Protein composites from silkworm cocoons as versatile biomaterials

Silk is a naturally occurring biopolymer formed into fibers composed primarily of fibroin and sericin proteins. The outstanding mechanical properties of silk fibroin (SF) provides numerous applications for silk based biomaterials. However, the canonical approaches for fabricating silk-based biomaterials typically involve degumming to remove the silk sericin (SS) to avoid adverse biological effects. Meanwhile, sericin has multiple biological functions including outstanding hydrophilicity, promoting cell attachment that are useful to exploit in new materials, inspiring the use of sericin-based biomaterials for biomedical applications. However, compared to fibroin, sericin is not a structural protein, thus sericin-based materials do not provide robust mechanical properties. To address this problem, we report an effective method for fabricating silk fibroin-sericin protein (SS-SF) composites directly from whole cocoons, negating the traditional extraction step to remove the sericin. This approach combines the material features from both fibroin as a structural unit and sericin as a biological functional unit, to achieve advantages regarding processing and materials properties, not only simplifying processing and maintaining the mechanical properties of the fibroin by avoiding degumming, but also endowing these SS-SF composite materials with enhanced hydrophilicity and cell adhesion performance to promote cell growth and proliferation. In addition, these protein composites could be fabricated into a variety of materials formats (e.g. films, sponges, monoliths) to fit different biomedical applications. Statement of significance Canonical approaches for fabricating silk-based materials typically involve degumming to remove sericin, yet sericin has multiple biological properties that are useful for fabricating materials. Here, the concept of fabricating fibroin-sericin protein composites into a broad range of material formats directly from whole cocoons was demonstrated, with a focus on simplifying processing steps and improving biological functions of the materials. The results show that different formats of these new fibroinsericin protein composites can be fabricated (e.g. films, sponges, monoliths) with biological functions to promote cell adhesion, growth and proliferation. These silk composites combining fibroin-sericin protein composite systems open up an interesting field of sericin and fibroin-based materials research. (c) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Automated summary

Silk is a natural biopolymer composed of fibroin and sericin proteins. Traditional methods of fabricating silk-based biomaterials involve degumming to remove sericin, but sericin has beneficial biological properties that can be utilized in biomedical applications. Developing fibroin-sericin protein composites directly from whole cocoons simplifies processing steps and enhances the biological functions of these materials, opening up new possibilities for silk-based research in various formats to promote cell growth and proliferation.