Sea urchin wastes valorization: production of innovative composite biomaterials for tissue regeneration

Edible sea urchins are well known worldwide as food delicacies however their gonads are the only eatable part, while all the rest (about the 70-90% of total mass) is discarded as waste. Nonetheless we recently showed that the latter can still be valorized and recycled towards high added-value products, in line with a circular economy approach. Particularly, we previously demonstrated that these waste can be a source of valuable molecules, such as 1) fibrillar and GAG-rich collagen, used to produce innovative and biomimetic biomaterials for skin regeneration (Benedetto et al., 2014; Ferrario et al., 2020) and 2) antioxidant pigments (spinochromes) with a high free-radical scavenging activity (Marzorati et al., 2021). As a step forward, in this work we attempted to combine both sea urchin collagen and spinochromes to develop a novel composite and second-level biomaterial, with both biomimetic and bioactive features. Native collagen was obtained from a well known mutable collagenous tissue, the peristomial membrane, while spinochromes were extracted from the remaining waste (test, spines, soft tissues residues). The obtained composite biomaterials were characterized in terms of morphology, degradation kinetics, release kinetics of the spinochromes and antioxidant activity. SEM analyses indicate that biomaterials are morphologically similar to the simple collagen-based counterpart (as well to native connective tissues), with homogeneous fibrils organization pattern in the absence of undesired aggregates. Porosity was confirmed to be ideal for cells infiltration, settlement and growth. Furthermore, UPLC and ABTS assay indicate that antioxidants remain adsorbed onto the collagenous matrix, without any significant release. Additionally, degradation kinetics in both physiological and enzymatic (collagenase) conditions showed an improvement of the stability of the antioxidants/collagen composites, in comparison to simple collagen-based biomaterial. In addition, the degradation kinetics resulted similar to a commercial bovine membrane used as control (Integra®) in physiological conditions. Subsequently, the antioxidant activity of composite biomaterials was evaluated using ABTS assay directly on the solid composite materials. The results confirmed that the antioxidant activity was maintained on the biomaterial, even after freeze-drying even without antioxidants release in solution. Overall, these data indicate that sea urchin wastes can be profitably exploited to obtain valuable molecules and develop innovative biomimetic and bioactive biomaterial, potentially effective in the promotion of tissue regeneration. As a future perspective, 3D bioprinting technology and sea urchin-derived bioink is currently under development to produce collagen-based bioactive biomaterials with enhanced mechanical properties and tuneable morphologies.