We have carried out studies on the rheological properties of regenerated silk
fibroin (RSF) solution using video microscopy. The degummed silk from the
Bombyx mori silkworm was used to prepare RSF solution by dissolving it in
calcium nitrate tetrahydrate-methanol solvent. Measurements were carried out by
tracking the position of an embedded micron-sized polystyrene bead within the
RSF solution through video imaging. The time dependent mean squared
displacement (MSD) of the bead in solution and hence, the complex shear modulus
of this solution was calculated from the bead's position information. An
optical tweezer was used to transport and locate the bead at any desired site
within the micro-volume of the sample, to facilitate the subsequent free-bead
video analysis. We present here the results of rheological measurements of the
silk polymer network in solution over a frequency range, whose upper limit is
the frame capture rate of our camera, at full resolution. By examining the
distribution of MSD of beads at different locations within the sample volume,
we demonstrate that this probe technique enables us to detect local
inhomogeneties at micrometer length scales, not detectable either by a
rheometer or from diffusing wave spectroscopy.Comment: 5 page