Responsive membranes with variable permeability, specifically the membranes in which pore size can be regulated in response to external stimuli, have a variety of applications: liquid flow regulation, size- and charge-selective filtration, controlled release, and sensors. We have developed novel multi-responsive thin-film membranes from a biopolymer hydrogel suitable for biomedical applications.

The membranes are multi-responsive in the sense that they combine functions of stimuli-responsive control and regulation of the mass transport with a range of properties such as chemical/biochemical reactor, catalysis of chemical reactions, antimicrobial activity, and optical signal transduction.

The porous hydrogel membranes were prepared through phase separation in partially miscible polymer blends followed by crosslinking of one of the polymers and extraction of another. In particular, three different phase-separation processes have been explored: i) salt induced phase separation in a soluble electrostatic complex of sodium alginate and gelatin, ii) phase separation in a blend solution of sodium alginate and poly(vinyl alcohol) interacting via hydrogen bonds and iii) phase separation in a solution blend of sodium alginate and diaminopropyl-terminated poly(ethylene glycol) having electrostatic and hydrogen bond interactions.

It has been demonstrated that signal-responsive thin hydrogel membranes could be coupled with enzyme-based systems to yield “smart” multisignal-responsive hybrid systems with built-in “logic”. The enzyme systems transduced biochemical input signals into structural changes of the membrane, thus resulting in the amplification of the biochemical signals and their transformation into the gated transport of molecules through the membrane.

An efficient optical signal transduction scheme has been demonstrated for the signal-responsive thin hydrogel film integrated into a plasmonic device. The device explores the effect of tunable plasmon coupling between silver nanoislands on the transparent support and silver nanoparticles located in the film that is actuated by the pH-responsive gel. This film is sensitive to pH changes related to biocatalytic processes. The well pronounced optical effect can be used for biosensing and study of local dynamical changes in stimuli-responsive materials. The membranes demonstrate a rapid response to external stimuli and antifouling properties. Most of these functions can be tuned by pH changes in the pH range relevant to biological systems (from pH 4 to 7).

The developed multifunctional responsive gel membrane is a promising platform for the development of “smart” devices for bioseparation, biosensors, and “smart” drug release.