(398br) Mimicking Nature: Mechanical Properties of Ultrastretchable, Silica-Based Synthetic Spider Webs Fabricated Via 3D Printing

Spider-webs are one of the most fascinating and precisely engineered architectures seen in nature. The structure of a web consists of a spiral supported with spokes, all weaved using elastic silk. Ability of this thin net to capture high velocity objects is not only a way to obtain food for spiders, but also has been adapted into our lives, where similar manmade nets mitigate accidents in fields like construction, sports, and aviation by acting as a barrier. As 3D printing becomes a common and facile approach to pattern traditional as well as novel materials into intricate geometries, designing and mimicking spider webs is starting to attract scientific attention. The wide range of existing inks allows us to print complex 3D structures: from common small household tools to commercial assemblies, such as jet engines or buildings with multiple rooms; however, there is still a need for inks with unique nature-imitating functional properties for structural applications. We have used 3D printing to fabricate synthetic spider webs, with an in-house synthesized polyurethane composite as an ink to mimic spider silk properties.

By reacting polyurethane with i) ethylene glycol, ii) hydroquinone, and iii) fumed silica particles, we have synthesized three types of polymers with varying tensile properties. We have quantified the glass transition temperature and rheological properties of the polymers. Both films and fibers prepared with polyurethane-silica composites were highly stretchable, with an average strain above ~4000 % at break of the fibers. We propose that these tensile properties originate from the covalent and non-covalent 3D crosslink system between the elastic polymer and rigid silica domains. The polyurethane-silica composite was cast into films, wet spun into fibers and used as an ink for 3D printing at room temperature using a customized 3-dimensional pneumatic dispensing robot. We 3D printed grids and spider-webs with increasing number of interconnected junctions, relating mechanical properties to the architecture. This in depth understanding of the structural-functional-property relationship of elastic nets will enable future design of complex structures, requiring advanced functional materials for high tech applications.