Self‐assembly of regenerated silk fibroin from random coil nanostructures to antiparallel β‐sheet nanostructures

In this work, we studied the effects of incubation concentration and time on the self‐assembly behaviors of regenerated silk fibroin (RSF). Our results showed the assembly ways of RSF were concentration‐dependent and there were four self‐assembly ways of RSF: (i) At relatively low concentration (≤0.015%), RSF molecules assembled into protofilaments (random coil), and then the thickness decreased and the secondary conformation changed to antiparallel β‐sheet; (ii) at the concentration of 0.015%, RSF molecules assembled into protofilaments (random coil), and then assembled into protofibrils (antiparallel β‐sheet). The protofibrils experienced the appearance and disappearance of phase periodic intervals in turn; (iii) at the concentration of 0.03%, RSF molecules assembled into bead‐like oligomers (random coil), and then assembled into protofibrils (antiparallel β‐sheet), and finally the height and phase periodic intervals of RSF protofibrils disappeared in turn; and (iv) at the relatively high concentration (≥0.15%), RSF molecules assembled into protofilaments (random coil), then aggregated into blurry cuboid‐like micelles (random coil), and finally self‐arranged to form smooth and clear cuboid‐like micelles (antiparallel β‐sheet). These results provide useful insights into the process by which the RSF molecules self‐assemble into protofilaments, protofibrils and micelles. Furthermore, our work will be beneficial to basic understanding of the nanoscale structure formations in different silk‐based biomaterials. © 2014 Wiley Periodicals, Inc. Biopolymers 101: 1181–1192, 2014.