CAREER: Exploring the Recluse Spider's Strong Nanometer-Thin Silk Ribbons

College Of William And Mary, Williamsburg VA

Investigators

Abstract

Non-technical Abstract This CAREER award by the Biomaterials program in the Division of Materials Research to College of William and Mary is to investigate ribbon-like silk fiber of the brown recluse spider with respect to its hierarchical structure, and mechanical and adhesive properties, as well as its ability to form even stronger hybrid graphene-nanocomposite materials. Spider silks have outstanding strength and toughness; at the same time, they are naturally produced in a fully sustainable way, not using petroleum, large amounts of energy, or any toxic materials. As natural materials, they are also interesting for medical applications, such as implants. This combination of properties makes silks highly interesting as high performance materials. In this project, the investigator will study the silk of the brown recluse spider, which has a unique shape. In contrast to the other silk fibers, the filaments of the recluse are not cylindrical, but extremely flat and thin ribbons, resembling miniaturized pieces of sticky tape - ten times narrower and one thousand times thinner than a human hair. Previous studies by this researcher have shown that these ribbons share the outstanding mechanical properties with the best spider silks; at the same time, their unique shape gives rise to interesting new behavior, such as enhanced adhesion, and it allows the application of powerful analytical tools. Therefore, this project is expected to further our understanding of silks and their microstructure in general, and will reveal some of the unique properties of recluse silk in detail, such as their stickiness, and strength. This knowledge is a direct precursor to exploiting this exciting material for future engineering and biomedical applications. This project plans to provide participation and learning experiences for students from high school to graduate levels. Technical Abstract This CAREER award by the Biomaterials program in the Division of Materials Research to College of William and Mary is to investigate ribbon-like silk fiber of the brown recluse spider with respect to its hierarchical structure, and mechanical and adhesive properties, as well as its ability to form even stronger hybrid graphene-nanocomposite materials. Unlike many other synthetic or natural polymers, these silk fibers are freestanding, 50 nm-thin and 5 ìm-wide protein ribbons. Previous studies by this researcher showed that the tensile performance rivals the strongest silks; at the same time, their unique morphology gives rise to novel properties and allows high-resolution structural characterization using atomic force microscopy. The structure of the recluse ribbons is simpler than other silks; a thin silk film with such outstanding strength is a novelty. Due to their thinness, these silk ribbons bend easily, which allows them to maximize the contact area with surfaces or objects they are in contact, enabling stronger van der Waals adhesion. The stickiness may further be enhanced by the nano-papillae, globular nanoscale surface features, and these features have not been observed in any other silks. The recluse ribbons would thus serve as a model system to improve our understanding of silks in general, and as a benchmark for biomedical silk films. The educational plan of this project is to provide research experiences to undergraduates from several disciplines; and special activities are planned to reach out to high school students. The research will be featured in new undergraduate and graduate classes making use of inverted learning techniques and digital technology.