Roger J. Coulston

One-Step Fabrication of Supramolecular Microcapsules from Microfluidic Droplets

Be My Guests For a range of applications, including medical diagnostics or drug delivery, it is necessary to encapsulate one or more components into a microcapsule. While there are many methods that can do this, most either produce a range of capsule size or are not easily scalable for making large quantities. J. Zhang et al. (p. 690) developed a microfluidic-based system for making capsules using host-guest chemistry. Cucurbit[8]uril, which readily forms complexes in water, was used as the host molecule and could accommodate two different guest molecules. Rapid complexation was observed of methyl viologen–modified gold nanoparticles and a naphthol-containing copolymer. A molecular host that binds two guests directs scalable fabrication of hollow polymer/gold nanoparticle hybrid structures. Although many techniques exist for preparing microcapsules, it is still challenging to fabricate them in an efficient and scalable process without compromising functionality and encapsulation efficiency. We demonstrated a simple one-step approach that exploits a versatile host-guest system and uses microfluidic droplets to generate porous microcapsules with easily customizable functionality. The capsules comprise a polymer-gold nanoparticle composite held together by cucurbit[8]uril ternary complexes. The dynamic yet highly stable micrometer-sized structures can be loaded in one step during capsule formation and are amenable to on-demand encapsulant release. The internal chemical environment can be probed with surface enhanced Raman spectroscopy.

In Situ SERS Monitoring of Photochemistry within a Nanojunction Reactor

We demonstrate a powerful SERS-nanoreactor concept composed of self-assembled gold nanoparticles (AuNP) linked by the sub-nm macrocycle cucurbit[n]uril (CB[n]). The CB[n] functions simultaneously as a nanoscale reaction vessel, sequestering and templating a photoreaction within, and also as a powerful SERS-transducer through the large field enhancements generated within the nanojunctions that CB[n]s define. Through the enhanced Raman fingerprint, the real-time SERS-monitoring of a prototypical stilbene photoreaction is demonstrated. By choosing the appropriate CB[n] nanoreactor, selective photoisomerism or photodimerization is monitored in situ from within the AuNP-CB[n] nanogap.

Electrostatically Directed Self‐Assembly of Ultrathin Supramolecular Polymer Microcapsules

Supramolecular self-assembly offers routes to challenging architectures on the molecular and macroscopic scale. Coupled with microfluidics it has been used to make microcapsules—where a 2D sheet is shaped in 3D, encapsulating the volume within. In this paper, a versatile methodology to direct the accumulation of capsule-forming components to the droplet interface using electrostatic interactions is described. In this approach, charged copolymers are selectively partitioned to the microdroplet interface by a complementary charged surfactant for subsequent supramolecular cross-linking via cucurbit[8]uril. This dynamic assembly process is employed to selectively form both hollow, ultrathin microcapsules and solid microparticles from a single solution. The ability to dictate the distribution of a mixture of charged copolymers within the microdroplet, as demonstrated by the single-step fabrication of distinct core–shell microcapsules, gives access to a new generation of innovative self-assembled constructs.

Dynamically crosslinked materials via recognition of amino acids by cucurbit[8]uril

Hydrogels, an increasingly important class of material, have physical properties amenable to many potential uses, particularly in the biomedical area. Utilisation of hydrogels, however, relies not only on their mechanical properties but also on a favourable toxicity profile. Self assembly of polymers through naturally occurring and non-toxic units is therefore a very attractive option. The aromatic amino acids phenylalanine and tryptophan are two such molecular units that form 2 : 1 complexes with cucurbit[8]uril (CB[8]) with high binding equilibrium constants (Keq up to 1012 M-2). Herein, water soluble styrenic monomers were copolymerised with synthetically derived aromatic amino acid monomers of phenylalanine and tryptophan. The resulting polymers were shown to form dynamic and self-healing physically crosslinked hydrogels via recognition and binding of the amino acids to cucurbit[8]uril.

Microfluidic Droplet-Facilitated Hierarchical Assembly for Dual Cargo Loading and Synergistic Delivery

Bottom-up hierarchical assembly has emerged as an elaborate and energy-efficient strategy for the fabrication of smart materials. Herein, we present a hierarchical assembly process, whereby linear amphiphilic block copolymers are self-assembled into micelles, which in turn are accommodated at the interface of microfluidic droplets via cucurbit[8]uril-mediated host–guest chemistry to form supramolecular microcapsules. The monodisperse microcapsules can be used for simultaneous carriage of both organic (Nile Red) and aqueous-soluble (fluorescein isothiocyanate-dextran) cargo. Furthermore, the well-defined compartmentalized structure benefits from the dynamic nature of the supramolecular interaction and offers synergistic delivery of cargos with triggered release or through photocontrolled porosity. This demonstration of premeditated hierarchical assembly, where interactions from the molecular to microscale are designed, illustrates the power of this route toward accessing the next generation of functional materials and encapsulation strategies.

Microcapsule Buckling Triggered by Compression-Induced Interfacial Phase Change

There is an emerging trend toward the fabrication of microcapsules at liquid interfaces. In order to control the parameters of such capsules, the interfacial processes governing their formation must be understood. Here, poly(vinyl alcohol) films are assembled at the interface of water-in-oil microfluidic droplets. The polymer is cross-linked using cucurbit[8]uril ternary supramolecular complexes. It is shown that compression-induced phase change causes the onset of buckling in the interfacial film. On evaporative compression, the interfacial film both increases in density and thickens, until it reaches a critical density and a phase change occurs. We show that this increase in density can be simply related to the film Poisson ratio and area compression. This description captures fundamentals of many compressive interfacial phase changes and can also explain the observation of a fixed thickness-to-radius ratio at buckling, [Formula: see text].

Research data supporting "Microcapsule Buckling Triggered by Compression-Induced Interfacial Phase Change"

Numerical data from each graph are provided in tab-delimited text format. Uncropped versions of each image used are provided in png format. AFM data are enclosed in a zip folder containing mi format files. mi files can be opened with Gwyddion software which is freely available online. The files are labelled according to the relevant figure number. Refer to the manuscript and ESI for a description of the data.