Preparation and characterization of α-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)] with starch, as a macropore forming agent, on nonwoven polyester was prepared. The membranes could swell and de-swell around the characteristic lower critical solution temperature (LCST) of poly(N-isopropylacrylamide) (PNIPAAm). It was demonstrated that the presence of macropores in the membranes could improve the immobilization efficiency as well as lead to a short responding time upon temperature change across the LCST. Immobilized α-amylase could retain as high as 33% of the activity of the free enzyme with a loading level of 0.60-0.65 mg/cm² when the membrane preparation and enzyme immobilization 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 than 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 temperature was raised above or reduced below the LCST.