A novel methodology to explore the viscoelasticity of spider major ampullate silk.

Even before material science was a recognized discipline, the amazing mechanical properties of spider silk were documented and became the object of much study. In addition to the exceptional material properties of spider silk and the reported low immunogenicity, its concatenated amino acid motif arrangement facilitates a distinct possibility of manipulating the silk to create a designer biomaterial for medical applications. Crystalline protein regions imbedded in a mobile protein matrix give it a distinct set of viscoelastic abilities. Consequently, elasticity cannot be simply quantified by only measuring extensibility. To understand how the sequence of the major ampullate proteins affects elasticity, the hysteresis of single fibers from two different species, Argiope aurantia and Nephila clavipes, were examined using cyclic loading and unloading. The yield point that discriminates a transition from elastic extension to a plastic extension was analyzed by examining three different properties: Young's modulus, energy recovery and slack in the fiber after recovery. Young's modulus remained relatively constant regardless of the cycle. However, the energy recovered decreased as the slack and cycle number increased. Large standard deviations masked any quantitative differences between species and substantiated the necessity of developing synthetic silk to harness the amazing mechanical properties of spider silk.