Published online by Cambridge University Press: 25 February 2011
Transmitted polarized light microscopy of various natural silk secretions reveals their ability to form nematic liquid crystalline phases. Observations of microstructure, together with a simple secondary structure analysis of known amino acid sequences in silk proteins, suggest that the rodlike structures forming the nematic phase are supramolecular aggregates, rather than individual rigid molecular segments. The optical birefringence of dragline fiber produced by controlled silking depends on the linear haul-off velocity, and can exceed the birefringence of naturally spun fibers; this suggests the possibility of in-vitro spinning of silk to obtain values of strength and stiffness even greater than those achieved in vivo.