Spider major ampullate silk (drag line): Smart composite processing based on imperfect crystals

A spider can spin major ampullate silk (drag line) at rates that differ by more than an order of magnitude, and yet obtain consistently reliable tensile properties. Silk samples collected at different rates and stained by infiltration with tin were studied by transmission electron microscopy. The stained microstructures indicate the presence of nonperiodic lattice crystals, the average size of which depends on the silking rate. A simple statistical point model demonstrates that the ordered regions in major ampullate silk can originate from statistical matches between adjacent chains, The minimum size of the ordered regions is dictated by the fixed monomer sequence in the chains and not by processing kinetics, Inductively coupled plasma-mass spectroscopy shows that the concentration of multivalent protein-binding cations in the unstained fibre is significantly reduced at the higher rates of silking, compared with their concentration at the lowest rates, Qualitatively, this result is consistent with the ions being used to maintain the shear sensitivity of silk secretion over the range of processing rates studied.