Microrheological Studies of Regenerated Silk Fibroin Solution by Video Microscopy

TL;DR

This study uses video microscopy to analyze the microrheological properties of regenerated silk fibroin solution, revealing local inhomogeneities and providing detailed insights into its viscoelastic behavior at microscopic scales.

Contribution

It introduces a novel microrheological measurement method using video microscopy and optical tweezers to study silk fibroin solutions at micrometer resolution.

Findings

Detected local inhomogeneities in silk fibroin solution

Measured complex shear modulus over a broad frequency range

Demonstrated the technique's ability to reveal microscale heterogeneities

Abstract

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.