Dynamic Mechanical Characterization of a Mutable Collagenous Tissue: Response of Sea Cucumber Dermis to Cell Lysis and Dermal Extracts

ABSTRACT The dermis of the holothurian Cucumaria frondosa is a mutable collagenous tissue (MCT). In this study, the inner and outer regions of the dermis were separated and used to make two different tissue extracts. These extracts were applied to intact pieces of dermis, one invoking a stiff mechanical state and the other invoking a compliant state. The extracts were effective on tissues incubated in artificial sea water (ASW) and in those incubated in Ca2+-chelated ASW. Furthermore, the extracts were effective on both fresh tissues and tissues in which the cells had been lysed by freeze–thawing, indicating that the sites of action are in the extracellular matrix. Dynamic oscillatory shear tests and analyses were used to measure both the dynamic shear stiffness (G*) and the relative damping (tanδ) of the tissue. These two parameters proved to be inversely related to each other (i.e. when G* increased, tanδ decreased). A theoretical viscoelastic model is constructed to interpret the results of these tests. It is concluded that changes in the mechanical state of the tissue involve interactions between elastic elements within the tissue rather than an alteration of its viscous components.