The glue that coats the silk threads of spider webs is actually its own kind of hydrogel.
If this gel is filled with water, however, how does the spider substance maintain its stickiness in high humidity? Why doesn’t its strength fade, like a band-aid on wet skin?
Saranshu Singla and other fellow graduate students at the University of Akron investigated these questions.
The team’s findings, recently published in the Nature Communications journal, may provide a clue to developing stronger commercial adhesives. Singla spoke with Tech Briefs about ideas for new kinds of spider-inspired coatings.
Tech Briefs: What inspired you to do this work?
Saranshu Singla: The paint peeling off the wall during summer’s high humidity or the band-aid separating from the wet skin is a common occurrence in our everyday lives. This is due to the presence of interfacial water between the adhesive and the surface, which interferes with the adhesive bonds.
In contrast, spiders are able to catch their prey in both dry and humid conditions, using the sticky capture glue present in their webs. It’s puzzling how the spider-capture glue maintains its stickiness in high humidity, where most commercial synthetic adhesives fail. Therefore, we designed a study to understand how spider-capture glue maintains its stickiness at high humidity.
Tech Briefs: What is spider glue, and what is special about its properties?
Singla: A spider coats the capture spiral threads of its web with a uniform coating of the glue, which rapidly pinches off into tiny glue droplets on the underlying thread.
Spider glue is a complex mixture of glycoproteins (a protein with sugar groups) along with a cocktail of hygroscopic (water-attracting) compounds and water. These hygroscopic compounds make the spider glue soft and tacky by absorbing atmospheric water.
You might imagine spider glue as a soft and sticky hydrogel (full of water), which is used by spiders to catch prey in their webs in both dry and humid environment. But if spider glue is a hydrogel, then why is spider glue able to stick in highly humid conditions?
Tech Briefs: Why is it important to do this study?
Singla:We were intrigued by the fact that the water present inside the spider glue does not interfere with the adhesive contact the same way as it does with most synthetic adhesives. Thus, we designed a study to understand how spider glue overcomes the primary obstacle of interfacial water using a combination of interface-sensitive spectroscopy and infrared spectroscopy. To our surprise, we found that the liquid-like water is completely excluded from the contact boundary by the hygroscopic compounds.
Tech Briefs: Given your conclusions, what is now possible?
Singla: This unravels a previously unknown function of hygroscopic compounds in preventing adhesive failure by pulling water away from the contact boundary, which will initiate the future design of synthetic glues for paints, medical bandages, and tissue adhesive applications.
Tech Briefs: What’s next for you regarding the spider-glue research?
Singla: In the future, we would like to use the same methodology to investigate the glue from a different type of spider to investigate if all spiders use a similar approach. Also, we would like to incorporate the findings from our current study to create a unique coating, which will be able to prevent penetration of water to a coating/substrate interface to prevent adhesive failure.
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