J. Nam et Yh. Park, Morphology of regenerated silk fibroin: Effects of freezing temperature, alcohol addition, and molecular weight, J APPL POLY, 81(12), 2001, pp. 3008-3021
Regenerated silk fibroin (RSF) was prepared by dissolving in a CaCl2/ ethan
ol/H2O solvent system, freezing, and lyophilization. The effect of freezing
temperature, alcohol addition, and molecular weight on the morphological a
nd conformational changes were investigated through scanning electron micro
scopy, X-ray diffraction, Fourier transform infrared spectroscopy, circular
dichroism spectroscopy, and differential scanning calorimetry analysis. Ho
wever, the addition of a small amount of methanol induced the morphological
change of RSF to a fine-particle aggregate, which resulted from the format
ion of a p-sheet crystalline structure. The lower the freezing temperature
was, the more the formation of aggregates was favored, and the finer powder
aggregates were formed. As the amount of added hydrophilic alcohol such as
methanol and ethanol increased in the silk fibroin solution, a spherical p
owder form was changed to fine aggregates with the enhancement of thermal s
tability and crystallinity. On the other hand, RSFs prepared with a hydroph
obic alcohol such as l-butanol or l-octanol showed a lump-like or sheet-lik
e shape of morphology without any changes in conformational transition. It
is concluded that the molecular weight of the silk fibroin and the type and
amount of alcohol were determining factors in the morphological features o
f RSF, especially the size and shape of fibroin particles. A uniform ultraf
ine powder of RSF with a spherical form (similar to 1 mum) can be obtained
when the molecular weight and the alcohol addition to the silk fibroin solu
tion are controlled. (C) 2001 John Wiley & Sons, Inc.