Ochi Akie, Hossain Khandker S, Magoshi Jun, Nemoto Norio
Department of Molecular and Material Sciences, IGSES, Kyushu University, Hakozaki, Fukuoka 812-8581, Japan.
Biomacromolecules. 2002 Nov-Dec;3(6):1187-96. doi: 10.1021/bm020056g.
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.
对从家蚕中部提取的丝素蛋白水溶液在0.08至27.5 wt%的宽聚合物浓度C范围内进行了动态光散射（DLS）和流变学测量。在C小于1 wt%的稀溶液区域获得的DLS结果与一个模型一致，该模型认为基本单元是由丝素蛋白和P25以6:1摩尔比组成的大蛋白质复合物。在稀C区域的流变学测量表明，那些流体动力学半径约为100 nm的单元（或聚集体）通过丝素蛋白分子的COO(-)离子与样品中存在的二价金属离子如Ca(2+)或Mg(2+)离子之间的离子键形成一个延伸到整个样品体积的网络，具有小的假平台模量，并且在达到屈服应力后，会诱导出稳定的塑性流动，其粘度比通过蠕变和蠕变恢复测量估计的零剪切粘度低4 - 6个数量级。在线性粘弹性区域测量的储能剪切模量G'(ω)和损耗剪切模量G''(ω)对角频率ω的依赖性表明，所有溶液在低ω区域都具有假平台模量，并且当C大于约4.2 wt%时样品变得高度粘弹性。在C = 11.2 wt%以上，另一个平台出现在高ω端，同时在中间ω区域G''有明显的最大值。对应于G''最大值的τ = 0.5 s的松弛运动是高C区域丝素蛋白溶液的特征性质之一。C = 27.5 wt%溶液的热流变行为表明，在丝腺MM部分形成的网络结构对温度敏感，通过将温度升高到T = 65℃可以实现更稳定的均匀网络。
