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.
Highlights
Are excellent candidates for use as smart carriers and nanoreactors.[1−18] It is well-known that amphiphilic diblock copolymers with an appropriate hydrophilic−hydrophobic balance can self-assemble into vesicles (a.k.a. polymersomes) in aqueous solution.[19−24] Various types of functional diblock copolymers can be synthesized with defined composition and controllable molecular weight using living radical polymerization, which enables preparation of stimulus-responsive copolymer vesicles for the encapsulation and controlled release of active payloads.[25−40] In principle, disruption of vesicle membranes should be much more efficient than membrane swelling for the release of larger cargoes such as macromolecules or nanoparticles
A PGMA45 macromolecular chain transfer agent was synthesized by reversible addition−fragmentation chain transfer (RAFT) solution polymerization of glycerol monomethacrylate (GMA) in ethanol using a 2-cyano-2-propyl dithiobenzoate (CPDB) chain transfer agent (CTA) and 2,2′
Unlike earlier vesicle dissociation mechanisms based on the thermoresponsive nature of the membrane-forming PHPMA block or the ionization of functional groups located on the stabilizer terminus, this approach works well at ambient temperature, in the presence of relatively high levels of added salt, and even for thick-walled vesicles that do not normally exhibit thermosensitivity
Summary
Stimulus-responsive vesicles consisting of polymers, lipids, etc. are excellent candidates for use as smart carriers and nanoreactors.[1−18] It is well-known that amphiphilic diblock copolymers with an appropriate hydrophilic−hydrophobic balance can self-assemble into vesicles (a.k.a. polymersomes) in aqueous solution.[19−24] Various types of functional diblock copolymers can be synthesized with defined composition and controllable molecular weight using living radical polymerization, which enables preparation of stimulus-responsive copolymer vesicles for the encapsulation and controlled release of active payloads.[25−40] In principle, disruption of vesicle membranes should be much more efficient than membrane swelling for the release of larger cargoes such as macromolecules or nanoparticles. Are excellent candidates for use as smart carriers and nanoreactors.[1−18] It is well-known that amphiphilic diblock copolymers with an appropriate hydrophilic−hydrophobic balance can self-assemble into vesicles (a.k.a. polymersomes) in aqueous solution.[19−24] Various types of functional diblock copolymers can be synthesized with defined composition and controllable molecular weight using living radical polymerization, which enables preparation of stimulus-responsive copolymer vesicles for the encapsulation and controlled release of active payloads.[25−40] In principle, disruption of vesicle membranes should be much more efficient than membrane swelling for the release of larger cargoes such as macromolecules or nanoparticles In this context, there are various literature examples of vesicle dissociation to afford molecularly dissolved copolymer chains (a so-called order−disorder transition), whereby the membrane-forming hydrophobic block is rendered hydrophilic in situ.[41−47] In contrast, vesicleto-worm or vesicle-to-sphere order−order transitions have been recently reported, which can be used to trigger the ondemand release of encapsulated nanoparticle cargoes.[48−51].
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