High-Throughput Fabrication of Size-Controlled Pickering Emulsions, Colloidosomes, and Air-Coated Particles via Clog-Free Jetting of Suspensions.

Microcapsules with a liquid core and a solid shell composed of hydrophobic nanoparticles are broadly applied in food, pharmaceutics, and biotechnologies. For example, Pickering emulsions, colloidosomes, or antibubbles (droplets surrounded by air layers in water) enable controlled release of active agents, biocompatibility, and contact-less liquid transportation. However, producing controlled nanoparticle- or polymer-laden hydrophobic shells at scale is highly challenging, since bulk methods are polydisperse and microfluidic chips are prone to clogging and slow. Here, clog-free coating of an aqueous jet with silica nanoparticle suspensions with concentrations up to 10% (w/v), as well as high concentrations of polymers (30% (w/v) poly(lactic acid) (PLA)), is demonstrated, enabling continuous generation of microcapsules at flow rates up to 4 mL min-1 . Pickering emulsions are converted into capsules, providing hydrophobic shells consisting of nanoparticles for controlled release. As a highlight, the scalable fabrication of air-coated capsules (antibubbles) in the sub-millimeter range is demonstrated. The shell contains an air film that protects the liquid core for days yet enables ultrasound-induced release within 3 min. By enabling rapid fabrication of controlled Pickering emulsions, colloidosomes, antibubbles, and biodegradable capsules, jetting through a liquid layer (JetALL) provides a versatile platform for advanced applications in food, pharmacy, and life science.

Dynamic mechanical analysis of suspended soft bodies via hydraulic force spectroscopy.

The rheological characterization of soft suspended bodies, such as cells, organoids, or synthetic microstructures, is particularly challenging, even with state-of-the-art methods (e.g. atomic force microscopy, AFM). Providing well-defined boundary conditions for modeling typically requires fixating the sample on a substrate, which is a delicate and time-consuming procedure. Moreover, it needs to be tuned for each chemistry and geometry. Here, we validate a novel technique, called hydraulic force spectroscopy (HFS), against AFM dynamic indentation taken as the gold standard. Combining experimental data with finite element modeling, we show that HFS gives results comparable to AFM microrheology over multiple decades, while obviating any sample preparation requirements.

Continuous High-Throughput Fabrication of Architected Micromaterials via In-Air Photopolymerization.

Recent advances in optical coding, drug delivery, diagnostics, tissue engineering, shear-induced gelation, and functionally engineered rheology crucially depend on microparticles and microfibers with tunable shape, size, and composition. However, scalable manufacturing of the required complex micromaterials remains a long-standing challenge. Here in-air polymerization of liquid jets is demonstrated as a novel platform to produce microparticles and microfibers with tunable size, shape, and composition at high throughput (>100 mL h-1 per nozzle). The polymerization kinetics is quantitatively investigated and modeled as a function of the ink composition, the UV light intensity, and the velocity of the liquid jet, enabling engineering of complex micromaterials in jetting regimes. The size, morphology, and local chemistry of micromaterials are independently controlled, as highlighted by producing micromaterials using 5 different photopolymers as well as multi-material composites. Simultaneous optimization of these control parameters yields rapid fabrication of stimuli-responsive Janus fibers that function as soft actuators. Finally, in-air photopolymerization enables control over the curvature of printed droplets, as highlighted by high-throughput printing of microlenses with tunable focal distance. The combination of rapid processing and tunability in composition and architecture opens a new route toward applications of tailored micromaterials in soft matter, medicine, pharmacy, and optics.

Directional pumping of water and oil microdroplets on slippery surface.

Transporting water and oil microdroplets is important for applications ranging from water harvesting to biomedical analysis but remains a great challenge. This is due to the amplified contact angle hysteresis and insufficient driving force in the micrometer scale, especially for low-surface energy oil droplets. Coalescence of neighboring droplets, which releases vast additional surface energy, was often required, but its relatively uncontrollable nature brings uncertainties to the droplet motion, and the methodology is not applicable to single droplets. Here we introduce a strategy based on slippery surface with immobilized lubricant menisci to directionally transport microdroplets. By simply mounting hydrogel dots on slippery surface, the raised menisci remotely pump microdroplets via capillary force with high efficiency, regardless of droplet size or surface energy. By proof-of-concept experiments, we demonstrate that our method allows for highly efficient water droplet collection and highly sensitive biomedical analyte detection.

Up-to-date vaccine delivery systems: robust immunity elicited by multifarious nanomaterials upon administration through diverse routes.

In this review, we summarize the recent design strategies (2015-present) of nanomaterial-based vaccine delivery systems via multiple routes to induce robust protective immunity. The selected topics are focused on the novel design strategies of nanomaterial carriers for vaccine delivery. Inspired by recent advances, we also briefly introduce the emerging administration routes that may give rise to synergistic immune effects with advanced delivery systems. Ultimately, we present the existing challenges and survey the prospective development of various nanoparticle vaccine delivery systems.

Self-Healable Organogel Nanocomposite with Angle-Independent Structural Colors.

Structural colors have profound implications in the fields of pigments, displays and sensors, but none of the current non-iridescent photonic materials can restore their functions after mechanical damage. Herein, we report the first self-healable organogel nanocomposites with angle-independent structural colors. The organogel nanocomposites were prepared through the co-assembly of oleophilic silica nanoparticles, silicone-based supramolecular gels, and carbon black. The organogel system enables amorphous aggregation of silica nanoparticles and the angle-independent structural colors in the nanocomposites. Moreover, the hydrogen bonding in the supramolecular gel provides self-healing ability to the system, and the structural colored films obtained could heal themselves in tens of seconds to restore storage modulus, structural color, and surface slipperiness from mechanical cuts or shear failure repeatedly.

Development of "Liquid-like" Copolymer Nanocoatings for Reactive Oil-Repellent Surface.

Here, we describe a simple method to prepare oil-repellent surfaces with inherent reactivity. Liquid-like copolymers with pendant reactive groups are covalently immobilized onto substrates via a sequential layer-by-layer method. The stable and transparent nanocoatings showed oil repellency to a broad range of organic liquids even in the presence of reactive sites. Functional molecules could be covalently immobilized onto the oil-repellent surfaces. Moreover, the liquid repellency can be maintained or finely tailored after post-chemical modification via synergically tailoring the film thickness, selection of capping molecules, and labeling degree of the capping molecules. Oil-repellent surfaces that are capable of post-functionalization would have technical implications in surface coatings, membrane separation, and biomedical and analytical technologies.

Adhesion of Microdroplets on Water-Repellent Surfaces toward the Prevention of Surface Fouling and Pathogen Spreading by Respiratory Droplets.

Biofouling caused by the adhesion of respiratory microdroplets generated in sneezing and coughing plays an important role in the spread of many infectious diseases. Although water-repellent surfaces are widely used for the long-term repellency of aqueous solutions, their repellency to pathogen-containing microdroplets is elusive. In this work, microdroplets from picoliter to nanoliter were successfully generated in a controlled manner to mimic the exhaled microdroplets in sneezing and coughing, which allowed us to evaluate the adhesion of microdroplets on both superhydrophobic and lubricant-infused "slippery" surfaces for the first time. The impact and retention of water microdroplets on the two water-repellent surfaces are compared and investigated. Microdroplet-mediated surface biofouling and pathogen transmission were also demonstrated. Our results suggested that the adhesion of microdroplets should be duly considered in the design and application of water-repellent surfaces on biofouling prevention.

Fabrication of Transparent Multilayer Circuits by Inkjet Printing.

Conductive microcables embedded in a transparent film are fabricated by inkjet printing silver-nanoparticle ink into a liquid poly(dimethylsiloxane) (PDMS) precursor substrate. By controlling the spreading of the ink droplet and the rheological properties of the liquid substrate, transparent multilayer circuits composed of high-resolution embedded cables are achieved using a commercial inkjet printer. This facile strategy provides a new avenue for inkjet printing of highly integrated and transparent electronics.

Fabrication of Bendable Circuits on a Polydimethylsiloxane (PDMS) Surface by Inkjet Printing Semi-Wrapped Structures.

In this work, an effective method was developed to fabricate bendable circuits on a polydimethylsiloxane (PDMS) surface by inkjet printing semi-wrapped structures. It is demonstrated that the precured PDMS liquid film could influence the depositing morphology of coalesced silver precursor inkjet droplets. Accordingly, continuous and uniform lines with a semi-wrapped structure were fabricated on the PDMS surface. When the printed silver precursor was reduced to Ag nanoparticles, the fabricated conductive film exhibited good transparency and high bendability. This work presented a facile way to fabricate flexible patterns on a PDMS surface without any complicated modification or special equipment. Meanwhile, an in situ hydrazine reduction of Ag has been reported using the vapor phase method in the fabricating process.

Patterning fluorescent quantum dot nanocomposites by reactive inkjet printing.

Fluorescent quantum dot nanocomposites, including polymer and photonic crystal quantum dots, have been fabricated by reactive inkjet printing. This reactive inkjet printing method has the potential to be broadened to fabrication of other functional nanomaterials, which will find promising applications in optoelectronic devices.