Stimuli sensitive microcapsules with macroporous polymer shells

Porous microcapsules are of great interest in diverse applications, ranging from encapsulation for controlled release, to catalyst support to filtration and purification systems in analytical science. Here, we demonstrate a novel method to obtain porous microcapsules with polymer shells whose macroporosity and mechanical properties can be tuned within a wide range. Microcapsules are produced by microfluidics, using a co-flow flow-focusing glass capillary device to make water-oil-water (W/O/W) double emulsion templates. A mixture of acrylate monomers (glycidyl methacrylate and ethylene glycol dimethacrylate) and porogens (phthalate-based, alkanes or linear alcohols) is used as oil phase. Heterogeneous polymerization of the acrylate monomers leads to a biphasic structure in the capsule shell, in which a network of polymer beads is permeated by the liquid porogen. In the presence of hydrophobic porogens, the formation of a thin and tight polymer skin is observed on the inner and outer surfaces of the shell. This leads to sealed pores within the shell of the microcapsules, which can be used for the storage of chemicals in addition to the main encapsulant in the capsule core. As a proof of concept of such co-encapsulation of reactive compounds, we produced capsules loaded with separately stored monomers commonly used for two-components epoxy resins. Such capsules provide a rich platform for the design of solid adhesive and self-healing materials. Furthermore, the utilization of porogens with low boiling point, such as a short alkanes, leads to thermosensitive capsules that explosively release their content within seconds. Combining these capsules with magnetic particles heated by magnetic hyperthermia, we achieved a magnetic release of the capsules content within seconds and without over-heating the surrounding matrix. Incorporation of glycidyl methacrylate monomers results in polymer capsules with epoxy-functionalized surfaces, which can be further reacted with amine-based functional compounds. Exploiting such epoxy groups as anchors for grafting of sensitive polymers and for covalently attaching nanoparticles, we prepared multi-functional capsules with tailored shell structure and surface chemistries. Please click Additional Files below to see the full abstract

Strong Microcapsules with Macroporous Polymer Shells

Porous microcapsules have a broad range of applications that require a robust shell. We propose a new method to produce macroporous polymer capsules with controlled size, shell thickness, porosity and mechanical properties using co-flow flow-focusing glass capillary devices. The porous structure was investigated through SEM and the permeability through confocal microscopy. Compression tests on single capsules were performed. We obtained microcapsules with tailored permeability from open to close pores structures and able to withstand loads up to 150 g

Strong Dual-Compartment Microcapsules Loaded with High Cargo Contents

Compartmentalized microcapsules are useful for the release of multiple cargos in medicine, agriculture, and advanced responsive materials. Although several encapsulation strategies that involve more than one cargo have been proposed, dual- or multicompartment capsules with high cargo loadings and sufficient mechanical stability are rarely reported. Here, we propose a single-step emulsification route for the preparation of strong dual-compartment capsules that can host the main cargo in their core in combination with another liquid cargo stored within their thick shell. Capsules are produced through the polymerization of the middle oil phase of water–oil–water double emulsions made by microfluidics. Compartmentalization results from the phase separation of monomers within the middle phase of the double emulsion. We investigate the effect of such phase separation process on the microstructure and mechanical properties of the capsules and eventually illustrate the potential of this approach by creating thermosensitive capsules with programmable bursting temperature. The large variety of possible mixtures of monomers and cargos that can be added in the oil and aqueous phases of the double emulsion templates makes this encapsulation approach a promising route for the fabrication of robust microcapsules for on-demand release of multiple cargos

Strong Microcapsules with Permeable Porous Shells Made through Phase Separation in Double Emulsions

Microcapsules for controlled chemical release and uptake are important in many industrial applications but are often difficult to produce with the desired combination of high mechanical strength and high shell permeability. Using water–oil–water double emulsions made in microfluidic devices as templates, we developed a processing route to obtain mechanically robust microcapsules exhibiting a porous shell structure with controlled permeability. The porous shell consists of a network of interconnected polymer particles that are formed upon phase separation within the oil phase of the double emulsion. Porosity is generated by an inert diluent incorporated in the oil phase. The use of undecanol and butanol as inert diluents allows for the preparation of microcapsules covering a wide range of shell-porosity and force-at-break values. We found that the amount and chemical nature of the diluent influence the shell porous structure by changing the mechanism of phase separation that occurs during polymerization. In a proof-of-concept experiment, we demonstrate that the mechanically robust microcapsules prepared through this simple approach can be utilized for the on-demand release of small molecules using a pH change as exemplary chemical trigger