Photo- and Reduction-Responsive Polymersomes for Programmed Release of Small and Macromolecular Payloads

We report on the preparation of photo- and reduction-responsive diblock copolymers through reversible addition fragmentation chain transfer (RAFT) polymerization of a coumarin-based disulfide-containing monomer (i.e., CSSMA) using a poly(ethylene oxide) (PEO)-based macro RAFT agent. The resulting amphiphilic PEO-b-PCSSMA copolymers self-assembled into polymersomes with hydrophilic PEO shielding coronas and hydrophobic bilayer membranes. Upon irradiating the polymersomes with visible light (e.g., 430 nm), the coumarin moieties within the bilayer membranes were cleaved with the generation of primary amine groups, which spontaneously underwent inter/intrachain amidation reactions with the ester moieties, thereby tracelessly cross linking and permeating the bilayer membranes. Notably, this process only gave rise to the release of small molecule payloads (e.g., doxorubicin hydrochloride, DOX) while large molecule encapsulants (e.g., Texas red-labeled dextran, TR-dextran) were retained within the cross-linked polymersomes due to the preservation of the integrity of the vesicular nanostructures. However, cross-linked polymersomes undergo further structural disintegration upon incubation with glutathione (GSH) due to the scission of disulfide linkages, resulting in the release of macromolecular payloads. Thus, dual-stimuli responsive polymersomes with tracelessly cross-linkable characteristics enable sequential release of payloads with spatiotemporal precision, which could be of promising applications in synergistic loading and programmed release of therapeutics.