Using Dynamic Covalent Chemistry To Drive Morphological Transitions: Controlled Release of Encapsulated Nanoparticles from Block Copolymer Vesicles

Abstract

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, in situ release of encapsulated silica nanoparticles is achieved via vesicle dissociation at room temperature; moreover, the rate of release can be fine-tuned by varying the solution pH and/or the APBA concentration. Furthermore, this strategy also works (i) for relatively thick-walled vesicles that do not normally exhibit stimulus-responsive behavior and (ii) in the presence of added salt. This novel molecular recognition strategy to trigger morphological transitions via dynamic covalent chemistry offers considerable scope for the design of new stimulus-responsive copolymer vesicles (and hydrogels) for targeted delivery and controlled release of cargoes. In particular, the conditions used in this new approach are relevant to liquid laundry formulations, whereby enzymes require protection to prevent their deactivation by bleach.

New Insights into RAFT Dispersion Polymerization‐Induced Self‐Assembly: From Monomer Library, Morphological Control, and Stability to Driving Forces

“…More recently, molecular recognition strategies with tunable kinetics, including dynamic covalent chemistry and host−guest complexation, were utilized to trigger morphological transitions of PHPMA‐based vesicles. Specifically, binding of 3‐aminophenylboronic acid (APBA) with the pendent cis ‐diol groups of the PGMA stabilizer block of PGMA–PHPMA vesicles formed phenylboronate esters in mildly alkaline aqueous dispersion at ambient temperature ( Figure a) . This specific binding increased the effective volume of hydrophilic PGMA block, lowered the packing parameter, and thus induced a vesicle‐to‐worm/sphere transition (Figure b).…”

“…b) Schematic cartoon for vesicle‐to‐worm/sphere transition induced by selective binding of APBA to the PGMA stabilizer chains. Reproduced with permission . Copyright 2017, American Chemical Society.…”

Reactive and Functional Nanoobjects by Polymerization‐Induced Self‐Assembly

“…The re‐formed vesicles, however, are of different sizes and dispersities, owing to different self‐assembly conditions. Using 3‐aminophenylboronic acid as binding agent to the pendent cis ‐diol groups of PGMA allowed the phase transition of vesicles with thicker walls to worms at specific DP n,PHPMA . Compared with the end group–driven phase transition of similar nanoobjects described above, that is, HOOC‐PGMA‐ b ‐PHPMA, lateral‐group functionalization showed a higher transition rate and efficiency.…”

Controlling Nanomaterial Size and Shape for Biomedical Applications via Polymerization‐Induced Self‐Assembly

“…incorporated water‐soluble 3‐aminophenylboronic acid (APBA) into PGMA‐ b ‐PHPMA diblock copolymer vesicles. First, PISA was used to prepare PGMA‐ b ‐PHPMA diblock copolymer vesicles in concentrated aqueous solution . This diblock copolymer was chosen because i) the PGMA block contained pendent cis‐diol groups that could bind selectively to water‐soluble phenylboronic acid derivatives, and ii) the PHPMA block is weakly hydrophobic, which facilitates the desired order–order morphological transition.…”