Branched peptide actuators for enzyme responsive hydrogel particles

We demonstrate the preparation of enzyme responsive poly(ethylene glycol) acrylamide hydrogel microparticles (mu PEGA) 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 mPEGA 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.