Dynamic mechanical characterization of a mutable collagenous tissue: Response of sea cucumber dermis to cell lysis and dermal extracts

The dermis of the holothurian Cucumaria frondosa is a mutable collagenous t issue (MCT), In this study, the inner and outer regions of the dermis were separated and used to make two different tissue extracts. These extracts we re applied to intact pieces of dermis, one invoking a stiff mechanical stat e and the other invoking a compliant state. The extracts were effective on tissues incubated in artificial sea water (ASW) and in those incubated in C a2+-chelated ASW, Furthermore, the extracts were effective on both fresh ti ssues and tissues in which the cells had been lysed by freeze-thawing, indi cating that the sites of action are in the extracellular matrix. Dynamic os cillatory shear tests and analyses were used to measure both the dynamic sh ear stiffness (G*) and the relative damping (tan delta) of the tissue. Thes e two parameters proved to be inversely related to each other (i.e. when G* increased, tan delta decreased), A theoretical viscoelastic model is const ructed to interpret the results of these tests. It is concluded that change s in the mechanical state of the tissue involve interactions between elasti c elements within the tissue rather than an alteration of its viscous compo nents.