The spatial structure (3D) and mechanical properties of the sponge Spongilla lacustris L. (Porifera: Spongillida) skeleton as a potential tensegral architecture

Complex biological systems often provide ready solutions for contemporary engineering. One such organism might be sponges, primitive, tissueless animals whose evolution over 600 million years has allowed them to become highly specialized. An example of such an organism is the freshwater sponge Spongilla lacustris L., an organism that filters water. This study aimed to investigate the 3D structure of the aforementioned sponge using a broad spectrum of techniques such as Microcomputed Tomography (mu CT), Scanning Electron Microscopy (SEM), Confocal Laser Scanning Microscopy (CLSM), and Light Microscopy. Additionally, these techniques have been used to correlate sponge architecture with mechanical properties using the concept of tensegrity, i.e., the feature of architectural structures that self-stabilize by balancing multidirectional, often opposing, tensile and compressive forces. A more detailed look at the structure of the sponge skeleton reveals that it is based on two elements: rigid siliceous spicules, chitin in in fibres with cementing collagen-type spongin material. The coexistence of these elements in the sponge structure determines the mechanical properties and, consequently, the sponge skeleton's postulated tensegrity. Our observations indicate that the integrity of loose megascleres is realized by sponging material surrounding the bundles of spicules. Our distinction of skeletal elements was determined by the number of spicules in the bundle, the direction of spicule position relative to the main body axis, and the way the elements were connected. The arrangement of the bundles described above has important implications for the mechanical properties of the sponge skeleton and, consequently, for the tensegrity hypothesis.