Liquid crystals and flow elongation in a spider's silk production line

Abstract

Our observations on whole mounted major ampullate silk glands suggested that the thread is drawn from a hyperbolic die using a pre–orientated lyotropic liquid crystalline feedstock. Polarizing microscopy of the gland's duct revealed two liquid crystalline optical textures: a curved pattern in the feedstock within the ampulla of the gland and, later in the secretory pathway, the cellular texture previously identified in synthetic nematic liquid crystals. The behaviour of droplet inclusions within the silk feedstock indicated that elongational flow at a low shear rate occurs in the gland's duct and may be important in producing an axial molecular orientation before the final thread is drawn. Our observations suggested that the structure of the spider's silk production pathway and the liquid crystalline feedstock are both involved in defining the exceptional mechanical properties of spider dragline silk.