Laser technique unravels spider silk’s mysteries

Ashley N. Rice, ashley.rice@photonics.com

A noninvasive, noncontact laser light scattering technique may be the key to unraveling the secret behind spider silk’s strength.

“Spider silk has a unique combination of mechanical strength and elasticity that make it one of the toughest materials we know,” said professor Jeffery Yarger of Arizona State University’s (ASU) Department of Chemistry and Biochemistry. “This work represents the most complete understanding we have of the underlying mechanical properties of spider silks.”

Although spider silk is an exceptional biological polymer, it is more complex in structure than its kin, collagen (the stuff of skin and bones), scientists say.

A female Nephila calvipes on her web. The web was characterized using Brillouin spectroscopy at Arizona State University to directly and noninvasively determine its mechanical properties. Courtesy of Jeffery Yarger.

Yarger and colleagues are using Brillouin light scattering to examine the silk’s molecular structure. The elastic and mechanical properties of spider silk in situ, obtained by the ASU team, are the first of its kind and could aid in modeling efforts designed to understand the interaction of the mechanical properties and the molecular structure of silk used to generate spider webs.

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

The team recorded an extremely low power laser beam (less than 3.5 mW) as it passed through four types of intact spider webs: Nephila clavipes, A. aurantia, L. Hesperus and P. viridans. Spatial maps detailing the elastic stiffness of each web were derived without deformity or disruption, with findings showing variations among discrete fiber, junctions and glue spots.

The unique silk property supercontraction, one of the most studied aspects of orb-weaving dragline spider silk, also was investigated. This property leads to significant shrinkage in unrestrained dragline fibers, which the scientists’ hypothesis confirms helps spiders adapt to the properties of the silk during the spinning process.

Results of the study could aid in the creation of materials ranging from bulletproof vests to artificial tendons.

“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,” Yarger said.

The findings were reported in Nature Materials (doi: 10.1038/nmat3549).