The fluid mechanical properties of aqueous silk fibroin solutions

The impact of certain physiological factors such as concentration, purity, pH and salt concentration on the fluid mechanical properties, surface tension and viscosity of silk fibroin protein was assessed. Viscosity variation with rate of strain indicated changes in shear sensitivity while the surface tension provided insight into fibroin's change in surfactancy and correlated with the formation of micellar structures. Discussion was done in the context of the amphiphilic molecular structure of fibroin and correlations were found with in vivo events. The pH dependency of the shear response was correlated to the predicted isoelectric point pI. Metallic ions were shown to affect the pH dependency of the shear response and specifically Ca2+ ions provided a stabilizing effect on fibroin's conformational transitions. Sericin also had a similar effect, in that shear sensitivity was muted for a larger range of strain rates as compared to pure solutions. These correlations implied the presence of potential control mechanisms for the processing of aqueous fibroin solutions, assurance of safe storage of liquid silk and to enable the transport and spinning of fiber.