When you explore haunted houses or search for sacred artifacts in ancient temples, the cobwebs that you brush out of your way may seem fairly flimsy and inconsequential. For their size, however, spider silk fibers are incredibly strong – enough so that scientists have long been trying to figure out what their secret is, so it can be applied to man-made materials. In a recently-published paper, German scientists claim to have gotten closer to the answer.
"Silk fibers exhibit astonishing mechanical properties. They have an ultimate strength comparable to steel, toughness greater than Kevlar and a density less than cotton or nylon," said senior study author Dr. Frauke Gräter from the Heidelberg Institute for Theoretical Studies. "Because silk fibers continue to outperform their artificial counterparts in terms of toughness, many studies have tried to understand the mechanical characteristics of these extraordinary natural fibers."
It has already been established that spider silk is made up of two types of building blocks, namely soft amorphous and strong crystalline subunit components. Utilizing what they described as "a multi-scale 'bottom-up' computational approach," Gräter's team analyzed the atomic make-up of these components, with an eye towards how they both ultimately contribute to the structure of the fiber. Via computer simulations, they studied the characteristics of individual and coupled subunits, and of complete fibers.
What they discovered was that the silk's elasticity and its ability to distribute mechanical stress comes courtesy of the soft amorphous subunits. Its maximal toughness is a product of the crystalline subunits, and is greatly affected by the way in which they are distributed throughout the fiber. Models incorporating different arrangements of the two types of subunits were then tried out, with Dr. Gräter determining that "a serial arrangement of the crystalline and amorphous subunits in discs outperformed a random or parallel arrangement, suggesting a new structural model for silk."
The research was published last month in Biophysical Journal.