UsingDynamic Covalent Chemistry To Drive MorphologicalTransitions: Controlled Release of Encapsulated Nanoparticles fromBlock Copolymer Vesicles

摘要

Dynamic covalent chemistry is exploited to drive morphological order–order transitions to achieve the controlled release of a model payload (e.g., silica nanoparticles) encapsulated within block copolymer vesicles. More specifically, poly(glycerol monomethacrylate)–poly(2-hydroxypropyl methacrylate) (PGMA–PHPMA) diblock copolymer vesicles were prepared via aqueous polymerization-induced self-assembly in either the presence or absence of silica nanoparticles. Addition of 3-aminophenylboronic acid (APBA) to such vesicles results in specific binding of this reagent to some of the pendent cis-diol groups on the hydrophilic PGMA chains to form phenylboronate ester bonds in mildly alkaline aqueous solution (pH ∼ 10). This leads to a subtle increase in the effective volume fraction of this stabilizer block, which in turn causes a reduction in the packing parameter and hence induces a vesicle-to-worm (or vesicle-to-sphere) morphological transition. The evolution in copolymer morphology (and the associated sol–gel transitions) was monitored using dynamic light scattering, transmission electron microscopy, oscillatory rheology,and small-angle X-ray scattering. In contrast to the literature, insitu release of encapsulated silica nanoparticles is achieved viavesicle dissociation at room temperature; moreover, the rate of releasecan be fine-tuned by varying the solution pH and/or the APBA concentration.Furthermore, this strategy also works (i) for relatively thick-walledvesicles that do not normally exhibit stimulus-responsive behaviorand (ii) in the presence of added salt. This novel molecular recognitionstrategy to trigger morphological transitions via dynamic covalentchemistry offers considerable scope for the design of new stimulus-responsivecopolymer vesicles (and hydrogels) for targeted delivery and controlledrelease of cargoes. In particular, the conditions used in this newapproach are relevant to liquid laundry formulations, whereby enzymesrequire protection to prevent their deactivation by bleach.