Nanofibrils: Quest to the Origin of Spider Silk's Strength, Toughness, and Formation

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Nanofibrils: Quest to the Origin of Spider Silk?s Strength, Toughness, and FormationNon-Technical Abstract: Spider silk is an intriguing material that has fascinated researchers and laymen alike. Featuring outstanding strength and toughness, spider silk outperforms some of the best man-made materials. These properties are intimately related to the highly sophisticated structure of silk, revealing different features when studied at increasing magnifications. Nanofibrils have recently been identified to play a key role in this structure; their outstanding properties will thus be at the center of this project and will be studied in terms of their structure, properties, and functions. Several of the most advanced microscopy and spectroscopy techniques will be combined to reveal the internal structure of the nanofibrils, with the ultimate goal of obtaining a complete understanding of silk fibers across all length scales, starting at the molecular level and reaching to the size of the entire silk fiber. One of the goals of this project is to provide the foundations for future efforts to synthesize outstanding materials inspired by spider silk. Because of the critical importance of nanofibrils, the project will study the conditions of their formation, ultimately to enable the fabrication of synthetic fibers made of such nanofibrils. In this pursuit, several graduate and undergraduate students will acquire specialized training in materials testing and characterization, high-resolution imaging, materials manipulation at the nanoscale and computer modeling. The project includes multiple outreach activities to bring this exciting spider silk project to students in elementary, middle, and high schools with the goal of motivating them to pursue careers in STEM disciplines.Technical Abstract: This research project studies a broad range of aspects of silk nanofibrils, which have recently been identified as key structural and functional elements in silk fibers. To fully reveal the hierarchical structure of silk fibers across all length scales, a broad range of imaging techniques will be employed, including atomic force microscopy, scanning electron microscopy, and transmission electron microscopy. These techniques will be complemented by spectroscopic and inverse-space characterization methods, including vibrational spectroscopy, solid-state nuclear magnetic resonance, and X-ray diffraction. Finite element analysis will be employed to develop a coherent model of the mechanical properties of silk fibers, with the ultimate goal of relating the observed macroscopic performance of a silk fiber to its hierarchical structure across the length scales. Because nanofibrils are so critical to the performance of silk fibers, this project will also study their conditions of formation. Molecular self-assembly of silk proteins is a very promising route to bottom-up fabrication of silk nanofibrils and will be employed in this project to determine the most critical parameters of nanofibril formation. The knowledge gained in this project will be critical to future efforts to synthesize outstanding materials inspired by spider silk: the hierarchical structure determined in the project will serve as a template for materials synthesis; the self-assembly mechanisms revealed by the project can be employed to ultimately realize these hierarchical structures starting at the molecular scale. The project includes multiple outreach activities to bring this exciting spider silk project to students in elementary, middle, and high schools with the goal of motivating them to pursue careers in STEM disciplines.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.