Along Came a Spider


Prof. Xinwei Wang, an associate professor of mechanical engineering at Iowa State University, had college training in the areas of thermal science and energy engineering—but he never thought his most valuable training might come from a spider.

“During my study at Purdue University for my Ph.D., I learned a lot about molecular dynamics and experimental study of thermal transport at extremely small scales, from micrometers down to nanometers,” he says. “In over 10 years, the research in my laboratory has been focused on developing various advanced technologies to characterize the thermal transport in micro/nanoscale materials, and probing temperature, and thermal fields down to atomic scale.”

His studies had him asking how much stretching could affect the thermal conductivity of materials, especially, he says, organic and biomaterials—and here is where his eight-legged friends come in. “Since spider silk features extraordinary mechanical properties, this material came to our mind as the first choice when we decided to explore this thermal science area,” he says.

Wang also says that spider silk previously received attention for its mechanical properties and how to take advantage of them in engineering applications, but there wasn’t any research on the thermal transport. It was partly due to the challenge in studying this—the fibers are minute, sometimes measured in nanometers when it comes to thickness—that helped spur him on. “High-thermal conductivity biomaterials have broader application potential, including as supporting materials for flexible electronics, biocompatible structure for health sensors, and ultra-thermal performance clothes,” he says.

Xinwei Wang, Guoqing Liu and Xiaopeng Huang, left to right, show the instruments they used to study the thermal conductivity of spider silk. Photo: Bob Elbert /

With the National Science Foundation and Army Research Office partly backing him, it was rough at the start, with the first batch of spiders dying before any useful silk could be procured. The second batch was fed better, but still didn’t survive well. Finally, they were able to get the survival needed to collect proper data. His assistant, Xiaopeng Huang, played a key role in designing and conducting experiments, along with collecting samples. Guoqing Liu also assisted in multiple areas, including doing the experiment on silkworm silks to provide a comparison study.

What they found was that spider silk was a better heat conductor than even silicon or iron. In addition, stretching the silk will increase conductivity, allowing potential improvements in everything from parts for electronics to the aforementioned clothing.

“Besides its high thermal conductivity, it is very interesting to see that silk’s thermal transport properties can change a lot by stretching or by absorbing water,” he says. “This points out very unique ways to investigate how the secondary protein structure will change under external stimulation.”

Maybe the most remarkable part of their results is that Wang says this is the highest rate of heat conduction ever for an organic material—even 1,000 times better than woven silkworm silk.

At present, Wang and his team think the beta-sheet crystal and the aligned structure are vital in explaining the observed high thermal conductivity and stretching. “We observed great sample-to-sample variation that could be induced by the age of spiders, their health condition, the food they are fed with, and other unknown factors,” he says. “All these place great challenges to maintain the consistency of experiment. On the good side, all these point out new ways in protein structure control and thermal transport capacity manipulation.”

Eric Butterman is an independent writer.

Since spider silk features extraordinary mechanical properties, this material came to our mind as the first choice when we decided to explore this thermal science area.

Prof. Xinwei Wang, Iowa State University


February 2013

by Eric Butterman,