Preparation and characterization of alpha-amylase-immobilized thermal-responsive composite hydrogel membranes

Composite hydrogel membranes of crosslinked poly(N-isopropylacrylamide-co-N -acryloxysuccinimide-co-2-hydroxyethyl methacrylate) [P(NIPAAm-NAS-HEMA)] w ith starch, as a macropore forming agent, on nonwoven polyester was prepare d. The membranes could swell and de-swell around the characteristic lower c ritical solution temperature (LCST) of poly(N-isopropylacrylamicle) (PNIPAA m). It was demonstrated that the presence of macropores in the membranes co uld improve the immobilization efficiency as well as lead to a short respon ding time upon temperature change across the LCST. Immobilized a-amylase co uld retain as high as 33% of the activity of the free enzyme with a loading level of 0.60-0.65 mg/cm(2) when the membrane preparation and enzyme immob ilization conditions were optimized. The half time (T-0.5) for the swelling or de-swelling response of the gel phase within the membranes was less tha n 2 min, and the 90% time (T-0.9) was less than 6 min. The permeability for maltose through the membranes could change as much as 4.9-fold when the te mperature was raised above or reduced below the LCST. (C) 1999 John Wiley & Sons, Inc.