Rheology and Dynamic Light Scattering of Silk Fibroin Solution Extracted from the Middle Division ofBombyx moriSilkworm

Abstract

Dynamic light scattering (DLS) and rheological measurements were performed on aqueous silk fibroin solutions extracted from the middle division of Bombyx mori silkworm over a wide range of polymer concentration C from 0.08 to 27.5 wt %. DLS results obtained in the dilute region of C less than 1 wt % are consistent with a model that an elementary unit is a large protein complex consisting of silk fibroin and P25 with a 6:1 molar ratio. Rheological measurements in the dilute C region reveal that those units (or clusters) with the hydrodynamic radius of about 100 nm form a network extending over the whole sample volume with small pseudoplateau modulus mainly by ionic bonding between COO(-) ions of the fibroin molecules and divalent metallic ions such as Ca(2+) or Mg(2+) ions present in the sample and also that, after a yield stress is reached, steady plastic flow is induced with viscosity much lower than the zero-shear viscosity estimated from creep and creep recovery measurements by 4-6 orders of magnitude. Angular frequency omega dependencies of the storage and the loss shear moduli, G'(omega) and G' '(omega), measured in the linear viscoelastic region, indicate that all solutions possess the pseudoplateau modulus in the low omega region and samples become highly viscoleastic for C greater, similar 4.2 wt %. Above C = 11.2 wt % another plateau appears at the high omega end accompanied by a distinct maximum of G' ' in the intermediate omega region. The relaxation motion with tau = 0.5 s corresponding to the maximum of G' ' is one of characteristic properties of the fibroin solutions in the high C region. Thermorheological behaviors of the solution with C = 27.5 wt % show that the network structure formed in the MM part of the silk gland is susceptible to temperature and a more stable homogeneous network is realized by raising the temperature up to T = 65 degrees C.

Deposition of bone‐like apatite on modified silk fibroin films from simulated body fluid

“…The calcium ions were probably stabilized on the ␤-sheet structure of the silk fibroin. 48,49 In this study, the addition of calcium ions increased the portion of ␤-sheet structure. The calcium ions, however, were not tightly bonded to the ␤-sheet structure, as they eluted rapidly from the SFFs.…”

Silk Fibroin‐Regulated Crystallization of Calcium Carbonate

“…Previous studies have shown that the silk fibroin is present in the dilute solution as aggregates (or clusters) composed of several large protein complexes, which presumably are induced by hydrophobic interactions among the hydrophobic parts of the fibroin chains. [28][29][30] Comparable to typical amphoteric block copolymers, the aggregation of silk fibroin in the solution is probably easier when its molecule distributes in a narrower and higher region.…”

Carbon-decorated iron oxide hollow granules formed using a silk fibrous template: lithium-oxygen battery and wastewater treatment applications

“…23,24 Generally, it is believed that hydrophobic/hydrophilic block copolymer structures may be assembled into β-crystallites via the nanofibrillar cross-linked network of the silk fibroin in solution ( Figure 1c). [24][25][26][27] Analysis of the particle size distribution and zeta potential showed that the silk fibroin in the solution underwent aggregation when the temperature of the solution increased (Figure 1d). This behavior probably involves interaction with Fe 3+ , and thus the silk fibroin acts as a template for crystallization.…”