ASU scientists unravel the mysteries of spider silk


January 27, 2013

Scientists at ASU are celebrating their recent success on the path to understanding what makes the fiber that spiders spin – weight for weight – at least five times as strong as piano wire. They have found a way to obtain a wide variety of elastic properties of the silk of several intact spiders’ webs using a sophisticated but non-invasive laser light scattering technique.

“Spider silk has a unique combination of mechanical strength and elasticity that make it one of the toughest materials we know,” said Jeffery Yarger, a professor in ASU’s Department of Chemistry and Biochemistry and lead researcher of the study. “This work represents the most complete understanding we have of the underlying mechanical properties of spider silks.” Female Nephila clavipes Download Full Image

Spider silk is an exceptional biological polymer, related to collagen (the stuff of skin and bones) but much more complex in its structure. The ASU team of chemists is studying its molecular structure in an effort to produce materials ranging from bulletproof vests to artificial tendons.

The extensive array of elastic and mechanical properties of spider silks in situ, obtained by the ASU team, is the first of its kind and will greatly facilitate future modeling efforts aimed at understanding the interplay of the mechanical properties and the molecular structure of silk used to produce spider webs.

The team published their results in today’s advanced online issue of Nature materials and their paper is titled “Non-invasive determination of the complete elastic moduli of spider silks.”

“This information should help provide a blueprint for structural engineering of an abundant array of bio-inspired materials, such as precise materials engineering of synthetic fibers to create stronger, stretchier and more elastic materials,” explained Yarger.

Other members of Yarger’s team, in ASU’s College of Liberal Arts and Sciences, included Kristie Koski, at the time a postdoctoral researcher and currently a postdoctoral fellow at Stanford University, and ASU undergraduate students Paul Akhenblit and Keri McKiernan.

The Brillouin light scattering technique used an extremely low power laser, less than 3.5 milliwatts, which is significantly less than the average laser pointer. Recording what happened to this laser beam as it passed through the intact spider webs enabled the researchers to spatially map the elastic stiffnesses of each web without deforming or disrupting it. This non-invasive, non-contact measurement produced findings showing variations among discrete fibers, junctions and glue spots.

Four different types of spider webs were studied. They included Nephila clavipes (pictured), A. aurantia (“gilded silver face”-common to the contiguous United States), L. Hesperus, the western black widow and P. viridans, the green lynx spider, the only spider included that does not build a web for catching prey but has major silk elastic properties similar to those of the other species studied.

The group also investigated one of the most studied aspects of orb-weaving dragline spider silk, namely supercontraction, a property unique to silk. Spider silk takes up water when exposed to high humidity. Absorbed water leads to shrinkage in an unrestrained fiber up to 50 percent shrinkage with 100 percent humidity in N. clavipes silk.

Their results are consistent with the hypothesis that supercontraction helps the spider tailor the properties of the silk during spinning. This type of behavior, specifically adjusting mechanical properties by simply adjusting water content, is inspirational from a bio-inspired mechanical structure perspective.

“This study is unique in that we can extract all the elastic properties of spider silk that cannot and have not been measured with conventional testing,” concluded Yarger.

The Department of Defense and the National Science Foundation supported this research.

Media source:
Jeffery Yarger, jyarger@gmail.com
480-965-0673

Jenny Green

Clinical associate professor, School of Molecular Sciences

480-965-1430

Professor receives top science education honor


January 28, 2013

ASU's Dale Baker has been named recipient of the most prestigious award in the field of science education from the National Association for Research in Science Teaching. A professor in the Mary Lou Fulton Teachers College, Baker has contributed more than 30 years of research examining equity issues in science, science teacher professional development and engineering education.

Baker will travel to Puerto Rico in April to accept the 2013 Distinguished Contributions to Science Education through Research Award from the 85-year-old global organization. Download Full Image

“Professor Baker is an exemplar of a College of Education faculty whose impact on schools is not only through her research but also through teaching future teachers and mentoring of future researchers,” said Mari Koerner, dean of Teachers College.

Baker’s inspiration to study barriers to girls and women in science began with her own frustrations in the late 1960s. Typically, she was the only female in her university science classes and had to endure many negative experiences as a result.

“I had a geology lab in college where I was one of two women, and the other one dropped the class,” Baker said. “None of the males would let me join their lab group, so I had to do the lab alone. Even the instructor told me maybe I should quit coming to class and get married instead.”

Baker persisted, however, and pursued a career in science education. Teaching science to K-12 students, she observed that her students “loved science” when they were taught differently – using hands-on activities to help them learn. That realization sent her back to graduate school to pursue advanced degrees and research creative ways to engage students in learning science in the classroom.

In 1995 Baker co-authored a study, “Letting Girls Speak Out About Science,” which looked at the factors influencing girls to choose science. The researchers interviewed 40 girls in grades two, five, eight and 11, and focused on their feelings about science, science careers, support from friends and parents and how science is taught. It was a watershed moment in how people looked at the issue, Baker explained.

“Up to that point, studies about women in science had always compared women to men,” she said. “It was like the song in ‘My Fair Lady’: Why can’t a woman be more like a man? The data was confusing. So I decided to just look at what the girls had to say.”

One of the questions in Baker’s study asked each girl to respond as if she were a boy to see if she would change her answer. Instead, the girls remained strong in their belief that women can and should do science, she said.

“The reasons they liked science were different than those for boys,” Baker said. “The girls had strong, positive emotional experiences that drew them to science. For example, one talked about how when she was little her grandfather wrapped her in a blanket and they sat out on the deck looking at stars and naming constellations. Another said her mother would be proud if she studied science. They weren’t boys.”

The study was selected by the Journal of Research in Science Teaching, the lead journal in science education, for its issue featuring the most influential research in the past 40 years of the publication. Baker has been co-editor of JRST and also serves on editorial boards of the International Journal of Learning Technology and the Journal of Engineering Education.

More recently, Baker has expanded her research on equity issues in science education to include students with physical disabilities. She is investigating the current state of assistive technology used in Arizona’s high school science classrooms for students with physical disabilities (visual, hearing and orthopedic disability) and determining future needs. The data will be used to help plan professional development programs for both pre-service and in-service teachers, she explained.

“This is a new frontier,” Baker said. “As with women, people with physical disabilities can make a new and different contribution to science based on their perspective. They can make wonderful discoveries based on how they see the world because they ask different questions.”

Championing equity in science education also has meant encouraging the research community to recognize its value, Baker said. In the 1980s, Baker and several female colleagues first approached the National Association for Research in Science Teaching about adding a research strand that would focus on equity issues.

“We actually got push back,” she said. “But over time they added a special interest group and then a strand with a focus on women. Then that was expanded to include equity writ large in science with a strand devoted entirely to cultural, social and gender issues.”

Speaking about the association, Baker said she is honored and overwhelmed to be recognized by her colleagues.

“This organization has been my professional home,” she said. “It’s where I learned to be a professor. For me, this award confirms that I was able to make a contribution that made a difference.”