A Non-Periodic Lattice Model for Crystals in Nephila clavipes Major Ampullate Silk

Abstract

Defects play a significant role in determining the physical and thermodynamic behaviors of a material. This precept can be especially helpful when one attempts to interpret the engineering properties of a biological material in the context of its complex, hierarchical microstructure. An excellent example of an impressive engineering material used by nature is silk, which has a composite microstructure assembled from one or more protein polymers. Spiders, aided by several million years of evolution, have succeeded in producing a polymer fiber [major ampullate silk (MAS)] with a strength-to-weight ratio exceeding that of nearly all synthetic materials. Even the exceptions—specialty fibers such as carbon, silica, and some variants of Kevlar—pale in comparison when toughness (energy required to bring about failure) is taken into account; they are relatively brittle and lack the viscoelastic extensibility of MAS. When one considers that spiders produce this naturally biodegradable material under ambient conditions and with an aqueous solvent, the feat becomes even more impressive. It is clear that the spider could be an excellent instructor in both polymer processing and microstructural design.where the α-carbon is bonded to a functional “R” group that distinguishes the monomer as being one of the 20 commonly occurring natural a-amino acids.