The inset in the upper right corner of this photo of a typical orb web is an enlarged image of gluey spiral thread, which is key in spider prey-capture. |
Water affects orb spider web glue differently than cobweb
glue. Orb web glue reacts to humidity, but cobweb glue resists it. These
findings by a University
of Akron research team
inspire the development of new materials according to how they respond to
stimuli.
This newly released research by Vasav Sahni, a UA polymer
science graduate student; Todd Blackledge, the Leuchtag Endowed Chair and
associate professor of biology and integrated bioscience; and Ali Dhinojwala,
UA Department of Polymer Science chair and H. A. Morton Professor of Polymer
Science, is published in Scientific
Reports.
Humidity triggers
adaptability
The research shows that the sticky glue that coats the silk threads
orb-weaving spiders spin has a different structure, property makeup, and response
to humidity than glues produced by their evolutionary descendants,
cobweb-weaving spiders. The cobweb spider’s gumfoot glue acts as a viscoelastic
liquid that is resistant to changes in humidity, consequently maintaining
constant elasticity and adhesion.
Orb weavers, on the other hand, produce 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.
“We suggest that observed differences are due to
different ‘tackifiers’ used in these systems,” says Sahni. “These
results will inspire future efforts in fabricating stimuli-resistant and
stimuli-sensitive materials.”
Evolutionary changes
advance science
Behaviors of natural biomaterials, such as spider glue responses to
humidity, provide templates for developing smart materials and devices that
change dimension, property makeup, and function in response to external
stimuli, says Vasav. He adds that evolutionary changes provide powerful tools
to advance biomimetic research toward understanding key elements that control
biomaterials’ environmental responsiveness or resistance to stimuli.
The researchers probed individual glue droplets to reach
their findings. They explain in their paper that “both orb web and cobweb
spiders depend on viscid glue droplets for their silk to adhere to insect prey.
Both types of spiders use the same sets of glands to produce the
adhesive.” However, similarities between the two, for the most part, end
there.
The opposite reactions of the two bioadhesives to humidity
are as dramatic as the complexity of processes contributing to these phenomena,
the scientists explain in their research. Consequently, the researchers
designed a polymer model of the glue droplet, dissolved in water, to simplify
and better understand the underlying mechanisms that cause the orb web spiders’
silk adhesive to react to humidity.
Reactions of spider glue, pine cones, bird feathers, and
several other natural materials to different stimuli provide scientists
inspiration for developing next-generation materials based on biomimetic
research, or research that mimics nature.
