Biocompatible hydrogels have many applications, ranging from contact lenses to tissue engineering scaffolds. In most cases, rigorous sterilization is essential. Herein we show that a biocompatible diblock copolymer forms wormlike micelles via polymerization-induced self-assembly in aqueous solution. At a copolymer concentration of 10.0 w/w %, interworm entanglements lead to the formation of a free-standing physical hydrogel at 21 °C. Gel dissolution occurs on cooling to 4 °C due to an unusual worm-to-sphere order-order transition, as confirmed by rheology, electron microscopy, variable temperature (1)H NMR spectroscopy, and scattering studies. Moreover, this thermo-reversible behavior allows the facile preparation of sterile gels, since ultrafiltration of the diblock copolymer nanoparticles in their low-viscosity spherical form at 4 °C efficiently removes micrometer-sized bacteria; regelation occurs at 21 °C as the copolymer chains regain their wormlike morphology. Biocompatibility tests indicate good cell viabilities for these worm gels, which suggest potential biomedical applications.

RAFT-mediated polymerisation-induced self-assembly (PISA) is used to prepare six types of amphiphilic block copolymer nanoparticles which were subsequently evaluated as putative Pickering emulsifiers for the stabilisation of n-dodecane-in-water emulsions. It was found that linear poly(glycerol monomethacrylate)-poly(2-hydroxypropyl methacrylate) (PGMA-PHPMA) diblock copolymer spheres and worms do not survive the high shear homogenisation conditions used for emulsification. Stable emulsions are obtained, but the copolymer acts as a polymeric surfactant; individual chains rather than particles are adsorbed at the oil-water interface. Particle dissociation during emulsification is attributed to the weakly hydrophobic character of the PHPMA block. Covalent stabilisation of these copolymer spheres or worms can be readily achieved by addition of ethylene glycol dimethacrylate (EGDMA) during the PISA synthesis. TEM studies confirm that the resulting cross-linked spherical or worm-like nanoparticles survive emulsification and produce genuine Pickering emulsions. Alternatively, stabilisation can be achieved by either replacing or supplementing the PHPMA block with the more hydrophobic poly(benzyl methacrylate) (PBzMA). The resulting linear spheres or worms also survive emulsification and produce stable n-dodecane-in-water Pickering emulsions. The intrinsic advantages of anisotropic worms over isotropic spheres for the preparation of Pickering emulsions are highlighted. The former particles are more strongly adsorbed at similar efficiencies compared to spheres and also enable smaller oil droplets to be produced for a given copolymer concentration. The scalable nature of PISA formulations augurs well for potential applications of anisotropic block copolymer nanoparticles as Pickering emulsifiers.

A series of diblock copolymer worms are prepared via aqueous dispersion polymerization using reversible addition-fragmentation chain transfer (RAFT) polymerization chemistry. More specifically, a poly(glycerol monomethacrylate) (PGMA) RAFT chain transfer agent is used to polymerize a watermiscible monomer, 2-hydroxypropyl methacrylate, at 70 C. The poly(2-hydroxypropyl methacrylate) (PHPMA) chains become increasingly hydrophobic as they grow, which leads to nanoparticle formation. Careful control of the diblock composition is achieved by fixing the mean degree of polymerization (DP) of the PGMA stabilizer block at 54 and systematically varying the DP of the coreforming PHPMA block. This strategy enables the worm phase space to be targeted reproducibly. These worms form soft free-standing gels in aqueous solution due to inter-worm entanglements. Rheological studies enable the influence of the diblock copolymer composition on the gel strength, critical gelation concentration (CGC) and critical gelation temperature (CGT) to be assessed. A maximum in gel strength is observed as the DP of the PHPMA block is increased from 130 to 170. The initial increase is due to longer worms, while the subsequent decrease is associated with worm clustering, which leads to more brittle gels. The gel strength is reduced from approximately 100 Pa to 10 Pa as the copolymer concentration is lowered from 10 to 5 w/w%, with a CGC being observed at around 3 to 4 w/w%. The CGT is relatively concentration-independent, but sensitive to the diblock copolymer composition: longer (more PHPMA-rich) chains lead to the CGT being reduced from 20 C to 7 C. This is because longer PHPMA blocks require a greater degree of hydration to induce the worm-to-sphere transition, which can only achieved at progressively lower temperatures. Reversible de-gelation also occurs on cooling, since there can be no entanglements between isotropic particles. This RAFT formulation also provides a rare example of thermo-responsive diblock copolymer worms.

Hydroxy-functionalized polymersomes (or block copolymer vesicles) were prepared via a facile one-pot RAFT aqueous dispersion polymerization protocol and evaluated as Pickering emulsifiers for the stabilization of emulsions of n-dodecane emulsion droplets in water. Linear polymersomes produced polydisperse oil droplets with diameters of ~50 μm regardless of the polymersome concentration in the aqueous phase. Introducing an oil-soluble polymeric diisocyanate cross-linker into the oil phase prior to homogenization led to block copolymer microcapsules, as expected. However, TEM inspection of these microcapsules after an alcohol challenge revealed no evidence for polymersomes, suggesting these delicate nanostructures do not survive the high-shear emulsification process. Thus the emulsion droplets are stabilized by individual diblock copolymer chains, rather than polymersomes. Cross-linked polymersomes (prepared by the addition of ethylene glycol dimethacrylate as a third comonomer) also formed stable n-dodecane-in-water Pickering emulsions, as judged by optical and fluorescence microscopy. However, in this case the droplet diameter varied from 50 to 250 μm depending on the aqueous polymersome concentration. Moreover, diisocyanate cross-linking at the oil/water interface led to the formation of well-defined colloidosomes, as judged by TEM studies. Thus polymersomes can indeed stabilize colloidosomes, provided that they are sufficiently cross-linked to survive emulsification.