Nanofibers of silk fibroin controlled by the crystallization of polyethylene glycol in frozen solution

The conformation of silk flbroin (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.