pH-Responsive Diblock Copolymer Vesicles via Polymerization-Induced Self-Assembly in Aqueous Media: Synthesis, Loading, and Potential Biological Applications

Polymerization-induced self-assembly (PISA) offers a useful strategy for the efficient encapsulation of biomacromolecules within diblock copolymer vesicles under mild conditions. This approach eliminates the need for a separate vesicle loading step and should be particularly advantageous for drug delivery applications if suitable biocompatible vesicles can be designed to release their encapsulated cargo in response to a specific environmental stimulus. Ideally, the vesicles should remain intact after endocytosis but subsequently undergo dissociation when exposed to the mildly acidic conditions (pH ~5) found within intracellular endosomal compartments of mammalian cells. In this study, reversible addition-fragmentation chain-transfer (RAFT) aqueous dispersion copolymerization of 2-hydroxypropyl methacrylate (HPMA) with 2-N-(morpholino)ethyl methacrylate (MEMA) was conducted using a water-soluble poly(glycerol monomethacrylate) (PGMA) precursor to prepare a series of PGMA-P(HPMA-stat-MEMA) copolymer vesicles. Such vesicles exhibit tunable pH-responsive behavior, leading to their dissociation between pH 3.5 and 6 depending on their MEMA content. F(ab) antibody fragments were loaded within these vesicles during their aqueous PISA synthesis at 45 °C with an encapsulation efficiency of 42 ± 4%: this antibody retains its antigen-binding functionality and is subsequently released from the vesicles at pH =5.25. Furthermore, nanoflow cytometry analysis confirms the encapsulation of plasmid DNA within these vesicles and their subsequent take-up by human keratinocytes highlights the versatility of this technique for biotherapeutic delivery. This is the first reported example of PISA being used to prepare vesicles loaded with either antibody fragments or nucleic acids that can be subsequently released under physiologically relevant conditions, without requiring additional reactions or postpolymerization loading steps. In principle, encapsulation of proteins, antibodies, enzymes, or oligonucleotides within vesicles during their PISA synthesis has the potential to significantly advance nanomedicine.