POROUS MEMBRANE OF BOMBYX-MORI SILK FIBROIN - STRUCTURE CHARACTERIZATION, PHYSICAL-PROPERTIES AND APPLICATION TO GLUCOSE-OXIDASE IMMOBILIZATION

Porous membranes of Bombyx mori silk fibroin were prepared by removal of polyethyleneglycol (PEG) from a silk fibroin-PEG mixed membrane in order to obtain high substrate permeability. The structure characterization of the porous membrane was investigated by means of C-13 cross-polarization nuclear magnetic resonance (NMR) spectra and scanning electron microscopy. According to the NMR spectra obtained, the fraction of the Silk II, which exists as anti-parallel beta-sheets in the porous silk fibroin membrane, was observed to be 60-65%. An increase of the permeabilities of glucose and NaCl by a factor of more than 20 was observed when the weight ratio of PEG to silk fibroin was increased to 3.0. The H-1-NMR spin-lattice relaxation times for water in the porous silk fibroin membranes were analyzed as two components, fast (14-26 msec) and slow (274-1385 msec), suggesting constrained motion of the water molecules in the NMR time scale in the silk fibroin membrane. The logarithmic permeability coefficients of glucose and NaCl decrease linearly with increasing relaxation rates of the slow components of the water. Glucose oxidase was immobilized with these porous membranes, and a sensing system for monitoring the glucose concentration was constructed. Detailed analysis of the output vs. glucose concentration data suggests that simultaneous reaction and diffusion control occur in these membranes.