Poly(N-isopropylacrylamide)-gelatin hydrogel membranes with thermo-tunable pores for water flux gating and protein separation

Herein, a hybrid hydrogel was prepared by polymerizing N-isopropylacrylamide (NIPAAm) in the presence of gelatin and mixed with 300 nm polystyrene nanospheres (PNs) to cross-link the gelatin. A thermo-responsive polyNIPAAm(PNIPAAm)-gelatin hybrid hydrogel (NGHH) membrane was obtained after removing the lodged PNs from the NGHH. At the PNIPAAm-to-gelatin content ratio of 1, PNIPAAm in the NGHH membrane extended to completely occupy the pores left by PNs below the lower critical solution temperature (LCST), forming a pore-less membrane. Contrarily, above the LCST, phase separation of PNIPAAm occurred, resulting in pores in the membrane. This pore closing and opening below and above the LCST changed the water flux through the NGHH membranes, indicating the excellent water gating efficiency of these membranes. Accordingly, we applied these membranes as protein valves to separate lysozyme (Lys) and bovine serum albumin (BSA) of different sizes. At both 25 and 5 degrees C, smaller Lys could be transported through the hydrogen bonding channels of the pore-less membrane, whereas larger BSA was blocked by this membrane at 25 degrees C and transported through the pore-rich membrane at 45 degrees C. Thus, this biocompatible and stable NGHH membrane functioned as a biological selective valve, allowing protein separation.