Facile fabrication of hierarchically structured, stimulus-responsive sea cucumber collagen fibers and films.

Collagen-based materials including fibers, gels, and films are widely used in biomedical applications as well as cosmeceutical applications. Current collagen material formation methods are well developed but use complex methodologies that seldom combine all desirable properties: biocompatibility, mechanical tunability, and eco-friendly fabrication. In this study, inspired by the stiffness-altering abilities of sea cucumbers, collagen is extracted from mutable collagenous tissue (MCT) and a facile method for generating highly oriented, pH tunable, and environmentally friendly collagen based fibrous gels, fibers, and films is developed. Despite a lack of covalent cross-linking, these collagenous materials present desirable properties including a high degree of molecular anisotropy, pH tunable assembly and mechanics, and tensile properties similar to skin. Taking advantage of the slightly acidic environment of human skin, we demonstrate that the pH dependent assembly of MCT collagen (MCTC) can be harnessed for creating mechanically robust films that adhere firmly to the skin's surface. Beyond cosmetic and cosmeceutical applications, this shows the clear potential of MCTC as a bio-sourced and sustainable building block for the simple fabrication of advanced materials relevant for tissue engineering, soft robotics, and more. Statement of Significance: Collagen materials are central to biomedical engineering, cosmetics, and regenerative medicine, but many fabrication methods require complex processing, chemical cross- linking, or environmentally harmful conditions. This work harnesses collagen extracted from sea cucumber mutable collagenous tissue (MCT) as a bio-sourced building block for forming aligned fibers and organized films through a simple, pH-responsive process. Unlike many conventional collagen materials, these materials exhibit mechanical tunability, a high degree of structural organization, and skin-like tensile properties without covalent cross-linking. Their ability to assemble and strengthen under mildly acidic conditions enables formation of films that adhere robustly to human skin, highlighting relevance for cosmeceutical applications. More broadly, this study establishes MCT- based materials as versatile, bio-sourced platforms for advanced biomaterials design.