S. DeAndrea, S. Stellwagen
University of North Carolina at Charlotte,
United States
Keywords: spider silk, adhesive, thermal shock, extreme speeds, non-Newtonian
Summary:
Orb-weaving spiders produce up to seven distinct silk types, each with unique characteristics and biomaterial properties. Aggregate silk, or the glue on the spider's web, is a non-solid, modified silk protein used to retain prey. This adhesive contains an internal glycoprotein core that is surrounded by an aqueous outer layer which makes its functionality highly dependent on humidity. Aggregate silk, however, has been shown to resist degradation over long periods of time, is tolerant to thermal changes, and can rehydrate after desiccation - all properties that make it a prime candidate for biomimetic design. Using a custom-built biomaterials testing machine with an integrated force transducer, we probed and stretched glue droplets until failure to determine how these adhesives respond to previously untested speeds. Previous experiments tested aggregate silk at .006962 mm/s due to limited testing capabilities. Our study uses speeds of .85 mm/s, 8.5 mm/s, and 85 mm/s, each representing different speeds that webs may experience in nature through prey capture. We tested glue from Argiope aurantia and Trichonephila clavata, which are species from two major orb-weaver families. The adhesive silk was able to withstand higher forces when tested at faster speeds which supports the hypothesis that aggregate silk behaves as a non-Newtonian material. Furthermore, we tested the glues after exposure to more extreme high and low temperatures than previous studies to gauge their tolerance to adverse environmental conditions. Glue samples were exposed to -20 °C or 60 °C for 24 hours and then tested to determine how extreme heat and cold may degrade the material over time. Determining both the thermal and functional tolerance ranges for this adhesive is useful for determining potential commercial applications and informing biomimetic design.