was due to geometric distortions of the elastin that occur during dehydration in the VPM. In the LPM, the spaces between the elastin fibrils are filled with water, and in the VPM these spaces collapse when the water is removed. Removal of only the interfibrillar water deswelled the tissue and increased its stiffness and damping coefficient. Viscoelastic spectra obtained at different levels of osmotic stress in the LPM were reducible to one master curve, indicating that the dominant effect of dehydration is a nonspecific reduction of molecular mobility. We conclude that the LPM is a better model than the VPM for studying the effects of dehydration on the mechanical behavior of elastin.