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Accurate control of monodisperse core-shell droplets generated in a microfluidic device has a broad range of applications in research and industry. This paper reports the experimental investigation of flow-focusing microfluidic devices capable of producing size-tuneable and monodisperse core-shell droplets. The dimension of the core-shell droplets was controlled passively by the channel geometry and the flow rate of the liquid phases. The results indicate that microchannel geometry is more significant than flow rates. The highly controllable core-shell droplets could be subsequently employed as a template for generating core-shell micropaticles with liquid core.Optical, electron microscopy and X-ray computed microtomography showed that the geometry of the core-shell droplets remains unchanged after solidification, drying and collection. The present study also looks at the thermal stability of core-shell particles depending on the particle size. The larger core-shell partcles with a thicker shell provide a higher resistance to heating at elevated temperature. The high degree of control with a flow-focusing microfluidic device makes this a promising approach for the encapsulation, storage, and delivery of lipophilic contents.

Core–shell microparticles containing an aqueous core have demonstrated their value for microencapsulation and drug delivery systems. The most important step in generating these uniquely structured microparticles is the formation of droplets and double emulsion. The droplet generator must meet the performance and reliability requirements, including accurate size control with tunability and monodispersity. Herein, we present a facile technique to generate surfactant-free core–shell droplets with an aqueous core in a microfluidic device. We demonstrate that the geometry of the core–shell droplets can be precisely adjusted by the flow rates of the droplet components. As the shell is polymerized after the formation of the core–shell droplets, the resulting solid microparticles ensure the encapsulation of the aqueous core and prevent undesired release. We then study experimentally and theoretically the behaviour of resultant microparticles under heating and compression. The microparticles demonstrate excellent stability under both thermal and mechanical loads. We show that the rupture force can be quantitatively predicted from the shell thickness relative to the outer shell radius. Experimental results and theoretical predictions confirm that the rupture force scales directly with the shell thickness. Graphical abstract

Core–shell particles are micro- or nanoparticles with solid, liquid, or gas cores encapsulated by protective solid shells. The unique composition of core and shell materials imparts smart properties on the particles. Core–shell particles are gaining increasing attention as tuneable and versatile carriers for pharmaceutical and biomedical applications including targeted drug delivery, controlled drug release, and biosensing. This review provides an overview of fabrication methods for core–shell particles followed by a brief discussion of their application and a detailed analysis of their manipulation including assembly, sorting, and triggered release. We compile current methodologies employed for manipulation of core–shell particles and demonstrate how existing methods of assembly and sorting micro/nanospheres can be adopted or modified for core–shell particles. Various triggered release approaches for diagnostics and drug delivery are also discussed in detail.

Digital droplet reactors have become a valuable tool for the analysis of single cells, organisms, or molecules by discretising reagents into picolitre or nanolitre volumes. However, deoxyribonucleic acid (DNA) based...