Marine collagens, both from vertebrates and invertebrates, have attracted many scientists that work in Tissue Engineering in the last decade as they may represent a sustainable and safer source for the development of needed biomaterials. 
Collagen is the major structural component of the whole animal Kingdome and all animals, from sponges to humans, have at least one kind of fibrillar collagen (Type I) and one type of non-fibrillar collagen (type IV). In Nature we can mainly find two subcategories of fibrillar collagens: collagens that are permanently crosslinked and collagens that have labile linkages between fibrils and can rapidly change the nature of the crosslink between the collagen fibrils, becoming much more resistant or more compliant in a short timescale (seconds to minutes). In this latter category, often group under the name “Dynamic Collagenous Tissues”, the most famous example is represented by the Mutable Collagenous Tissues (MCT’s) of echinoderms. It is generally less known that also other Phyla have similar characteristics, including: sponges; cnidarians and molluscs. While traditionally collagens with stable bonds between fibrils are extracted in diluted acetic acidic solution (ASC) or with enzymatic digestion (PSC), collagens of echinoderms and sponges are mostly unaffected by those treatments. Collagen is istead extracted in neutral buffers in the presence of chelating and reducing agents. These extraction methods generally end up in a liquid colloidal suspension of fibrils where the molecules associated with collagen (namely proteoglycans and glycosaminoglycans) are preserved.
Here we present an improved collagen extraction method that ends up directly in a spontaneous hydrogel formation. Collagens hydrogels, extracted from a common marine sponge, have been characterized in the protein profile, rheology and Fourier Transformed InfraRed spectra. A discussion on the sticking features and the possible applications of collagen extracted with this method is here presented.