EVIDENCE OF A CHOLESTERIC LIQUID-CRYSTALLINE PHASE IN NATURAL SILK SPINNING PROCESSES

A look inside the silk spinning process along the length of a silk gla nd has been achieved by the cryogenic quenching and subsequent microto ming of live silk-spinning animals, Nephila clavipes (spider) and Bomb yx mori (silkworm). Observations made using transmission electron micr oscopy, electron diffraction and atomic force microscopy indicate a ch olesteric liquid crystalline phase of aqueous silk fibroin in the earl y duct portion of the major silk-producing gland in both species. Tran smission electron microscopy (TEM) and atomic force microscopy (AFM) p rovide evidence for the cholesteric intermediate phase. The fracture s urface produced by the diamond microtoming knife follows the twist of the director field, yielding thin sections with an undulating surface topography which produces a characteristic banding, on the order of 20 0-600 nm, in TEM and AFM images. Electron diffraction results also sup port the picture of the aqueous silk existing as a cholesteric at an i ntermediate stage in the spinning process.