Silk Reconstitution Disrupts Fibroin Self-Assembly

Abstract

Using\natomic force microscopy, we present the first molecular-scale\ncomparison of two of the most important silk dopes, native (NSF) and\nreconstituted (RSF) silkworm fibroin. We found that both systems depended\non shear to show self-assembly. Significant differences in the nature\nof self-assembly between NSF and RSF were shown. In the highest studied\nconcentration of 1000 mg/L, NSF exhibited assembly into 20–30\nnm-wide nanofibrils closely resembling the surface structures found\nin natural silk fibers. RSF, in contrast, showed no self-assembly\nwhatsoever at the same concentration, which suggests that the reconstitution\nprocess significantly disrupts silk’s inherent self-assembly\ncapability. At lower concentrations, both RSF and NSF formed fibrils\nunder shear, apparently denatured by the substrate. Using image analysis,\nwe quantified the properties of these self-assembled fibrils as a\nfunction of concentration and found low-concentration fibrils of NSF\nto form larger continuous structures than those of RSF, further supporting\nNSF’s superior self-assembly capabilities.