TIT# Investigation of the nanofibril of silk fibers
AUT# Putthanarat, S.; Stribeck, N.; Fossey, S. A.; Eby, R. K.; Adams, W. W.;
SOU# Polymer (2000), 41, 7735-7747
LOC# xv057
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ABS# Silk from 3-molted, 4-molted and sex-limited Bombyx mori, Antheraea Pernyi
     and Antheraea Yamamai have been investigated using Atomic Force Microscopy
     and Low Voltage High Resolution Scanning Electron Microscopy. Nanofibrils,
     bundles of nanofibrils, helical features and a layered structure with a
     cross angle between nanofibrils in different layers were observed for all
     silks. Similar log-normal distributions of fibril widths were obtained
     from all silks with the geometric mean fibril widths covering the range
     of 90 - 170 nm. There is no correlation of the fibril width with the fibril
     size from different types of silkworm. similar normal distributions of
     cross angles were observed in 30 % of the images with the arithmetic means
     covering the range of  30 - 50°. There is an apparent correlation of
     cross angle with fiber size. The larger fibers for which the cyrstals
     are primarily alanine and glycine, 36°. Initial wide angle X-ray diffraction
     measurements on a single fiber of A. pernyi are consistent with the
     fraction of fibrils at different cross angles being 28 %. A simplified
     computer calculation method and molecular modeling were used in a search
     for packing angles which minimize the interaction energy of packing
     between beta sheets. Initial results reveal  no definitive evidence of
     epitaxy to account for the cross angles. It is proposed that a multifibrillar
     fiber offers a number of mechanical advantages over a solid fiber with the
     same cross sectional area.