Spider Silk: The Toughest Natural Polymer
In this chapter we review the properties and characterization of spider silk, particularly dragline silk, which is attracting increasing interest due to its marvelous properties. The spider's unique protein dope and natural spinning process play important roles in providing this unrivalled material with its characteristic structure that determines its strong and tough properties. In general, dragline silk is a semicrystalline material composed of crystallites embedded in an amorphous matrix. We introduce the widely applied techniques used to probe the structural characteristics of dragline silk. The inherent excellent mechanical properties of dragline silk, as well as the influence of silking conditions its mechanical properties, are reviewed. Models relating the structure to the mechanical properties are discussed, aiming to unravel the structural base for the unique mechanical properties. Supercontraction and cyclic contraction are two other interesting inherent properties of dragline silk; the former can maintain tension in a web after deformation by natural elements and the latter has the ability to perform work by subjecting the silk fibre to periodic cycling at high and low humidity. Current advances in possible applications of dragline silk in the biomedical and clinical fields using biomaterials of different forms, based on recombinant and reconstituted silk proteins, are discussed finally.