As fibers go, there’s never been anything quite like spider silk. Stretch it. Bend it. Soak it. Dry it out. Spider silk holds up. It is five times stronger than steel and can expand nearly a third greater than its original length and snap right back like new. Ounce-for-ounce spider silk is even stronger than Kevlar, the man-made fiber used in bulletproof vests.
It would be understandable to think that science knows all there is to know about the remarkable physics of spider silk, but the truth is far from that. Now, using a long-known-but-underutilized spectroscopy technique, a Stanford researcher has shed new light on the mysteries of spider silk.
The complete elastic response of spider silk is described by five elastic constants that define how the web reacts to any possible combination of forces—pulling, twisting or shearing in any direction. All five have never been measured in a pristine spider web. At best, earlier studies have measured one or two of the five constants at a time and, even at that, only in isolated sections of a web. Structurally speaking, the old techniques are the equivalent of testing individual steel beams and cables and trying to extrapolate conclusions about the strength of a bridge.
Looking ahead, Koski believes that understanding the complete properties of a spider web exactly as it exists in nature is key to the engineering of new “bio-inspired” materials that not only mimic, but also improve upon nature.
The research was made possible by the use of a century-old-yet-overlooked measurement technique known as Brillouin spectroscopy. The technique shines laser light on the spider silks. The light produces sound waves in the silks, which, in turn, reflect some light back to the spectrometer. The researchers call the reflection “scattering.”
The spectrometer measures small variations in the scattered light to ascertain the underlying tension of the silk being measured. The power of Brillouin scattering rests in the gentle way it gathers data enabling in situ measurements on spider webs, including mechanical properties at precise spots on the web such as silk intersections and glue spots.
Essentially, Koski and cohort have developed a non-invasive, non-destructive technique to measure the elasticity not just of individual strands of spider silk or even a few interconnected strands, as had those earlier studies, but of an entire intact spider web. Such exhaustive information was previously unobtainable with traditional stress–strain tests, which have to grip single strands or, at most, a few strands between two clamps to stretch them till they break.
The result is that Koski and collaborators are the first to quantify the complete linear elastic response of spider webs, testing for subtle variations in tension among discrete fibers, junctions, and glue spots for every type of deformation possible. It is a remarkable picture of the behavior of one of nature’s most intriguing structures.
This story is reprinted from material from Standford University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.