Rheology of marine sponges reveals anisotropic mechanics and tuned dynamics

Abstract

Sponges are animals that inhabit many aquatic environments while filtering small particles and ejecting metabolic wastes. They are composed of cells in a bulk extracellular matrix, often with an embedded scaffolding of stiff, siliceous spicules. We hypothesize that the mechanical response of this heterogeneous tissue to hydrodynamic flow influences cell proliferation in a manner that generates the body of a sponge. Towards a more complete picture of the emergence of sponge morphology, we dissected a set of species and subjected discs of living tissue to physiological shear and uniaxial deformations on a rheometer. Various species exhibited rheological properties such as anisotropic elasticity, shear softening and compression stiffening, negative normal stress, and non-monotonic dissipation as a function of both shear strain and frequency. Erect sponges possessed aligned, spicule-reinforced fibres which endowed three times greater stiffness axially compared with orthogonally. By contrast, tissue taken from shorter sponges was more isotropic but time-dependent, suggesting higher flow sensitivity in these compared with erect forms. We explore ecological and physiological implications of our results and speculate about flow-induced mechanical signalling in sponge cells.

The rise of mechanical metamaterials: Auxetic constructs for skin wound healing

“…Even there are some biological tissues that have also been shown to develop auxetic behavior, as it has been reported in cow teat, 8 cat, 7 pig, 9,41 and salamander 42 skins, arteries, 43,44 tendons, 45 cancellous bone, 46 embryonic epithelia, 47 cornea, 48 and more recently, in marine sponges. 49 These biological tissues develop the auxetic behavior mainly because of the structural organization and crosslinking of their ECM fibers, demonstrating the importance of ECM structure in the mechanical behavior of the tissue, and also leading to the idea of using auxetic scaffolds to mimic the mechanical properties of the ECM in order to provide better support for the implanted cells. Left panels: schematic diagram comparing conventional and auxetic material behaviors.…”

“…Even there are some biological tissues that have also been shown to develop auxetic behavior, as it has been reported in cow teat, 8 cat, 7 pig, 9 , 41 and salamander 42 skins, arteries, 43 , 44 tendons, 45 cancellous bone, 46 embryonic epithelia, 47 cornea, 48 and more recently, in marine sponges. 49 …”