Mechanically tunable collagen scaffolds for tissue engineering applications inspired by sea cucumbers

As the average human lifetime increases, so does the incidence of failing tissues and organs in the elderly. Thus, it becomes essential to develop strategies for regenerating replacement tissues in the lab. However, there are still major challenges to effectively engineer artificial tissues and organs with complex 3D structures – most notably the temporal and spatial regulation of tissue scaffold mechanics. To address this challenge, we take inspiration from a unique biological model – the mutable collagenous tissue (MCT) of sea cucumbers (Bonneel et al., 2023). MCT is a collagen-based tissue that can be stiffened and softened through the addition of effector proteins. We hypothesize that sea cucumber-sourced collagen will enable dynamic modulation of mechanical properties for tissue engineering applications, providing several functional advantages over current mammalian-sourced collagen. In particular, MCT scaffolds will provide the ability to tune local mechanical properties in a controlled manner that is not possible with current natural or synthetic tissue scaffold materials.
Yet, harnessing MCT as a dynamically mechanoresponsive scaffold first requires an in-depth understanding of the molecular and structural mechanisms underlying mechanical mutability. Here, we undertook a comparative compositional and structural investigation of two distantly related sea cucumber species–Holothuria forskali and Cucumaria frondosa. For both species, it is known that the effector protein tensilin can rapidly induce a transformation between the soft and standard (stiffer) mechanical states of the dermis (Bonneel et al., 2023). However, the other effector proteins, including softener, have only been partially purified based on their activity, and their identity and sequence remain unknown. Proteomic analyses coupled to transcriptomics first allowed us to investigate the specific molecular components of the MCT from the dermis of H. forskali. Then, we investigated the mechanical, compositional, and structural differences between H. forskali and C. frondosa dermis using a range of cross-disciplinary techniques including histology, tensile testing, FT-IR spectroscopy, X-ray diffraction and confocal Raman spectroscopy. This multi-length scale approach provides new insights into the similarities and differences between MCT from these two species, furthering our understanding of the mechanisms of tunability in this distinctive mechanically adaptive collagenous tissue.