Figure 6.

Model of holothurian dermis. The dermis is modeled as a material with three structural levels. Level 1, collagen fibrils: each fibril is an aggregation of subfibrils (white circles) embedded in a matrix (black filling between subfibrils); the stiffness of the matrix is controlled through tensilin and softenin. Level 2, fibril bundles (fibers): each bundle consists of fibrils linked by crossbridges (black bars) and embedded in a matrix whose stiffness is controlled by the number of crossbridges. Level 3, dermis: the bundles are embedded in a hydrogel of proteoglycans (represented as tadpole-shaped molecules) whose stiffness is controlled by bonds between proteoglycans, bond formation being associated with water exudation; the arcs with a star at each end denote bonds between proteoglycans. (From reference [71], https://doi.org/10.1371/journal.pone.0155673 (accessed on 2 May 2023), under the terms of the CC BY 4.0 license, https://creativecommons.org/licenses/by/4.0, accessed on 2 May 2023).