STRUCTURAL-CHANGES OF SILK FIBROIN MEMBRANES INDUCED BY IMMERSION IN METHANOL AQUEOUS-SOLUTIONS

Structural changes of native and regenerated silk fibroin membranes we re induced by immersion in water-methanol solutions and examined as a function of immersion time and methanol concentration. X-ray diffracto metry and infrared spectroscopy data showed that transition from rando m coil to beta-sheet structure occurred favorably when both native and regenerated silk fibroin membranes were immersed in water-methanol so lutions, regardless of the different immersion time. Only native silk membrane, treated for 2 min with pure methanol, maintained its origina l amorphous structure, as demonstrated by differential scanning calori metric (DSC) curves. The degree of displacement, measured by thermomec hanical analysis (TMA), was much greater for regenerated than for nati ve silk fibroin membranes. SDS-PAGE pattern showed that native silk fi broin has a molecular weight of 350, while the regenerated sample is f ormed by a large number of polypeptides in the range of 200-50 KD. The amount of acidic and basic amino acids decreased slightly in regenera ted silk fibroin. Physical properties of silk membranes treated with w ater-methanol solutions are discussed in terms of membrane structure, treatment conditions, and chemical structure of starting material. (C) 1994 John Wiley & Sons, Inc.