W0174

Structural Studies of Spider Silks. David T. Grubb, Dept of Materials Science and Engineering, Cornell University, NY, USA

Spider Silks are proteins that form fibers with mechanical properties exceeding those of synthetic fibers. Structural studies by fiber diffraction at synchrotron sources is complemented by NMR and other more local probes. But views of structure can be very different depending on the background of the researcher, "synthetic" or "biological". One sees a semi-crystalline block co-polymer, the other fragments of ß-sheet and turns in the protein.

X-ray diffraction at CHESS shows that dry dragline silk from Nephila clavipes is very like a synthetic fiber, with well-oriented very small crystallites in a partially oriented amorphous matrix. When wet the fiber softens and shrinks. The equilibrium shrunk state is oriented; the fiber behaves like a filled elastomer that was formed from oriented material. This agrees with studies that show a liquid crystalline intermediate state in-vivo. Attempts to process strong fibers from natural or bio-engineered protein have not succeeded.

Small-angle fiber scattering from wet silk is not normal, and so far, not understood. This leads us to simultaneous collection of wide and small angle data, and for dynamic studies of deformation, the use of scattering to determine the width and thickness of the sample in the beam. New CCD detector technology has made this relatively painless. In previous work, local stress and strain has not been available.

The samples we use are bundles, hundreds of fibers collected from one spider over a period of 20 - 40 minutes. Trials have shown that data can be obtained from 10 fibers at CHESS and from single fibers elsewhere, but using very small samples of a biological material leads to problems of reproducibility.

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