Sequential Coalescence Enabled Two‐Step Microreactions in Triple‐Core Double‐Emulsion Droplets Triggered by an Electric Field

Advances in microfluidic emulsification have enabled the generation of exquisite multiple‐core droplets, which are promising structures to accommodate microreactions. An essential requirement for conducting reactions is the sequential coalescence of the multiple cores encapsulated within these droplets, therefore, mixing the reagents together in a controlled sequence. Here, a microfluidic approach is reported for the conduction of two‐step microreactions by electrically fusing three cores inside double‐emulsion droplets. Using a microcapillary glass device, monodisperse water‐in‐oil‐in‐water droplets are fabricated with three compartmented reagents encapsulated inside. An AC electric field is then applied through a polydimethylsiloxane chip to trigger the sequential mixing of the reagents, where the precise sequence is guaranteed by the discrepancy of the volume or conductivity of the inner cores. A two‐step reaction in each droplet is ensured by two times of core coalescence, which totally takes 20–40 s depending on varying conditions. The optimal parameters of the AC signal for the sequential fusion of the inner droplets are identified. Moreover, the capability of this technique is demonstrated by conducting an enzyme‐catalyzed reaction used for glucose detection with the double‐emulsion droplets. This technique should benefit a wide range of applications that require multistep reactions in micrometer scale.     

Microfluidic Designing Microgels Containing Highly Concentrated Gold Nanoparticles for SERS Analysis of Complex Fluids

Surface‐enhanced Raman scattering (SERS) is one of the most promising methods to detect small molecules for point‐of‐care analysis as it is rapid, nondestructive, label‐free, and applicable for aqueous samples. Here, microgels containing highly concentrated yet evenly dispersed gold nanoparticles are designed to provide SERS substrates that simultaneously achieve contamination‐free metal surfaces and high signal enhancement and reproducibility. With capillary microfluidic devices, water‐in‐oil‐in‐water (W/O/W) double‐emulsion drops are prepared to contain gold nanoparticles and hydrogel precursors in innermost drop. Under hypertonic condition, water is selectively pumped out from the innermost drops. Therefore, gold nanoparticles are gently concentrated without forming aggregates, which are then captured by hydrogel matrix. The resulting microgels have a concentration of gold nanoparticles ≈30 times higher and show Raman intensity two orders of magnitude higher than those with no enrichment. In addition, even distribution of gold nanoparticles results in uniform Raman intensity, providing high signal reproducibility. Moreover, as the matrix of the microgel serves as a molecular filter, large adhesive proteins are rejected, which enables the direct detection of small molecules dissolved in the protein solution. It is believed that this advanced SERS platform is useful for in situ detection of toxic molecules in complex mixtures such as biological fluids, foods, and cosmetics.     

Bioadhesive Polymersome for Localized and Sustained Drug Delivery at Pathological Sites with Harsh Enzymatic and Fluidic Environment via Supramolecular Host–Guest Complexation

Targeted and sustained delivery of drugs to diseased tissues/organs, where body fluid exchange and catabolic activity are substantial, is challenging due to the fast cleansing and degradation of the drugs by these harsh environmental factors. Herein, a multifunctional and bioadhesive polycaprolactone‐β‐cyclodextrin (PCL‐CD) polymersome is developed for localized and sustained co‐delivery of hydrophilic and hydrophobic drug molecules. This PCL‐CD polymersome affords multivalent crosslinking action via surface CD‐mediated host–guest interactions to generate a supramolecular hydrogel that exhibits evident shear thinning and efficient self‐healing behavior. The co‐delivery of small molecule and proteinaceous agents by the encapsulated PCL‐CD polymersomes enhances the differentiation of stem cells seeded in the hydrogel. Furthermore, the PCL‐CD polymersomes are capable of in situ grafting to biological tissues via host–guest complexation between surface CD and native guest groups in the tissue matrix both in vitro and in vivo, thereby effectively extending the retention of loaded cargo in the grafted tissue. It is further demonstrated that the co‐delivery of small molecule and proteinaceous drugs via PCL‐CD polymersomes averts cartilage degeneration in animal osteoarthritic (OA) knee joints, which are known for their biochemically harsh and fluidically dynamic environment.     

Ultrathin Shell Double Emulsion Templated Giant Unilamellar Lipid Vesicles with Controlled Microdomain Formation

A microfluidic approach is reported for the high‐throughput, continuous production of giant unilamellar vesicles (GUVs) using water‐in‐oil‐in‐water double emulsion drops as templates. Importantly, these emulsion drops have ultrathin shells; this minimizes the amount of residual solvent that remains trapped within the GUV membrane, overcoming a major limitation of typical microfluidic approaches for GUV fabrication. This approach enables the formation of microdomains, characterized by different lipid compositions and structures within the GUV membranes. This work therefore demonstrates a straightforward and versatile approach to GUV fabrication with precise control over the GUV size, lipid composition and the formation of microdomains within the GUV membrane.     

Microcapsules for Enhanced Cargo Retention and Diversity

Prevention of undesired leakage of encapsulated materials prior to triggered release presents a technological challenge for the practical application of microcapsule technologies in agriculture, drug delivery, and cosmetics. A microfluidic approach is reported to fabricate perfluoropolyether (PFPE)‐based microcapsules with a high core‐shell ratio that show enhanced retention of encapsulated actives. For the PFPE capsules, less than 2% leakage of encapsulated model compounds, including Allura Red and CaCl₂, over a four week trial period is observed. In addition, PFPE capsules allow cargo diversity by the fabrication of capsules with either a water‐in‐oil emulsion or an organic solvent as core. Capsules with a toluene‐based core begin a sustained release of hydrophobic model encapsulants immediately upon immersion in an organic continuous phase. The major contribution on the release kinetics stems from the toluene in the core. Furthermore, degradable silica particles are incorporated to confer porosity and functionality to the otherwise chemically inert PFPE‐based polymer shell. These results demonstrate the capability of PFPE capsules with large core–shell ratios to retain diverse sets of cargo for extended periods and make them valuable for controlled release applications that require a low residual footprint of the shell material.     

Osmocapsules for Direct Measurement of Osmotic Strength

Monodisperse microcapsules with ultra‐thin membranes are microfluidically designed to be highly sensitive to osmotic pressure, thereby providing a tool for the direct measurement of the osmotic strength. To make such osmocapsules, water‐in‐oil‐in‐water double‐emulsion drops with ultra‐thin shells are prepared as templates through emulsification of core–sheath biphasic flow in a capillary microfluidic device. When photocurable monomers are used as the oil phase, the osmocapsules are prepared by in‐situ photopolymerization of the monomers, resulting in semipermeable membranes with a relatively large ratio of membrane thickness to capsule radius, approximately 0.02. These osmocapsules are buckled by the outward flux of water when they are subjected to a positive osmotic pressure difference above 125 kPa. By contrast, evaporation‐induced consolidation of middle‐phase containing polymers enables the production of osmocapsules with a small ratio of membrane thickness to capsule radius of approximately 0.002. Such an ultra‐thin membrane with semi‐permeability makes the osmocapsules highly sensitive to osmotic pressure; a positive pressure as small as 12.5 kPa induces buckling of the capsules. By employing a set of distinct osmocapsules confining aqueous solutions with different osmotic strengths, the osmotic strength of unknown solutions can be estimated through observation of the capsules that are selectively buckled. This approach provides the efficient measurement of the osmotic strength using only a very small volume of liquid, thereby providing a useful alternative to other measurement methods which use complex setups. In addition, in‐vivo measurement of the osmotic strength can be potentially accomplished by implanting these biocompatible osmocapsules into tissue, which is difficult to achieve using conventional methods.     

Polymersome-loaded capsules for controlled release of DNA

The formation of a novel drug-delivery carrier for the controlled release of plasmid DNA that comprises layer-by-layer polymer capsules subcompartmentalized with pH-sensitive nanometer-sized polymersomes is reported. The amphiphilic diblock copolymer poly(oligoethylene glycol methacrylate)-block-poly(2-(diisopropylamino)ethyl methacrylate) forms polymersomes at physiological pH, but transitions to unimeric polymer chains upon acidification to cellular endocytic pH. These polymersomes can thus release an encapsulated payload in response to a change in pH from physiological to endocytic conditions. Multicomponent layer-by-layer capsules are formed by exploiting the ability of tannic acid to act as an efficient hydrogen-bond donor for both the polymersomes and poly(N-vinyl pyrrolidone) at physiological pH. These capsules show release of a plasmid DNA payload encapsulated within the polymersome subcompartments in response to changes in pH between physiological and endocytic conditions.     

Composite Microgels Created by Complexation between Polyvinyl Alcohol and Graphene Oxide in Compressed Double‐Emulsion Drops

Microgels, microparticles made of hydrogels, show fast diffusion kinetics and high reconfigurability while maintaining the advantages of hydrogels, being useful for various applications. Here, presented is a new microfluidic strategy for producing polymer‐graphene oxide (GO) composite microgels without chemical cues or a temperature swing for gelation. As a main component of microgels, polymers that are able to form hydrogen bonds, such as polyvinyl alcohol (PVA), are used. In the mixture of PVA and GO, GO is tethered by PVA through hydrogen bonding. When the mixture is rapidly concentrated in the core of double‐emulsion drops by osmotic‐pressure‐driven water pumping, PVA‐tethered GO sheets form a nematic phase with a planar alignment. In addition, the GO sheets are linked by additional hydrogen bonds, leading to a sol–gel transition. Therefore, the PVA–GO composite remains undissolved when it is directly exposed to water by oil‐shell rupture. These composite microgels can be also produced using poly(ethylene oxide) or poly(acrylic acid), instead of PVA. In addition, the microgels can be functionalized by incorporating other polymers in the presence of the hydrogel‐forming polymers. It is shown that the multicomponent microgels made from a mixture of polyacrylamide, PVA, and GO show an excellent adsorption capacity for impurities.     

Overcoming Concealment Effects of Targeting Moieties in the PEG Corona: Controlled Permeable Polymersomes Decorated with Folate‐Antennae for Selective Targeting of Tumor Cells

In the context of diligent efforts to improve the tumor targeting efficiency of drug carriers, a shape‐persistent polymersome which possess a pH‐tunable membrane as well as folate targeting antennae is reported. The membrane of such polymersomes behaves as gate which undergoes “on” and “off” switches in response to pH stimuli. Thus, polymersomes can effectively prohibit the premature release of chemotherapeutic agents such as doxorubicin in physiological conditions, but promote drug release once they are triggered in the acidified endosomal compartment. Importantly, the folate moieties are installed on the surface of polymersomes as protruding antennae by doping the polymersomes with folate‐terminated block copolymers designed to have longer PEG segments. Thereby, the folate moieties are freed from concealment and steric effects exerted by the dense PEG corona. The cellular uptake of the FA‐antennae polymersomes by tumor cells is significantly enhanced facilitated by the freely accessible folate antennae; however, the normal cells record a low level of cellular uptake due to the stealth property of the PEG corona. Overall, the excellent biocompatibility, controlled permeability, targeted internalization, as well as selective cytotoxicity of such polymersomes set up the basis for properly smart carrier for targeted drug delivery.     

Controlling Cellular Uptake by Surface Chemistry,Size, and Surface Topology at the Nanoscale

Cell cytosol and the different subcellular organelles house the most important biochemical processes that control cell functions. Effective delivery of bioactive agents within cells is expected to have an enormous impact on both gene therapy and the future development of new therapeutic and/or diagnostic strategies based on single‐cell–bioactive‐agent interactions. Herein a biomimetic nanovector is reported that is able to enter cells, escape from the complex endocytic pathway, and efficiently deliver actives within clinically relevant cells without perturbing their metabolic activity. This nanovector is based on the pH‐controlled self‐assembly of amphiphilic copolymers into nanometer‐sized vesicles (or polymersomes). The cellular‐uptake kinetics can be regulated by controlling the surface chemistry, the polymersome size, and the polymersome surface topology. The latter is controlled by the extent of polymer–polymer phase separation within the external envelope of the polymersome.     

An Investigation of PS‐b‐PEO Polymersomes for the Oral Treatment and Diagnosis of Hyperammonemia

Ammonia‐scavenging transmembrane pH‐gradient poly(styrene)‐b‐poly(ethylene oxide) polymersomes are investigated for the oral treatment and diagnosis of hyperammonemia, a condition associated with serious neurologic complications in patients with liver disease as well as in infants with urea cycle disorders. While these polymersomes are highly stable in simulated intestinal fluids at extreme bile salt and osmolality conditions, they unexpectedly do not reduce plasmatic ammonia levels in cirrhotic rats after oral dosing. Incubation in dietary fiber hydrogels mimicking the colonic environment suggests that the vesicles are probably destabilized during the dehydration of the intestinal chyme. The findings question the relevance of commonly used simulated intestinal fluids for studying vesicular stability. With the encapsulation of a pH‐sensitive dye in the polymersome core, the local pH increase upon ammonia influx could be exploited to assess the ammonia concentration in the plasma of healthy and cirrhotic rats as well as in other fluids. Due to its high sensitivity and selectivity, this polymersome‐based assay could prove useful in the monitoring of hyperammonemic patients and in other applications such as drug screening tests.     

Microfluidic Templated Multicompartment Microgels for 3D Encapsulation and Pairing of Single Cells

Controlled encapsulation and pairing of single cells within a confined 3D matrix can enable the replication of the highly ordered cellular structure of human tissues. Microgels with independently controlled compartments that can encapsulate cells within separately confined hydrogel matrices would provide precise control over the route of pairing single cells. Here, a one‐step microfluidic method is presented to generate monodisperse multicompartment microgels that can be used as a 3D matrix to pair single cells in a highly biocompatible manner. A method is presented to induce microgels formation on chip, followed by direct extraction of the microgels from oil phase, thereby avoiding prolonged exposure of the microgels to the oil. It is further demonstrated that by entrapping stem cells with niche cells within separate but adjacent compartments of the microgels, it can create complex stem cell niche microenvironments in a controlled manner, which can serve as a useful tool for the study of cell–cell interactions. This microfluidic technique represents a significant step toward high‐throughput single cells encapsulation and pairing for the study of intercellular communications at single cell level, which is of significant importance for cell biology, stem cell therapy, and tissue engineering.     

Efficient repairing effect of PEG based tri-block copolymer on mechanically damaged PC12 cells and isolated spinal cord

Membrane sealing effects of polymersomes made of tri-block copolymer, PEG-co-FA/SC-co-PEG, (PFSP) were studied on isolated spinal cord strips, PC12 cell lines and artificial bilayer following mechanical impact implemented by aneurism clip, sonication and electric shock, respectively. The homogeneity and size of PFSP, membrane permeability and cell viability were assessed by dynamic light scattering, LDH release and MTT assays. According to the results, the biocompatible, physico-chemical, size, surface charge and amphipathic nature of PFSP polymersome makes it an ideal macromolecule to rapidly reseal damaged membranes of cells in injured spinal cord as well as in culture medium. Compound action potentials recorded from intentionally damaged spinal cord strips incubated with PFSP showed restoration of neural excitability by 82.24 % and conduction velocity by 96.72 % after 5 min that monitored in real time. Thus, they triggered efficient instant and sustained sealing of membrane and reactivation of temporarily inactivated axons. Treatment of ultrasonically damaged PC12 cells by PFSP caused efficient cell membrane repair and led to their increased viability. The optimum effects of PFSP on stabilization and impermeabilizing of the lipid bilayer occurred at the same concentrations applied to the damaged cells and spinal cord fibers and was approved by restoration of membrane conductance and calcein release manifested by NanoDrop technique. The unique physico-chemical characteristics of novel polymersomes introduced here, make them capable to reorganize membrane lipid molecules, reseal the breaches and restore the hydrophobic insulation in spinal cord damaged cells. Thus, they might be considered in the clinical treatment of SCI at early stages.     

Monodisperse Emulsion Drop Microenvironments for Bacterial Biofilm Growth

In this work, microfluidic technology is used to rapidly create hundreds of thousands of monodisperse double and triple emulsion drops that serve as 3D microenvironments for the containment and growth of bacterial biofilms. The size of these drops, with diameters from tens to hundreds of micrometers, makes them amenable to rapid manipulation and analysis. This is demonstrated by using microscopy to visualize cellular differentiation of Bacillus subtilis biofilm communities within each drop and the bacterial biofilm microstructure. Biofilm growth is explored upon specific interfaces in double and triple emulsions and upon negative and positive radii of curvature. Biofilm attachment of matrix and flagella mutants is studied as well as biofilms of Pseudomonas aeruginosa. This is the first demonstration of biofilms grown in microscale emulsion drops, which serve as both templates and containers for biofilm growth and attachment. These microenvironments have the potential to transform existing high‐throughput screening methods for bacterial biofilms.     

Visualizing the Growth and Dynamics of Liquid‐Ordered Domains During Lipid Bilayer Folding in a Microfluidic Chip

A microfluidic platform enabling optical monitoring of bilayer lipid membrane formation by a new monolayer folding process is described. The thermoplastic chips integrate dried lipid films that are rehydrated by microfluidic perfusion, which enables delivery of lipid‐laden air bubbles across a membrane‐supporting aperture. As in traditional Montal–Mueller bilayer formation, lipid monolayers are delivered independently to each side of the aperture, thereby allowing asymmetric lipid composition in the resulting bilayer to be achieved. Confocal microscopy is used to image the monolayer folding process, and reveals the growth and dynamics of asymmetric liquid‐ordered domains during bilayer stabilization.     

Ultrathin Double‐Shell Capsules for High Performance Photon Upconversion

Triplet‐fusion‐based photon upconversion capsules with ultrathin double shells are developed through a single dripping instability in a microfluidic flow‐focusing device. An inner separation layer allows use of a brominated hydrocarbon oil‐based fluidic core, demonstrating significantly enhanced upconversion quantum yield. Furthermore, a perfluorinated photocurable monomer serves as a transparent shell phase with remote motion control through magnetic nanoparticle incorporation.     

Fluorescent liposome flow markers for microscale particle-image velocimetry

Unilamellar liposomes carrying both encapsulated and surface-immobilized fluorophores have been synthesized as novel fluorescent markers to image flow profiles in microfabricated structures. The unilamellar liposomes were made with phospholipids and cholesterol by extrusion through a polycarbonate membrane. They contained carboxyfluorescein in the aqueous core and fluorescein-labeled lipids in the bilayer to render them both a surface and volume fluorescer, maximizing their fluorescence intensity. The lipid composition was chosen to impart a net negative charge to liposomes to minimize self-aggregation as well as interaction with negatively charged glass surfaces of the channels. These liposomes were monodisperse (mean diameter 283 nm), neutrally buoyant, and hydrophilic and exhibited no adsorption on glass surfaces. Unlike polystyrene spheres, they were readily broken up by surfactants, thereby allowing for easy and complete removal from microfluidic channels. The fluorescent liposomes were used to investigate pressure-driven flow in an offset cross intersection in a microfluidic chip and provided images with excellent signal-to-noise ratio. A novel computational scheme that is particularly suitable for analyzing particle-image velocimeby data in micrometer-scale flow channels was employed to anabze the images. These liposomes are easily synthesized and can be custom-made for various applications to offer a broad range of surface and volume characteristics such as charge, size, and surface chemistry.     

Lipid bilayer formation by contacting monolayers in a microfluidic device for membrane protein analysis

Artificial planar lipid bilayers are a powerful tool for the functional study of membrane proteins, yet they have not been widely used due to their low stability and reproducibility. This paper describes an accessible method to form a planar lipid bilayer, simply by contacting two monolayers assembled at the interface between water and organic solvent in a microfluidic chip. The membrane of an organic solvent containing phospholipids at the interface was confirmed to be a bilayer by the capacitance measurement and by measuring the ion channel signal from reconstituted antibiotic peptides. We present two different designs for bilayer formation. One equips two circular wells connected, in which the water/solvent/water interface was formed by simply injecting a water droplet into each well. Another equips the cross-shaped microfluidic channel. In the latter design, formation of the interface at the sectional area was controlled by external syringe pumps. Both methods are extremely simple and reproducible, especially in microdevices, and will lead to automation and multiple bilayer formation for the high-throughput screening of membrane transport in physiological and pharmaceutical studies.     

单分散间苯二酚-甲醛气凝胶微球的制备工艺

采用T型微流体注射成型技术,以邻苯二甲酸二丁酯、液体石蜡和司班80为油相,间苯二酚/甲醛(RF)溶液为水相,经过溶胶-凝胶、溶剂交换、超临界干燥等过程制备了单分散RF气凝胶微球,并就制备过程中RF溶液与分散剂油相的选择、预聚时间、流速比、搅拌速率、固化温度等影响因素进行了初步讨论.当RF溶液质量分数为10%,60℃预聚1.5 h,间苯二酚与碳酸钠的物质的量之比为100,邻苯二甲酸二丁酯与液体石蜡的质量比为8:1,流速比控制在8～16,搅拌速率为65～90r/min,固化温度为35℃时,制备得到了RF乳液,其粒径分布系数小于2%.