Drug permeation through temperature-sensitive membranes prepared from poly(vinylidene fluoride) with grafted poly(N-isopropylacrylamide) chains

Temperature-responsive copolymers, poly(vinylidene fluoride)-graft-poly(N-isopropylacrylamide) (PVDF-g-PNIPAAM), were synthesized by thermally-induced graft copolymerization of N-isopropylacrylamide (NIPAAM) with the ozone-pretreated PVDF. Temperature-sensitive microfiltration membranes were then prepared from the PVDF-g-PNIPAAM copolymers by phase inversion. The chemical structure and composition of the PVDF-g-PNIPAAM copolymers were characterized by FT-IR spectroscopy and elemental analysis. X-ray photoelectron spectroscopy (XPS) analyses of the membranes revealed a substantial surface enrichment in grafted NIPAAM polymer. The pore sizes of the PVDF-g-PNIPAAM membranes were measured using a Coulter® Porometer. The temperature-dependent swelling behavior of the membranes in aqueous solution was studied by atomic force microscope (AFM) and water retention behavior. Increasing the surface graft concentration of the membrane resulted in a higher degree of temperature-sensitive swelling. The copolymer membranes also exhibited reversible temperature-dependent permeability to calcein and fluorescein isothiocyanate (FITC)–dextran in phosphate buffer solutions (pH 7.4), with the most drastic change in permeability being observed in the temperature range between 27 and 32 °C.