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The first nanoprecipitation study of hydrophobic branched vinyl polymers is presented with control across a wide range of particle diameters (approximately 60–800 nm) from control of degree of polymerisation and precipitation parameters. In contrast to linear polymers of identical primary chain length, the formation of stable nanoparticles in aqueous media appears to be architecture driven with a contribution from oligomeric chain-ends with measureable water-solubility. The aqueous nanoparticles dispersions are robust and stable to dilution, solvent addition, sonication and temperature. The addition of small amounts of NaCl led to a destabilisation indicating charge stabilisation is also a major contributor to stability.

We demonstrate the preparation of enzyme responsive poly(ethylene glycol) acrylamide hydrogel microparticles (µPEGA) functionalised by solid phase synthesis with new branched peptide actuators. Branched peptide actuators provide enhanced charge density and overcome electrostatic screening at physiological ionic strength when compared to linear ones which do not show triggered swelling under these conditions. Particle swelling was induced by enzymatic hydrolysis which caused a change in the charge balance of the branched peptide actuators from zwitterionic (neutral) to cationic. Analysis of enzymatic activity and accessibility was undertaken using fluorescence labelling and two-photon microscopy. These experiments revealed that thermolysin could access the core of particles when linear peptides are used, while access was restricted to the surface when using branched actuators. These responsive µPEGA particles were then loaded with a fluorescent labeled dextran by application of a sequential pH change. The payload could be selectively released at physiological ionic strength when exposed to the target enzyme.