From shaping to functionalization of micro-droplets and particles

Arrays of Bowl-Shaped Janus Particle Film with Structured Colors

Structural colors generated via total internal reflection (TIR) using nanostructure-free micro-concave shapes have garnered increasing attention. However, the application of large micro-concave structures for structural coloration remains limited. Herein, a flexibly tunable structural color film fabricated by casting polydimethylsiloxane (PDMS) on an array of large poly(glycidyl methacrylate) (PGMA) bowl-shaped particles is reported. The resultant film exhibits tunable red to green structural colors with changing observation angles. Moreover, the color can be further tailored by altering the shape of the film itself. The incorporation of the PDMS layer not only facilitates a shift in the locus of TIR from the bottom surface to the top concave surface of the particles, thereby enabling the generation of structural color, but also confers enhanced flexibility to the film. Further decoration with silver nanoparticles imparts antimicrobial properties, yielding a novel antimicrobial coating material with structural colors. The simple and cost-effective strategy for the production of structural color films provides potential applications in antimicrobial coatings, enabling accessible and customizable structural coloration using big-size micro-concave particles.

Recent Progress of Droplet Microfluidic Emulsification Based Synthesis of Functional Microparticles

The remarkable control function over the functional material formation process enabled by droplet microfluidic emulsification approaches can lead to the efficient and one-step encapsulation of active substances in microparticles, with the microparticle characteristics well regulated. In comparison to the conventional fabrication methods, droplet microfluidic technology can not only construct microparticles with various shapes, but also provide excellent templates, which enrich and expand the application fields of microparticles. For instance, intersection with disciplines in pharmacy, life sciences, and others, modifying the structure of microspheres and appending functional materials can be completed in the preparation of microparticles. The as-prepared polymer particles have great potential in a wide range of applications for chemical analysis, heavy metal adsorption, and detection. This review systematically introduces the devices and basic principles of particle preparation using droplet microfluidic technology and discusses the research of functional microparticle formation with high monodispersity, involving a plethora of types including spherical, nonspherical, and Janus type, as well as core-shell, hole-shell, and controllable multicompartment particles. Moreover, this review paper also exhibits a critical analysis of the current status and existing challenges, and outlook of the future development in the emerging fields has been discussed.

Static droplet array for the synthesis of nonspherical microparticles

We reported a manually operated static droplet array (SDA)-based device for the synthesis of nonspherical microparticles with different shapes. The improved SDA structure and reversible bonding between poly(dimethylsiloxane) (PDMS) were used in the device for the large-scale synthesis and rapid extraction of nonspherical microparticles. To understand the device physics, the effects of flow rate, SDA well size, and shape on droplet generation performances were explored. The results indicated that droplet generation in SDA structures was insensitive to the flow rate, and monodisperse droplets were generated by the SDA-based device through manually pushing the syringe. Finally, we integrated four kinds of SDA structures in one device and successfully realized the synthesis and extraction of nonspherical microparticles with different shapes and materials. Our SDA-based device offers numerous advantages, such as simple manual operation, low equipment cost, controllable microparticle shapes and sizes, and large-scale production. Thus, it holds the potential to be used as a flexible tool for the production of nonspherical microparticles.

Microfluidic Engineering of Crater-Terrain Hydrogel Microparticles: Toward Novel Cell Carriers

Fabrication and application of novel anisotropic microparticles are of wide interest. Herein, a new method for producing novel crater-terrain hydrogel microparticles is presented using a concept of droplet-aerosol impact and regional polymerization. The surface pattern of microparticles is similar to the widespread "crater" texture on the lunar surface and can be regulated by the impact morphology of aerosols on the droplet surface. Methodological applicability was demonstrated by producing ionic-cross-linked (alginate) and photo-cross-linked (poly(ethylene glycol) diacrylate, PEGDA) microparticles. Additionally, the crater-terrain microparticles (CTMs) can induce nonspecific protein absorption on their surface to acquire cell affinity, and they were exploited as cell carriers to load living cells. Cells could adhere and proliferate, and a special cellular adhesion fingerprint was observed on the novel cell carrier. Therefore, the scalable manufacturing method and biological potential make the engineered microparticles promising to open a new avenue for exploring cell-biomaterial crosstalk.

Recent Advances in Drug Delivery System Fabricated by Microfluidics for Disease Therapy

Traditional drug therapy faces challenges such as drug distribution throughout the body, rapid degradation and excretion, and extensive adverse reactions. In contrast, micro/nanoparticles can controllably deliver drugs to target sites to improve drug efficacy. Unlike traditional large-scale synthetic systems, microfluidics allows manipulation of fluids at the microscale and shows great potential in drug delivery and precision medicine. Well-designed microfluidic devices have been used to fabricate multifunctional drug carriers using stimuli-responsive materials. In this review, we first introduce the selection of materials and processing techniques for microfluidic devices. Then, various well-designed microfluidic chips are shown for the fabrication of multifunctional micro/nanoparticles as drug delivery vehicles. Finally, we describe the interaction of drugs with lymphatic vessels that are neglected in organs-on-chips. Overall, the accelerated development of microfluidics holds great potential for the clinical translation of micro/nanoparticle drug delivery systems for disease treatment.

Producing shape-engineered alginate particles using viscoplastic fluids

Non-spherical hydrogel particles are of fundamental interest and can find use in a variety of applications ranging from pharmaceuticals to biomedical to food. Here, we report a new method that leverages the yield stress property of viscoplastic fluids to synthesize shape-engineered alginate particles. By dripping an aqueous viscoplastic solution composed of sodium alginate and a yield-stress material into an ionic gelation bath, droplets are controllably deformed and crosslinked, producing a wide assortment of shapes. We find that by tuning the yield stress of the solution and the nozzle tip orientation, a range of shapes from symmetric and near-spherical, to asymmetric and anisotropic (e.g., egg-, rice grain-, arc-, ring-, snail shell-, tear-, and tadpole-like) can be produced. We explain our observations using scaling analysis of the forces exerted on the droplet at different stages of particle production. We show that the main factors that determine the degree of droplet deformation during bath entry and the final appearance of the alginate particles are the initial shape of the droplets, the timescales of the viscoplastic fluid relaxation versus the crosslinking reaction, and the physico-chemical properties of the yield-stress material.

Water promoted 9-fluorenylmethyloxycarbonyl detachment from amino acids in charged microdroplets

Aqueous microdroplets exhibit unique properties and can trigger reactions that do not occur in bulk solution. Herein, we have demonstrated that water, in microdroplets, can reduce the energy barrier for the lone H transfer of 9-fluorenylmethyloxycarbonyl and promote its detachment from the amino group. This strategy works on various amino acids and opens opportunities of aqueous microdroplets in triggering organic reactions.