Amphiphilic Block Copolymers Bearing Ortho Ester Side-Chains: pH-Dependent Hydrolysis and Self-Assembly in Water

A new type of pH-responsive block copolymer nanoparticle has been synthesized and characterized. The amphiphilic diblock copolymer, PEG-b-PMYM, contains acid-labile ortho ester side-chains in the hydrophobic block and can self-assemble into micelle-like nanoparticles in water at neutral pH. Hydrolysis of the ortho ester side-chains follows a distinct exocyclic mechanism and shows pH-dependent kinetics, which triggers changes in nanoparticle size and morphology. The nanoparticles have been found to be non-toxic to cells in vitro. The ability to tune the size and morphology of biocompatible block copolymer nanoparticles by controlling the pH-sensitive side-chain hydrolysis represents a unique approach that may be exploited to improve the efficacy of nanometer-scale drug delivery.