Nanofibers of Silk Fibroin Controlled by the Crystallization of Polyethylene Glycol in Frozen Solution

The conformation of silk fibroin (SF) frozen with polyethylene glycol (PEG) at a molecular weight from 2 kDa to 20 kDa and a mass ratio of PEG:SF from 1:5 to 10:1 was studied by spectral and microscopic methods. It is found that the conformation transition of SF from random coil to β-sheet could be induced by the stress resulting from PEG crystallization at −20 °C, and greatly depended on the cooling rate, PEG:SF mass ratio and PEG molecular weight. These findings provide a new method for the preparation of desired SF nanofibers.