Spider Glue Investigation Yields Smart Materials Insight
There are three types of people in the world: those who carefully transport insects and arachnids out of the building on sheets of paper, releasing them into the wild to roam free, bite innocent people, and reproduce; those who whip off their hard-soled shoes and gleefully smash anything with an exoskeleton that happens to wander within range; and those for whom the thought of a particularly nasty bug is enough to inspire a scream-enhanced instinctive high-speed run headlong into another room.
I belong to the last category, and thus it is with great trepidation and reluctance that I write about a new body of research out of the University of Akron that examines a pair of spider glues with useful properties.
I’ve read about work people are doing with spider silk threads (the silk tends to be amazingly strong – much stronger than kevlar, for instance, which is the material Superman would have adopted as his benchmark had it been more prevalent back in the day). But until recently I hadn’t stopped to think about what makes spiderwebs such a menace to society and to gnats, namely: they are sticky.
Image courtesy socypath.com
So as it turns out, to my abject horror, there are at least two general types of web-weaving spiders and they use the same set of glands to produce two different types of sticky silk-coating glue.
The first type, orb-weaving spiders, have been around pretty much since the dawn of time, and they produce something called viscid glue, a “glue that acts like a viscoelastic solid. Highly humidity-sensitive, this glue expands in magnitude and demonstrates a monotonous increase in elasticity under increased humidity. The glue also displays a decrease in surface adhesion that results in optimal adhesion at intermediate humidity” (physorg.com). Viscid glue can become stickier or less sticky depending on the humidity level.
The other type of spider, your garden variety cobweb-weaving spider, is a direct descendant of the orb-weavers but produces gumfoot glue, an adhesive material that differs in structure, properties, and response to humidity. Gumfoot glue “acts as a viscoelastic liquid that is resistant to changes in humidity, consequently maintaining constant elasticity and adhesion” (physorg.com). So even when these spiders live in New Orleans or Hotlanta, the glue they produce maintains a consistent level of stickiness.
To figure out how glue from the two types of spiders differed, the research team took individual drops of glue and stretched them at different humidity levels. Observing that viscid glue behaved like a viscoelastic solid and that the gumfoot glue behaved like a viscoelastic liquid, the researchers designed a polymer model of the glue droplets to understand the mechanisms at work behind the responses.
Image courtesy coolphotoideas.com
Understanding the behavior patterns of natural biomaterials, such as spider glue, provides us with insight we can use to develop smart materials and devices that may undergo changes in dimension, properties, and function in response to changes in the environment. Investigating changes wrought by evolution provides us with a means of advancing biomimetic research (research that seeks to understand and mimic nature, Leonardo DaVinci-style). This line of thinking could lead to new adhesives with applications in buildings in humid environments, among other things – and that is why I braved a “spider” keyword Google search in order to illustrate this post.
I have filed this adhesive under WOOD and WATER, for reasons known only to myself.
“Spider Silk Glue Inspires Next-Generation Technology.” Physorg.com 7/22/11. Accessed 7/22/11. URL.
Vasav Sahni, Todd A. Blackledge & Ali Dhinojwala. “Changes in the Adhesive Properties of Spider Aggregate Glue During the Evolution of Cobwebs.” Scientific Reports 7/21/11. Accessed 7/22/11. URL.