Uniform SiO2 microparticles containing controllable content of Na2SO4·10H2O against supercooling and phase separation are developed for efficient energy storage at mild temperatures. Na2SO4 solution with 3-aminopropyltriethoxysilane and silicone oil with tetraethylorthosilicate are emulsified into monodisperse water-in-oil (W/O) emulsions from microfluidics for template fabrication of the microparticles via hydrolysis and condensation. During the reaction process, Na2SO4 in the emulsion droplets crystallizes in the microparticles. Incorporation of sodium borate and sodium hexametaphosphate, combined with the confined distribution of Na2SO4·10H2O in the mesoporous microparticles, successfully avoids the phase separation of Na2SO4·10H2O and dramatically reduces its supercooling. This allows the microparticles to achieve repeatable energy storage/release property at mild temperatures for thermoregulation. Such a thermoregulating performance is demonstrated by incorporating the microparticles into a model house for repeatedly regulating its surface and inside temperatures. These microparticles show great potential for developing advanced materials for myriad fields such as energy, architecture, and healthcare.

A facile and flexible approach is developed for controllable fabrication of novel multiple-compartmental calcium alginate capsules from all-aqueous droplet templates with combined coextrusion minifluidic devices for isolated coencapsulation and synergistic release of diverse incompatible components. The multicompartmental capsules exhibit distinct compartments, each of which is covered by a distinct part of a heterogeneous shell. The volume and number of multiple compartments can be well-controlled by adjusting flow rates and device numbers for isolated and optimized encapsulation of different components, while the composition of different part of the heterogeneous shell can be individually tailored by changing the composition of droplet template for flexibly tuning the release behavior of each component. Two combined devices are first used to fabricate dual-compartmental capsules and then scaled up to fabricate more complex triple-compartmental capsules for coencapsulation. The synergistic release properties are demonstrated by using dual-compartmental capsules, which contain one-half shell with a constant release rate and the other half shell with a temperature-dependent release rate. Such a heterogeneous shell provides more flexibilities for synergistic release with controllable release sequence and release rates to achieve advanced and optimized synergistic efficacy. The multicompartmental capsules show high potential for applications such as drug codelivery, confined reactions, enzyme immobilizations, and cell cultures.Keywords: calcium alginate; coencapsulation; distinct shells; multicompartmental capsules; synergistic release

This work reports on an efficient microfluidic approach for continuous production of hollow Ca-alginate microfibers with controllable structures and functions. A coaxial microcapillary microfluidic device combined with a rotator is constructed to produce a cylindrical flow jet with four aqueous solutions as templates for continuous fabrication and collection of microfibers. A four-aqueous-phase flow jet with an intermediate buffer flow between the Ca2+-containing and alginate-containing flows is used as the template for microfiber fabrication. The buffer flow efficiently controls the diffusion of Ca2+ into the alginate-containing flow as well as the crosslinking reaction, thus ensuring the continuous fabrication of hollow Ca-alginate microfibers under relatively low flow rates without clogging of the microchannel. The structure of the hollow microfibers can be flexibly adjusted by changing the flow rates and device dimensions. Meanwhile, the continuous fabrication process of the microfibers allows flexible incorporation of a functional component into the sheath flow for functionalization and addition of active substances in the core flow for encapsulation. This is demonstrated by fabricating hollow Ca-alginate microfibers with a wall containing magnetic nanoparticles for magnetic functionalization and with hollow internals containing Chlorella pyrenoidosa cells for confined growth. This work provides an efficient strategy for continuous fabrication of functional hollow Ca-alginate microfibers with controllable structures and functions.

This paper reports on the continuous thermo-triggered one-to-one coalescence of controllable Pickering emulsion droplet pairs in microchannels, with thermo-responsive poly(N-isopropylacrylamide) (PNIPAM) microgels for stabilizing and destabilizing the droplet surface. Oil-in-water (O/W) emulsion droplets with distinct contents are periodically generated in the microfluidic device at temperatures below the volume phase transition temperature (VPTT) of PNIPAM microgels, thus the droplet surfaces are densely packed with hydrophilic and swollen PNIPAM microgels as stabilizers. With increasing the temperature higher than the VPTT, the PNIPAM microgels shrink and aggregate at the O/W interfaces, which expose the initially microgel-covered droplet surface for destabilization. Thus, when flowed into the heated expanded microchamber of the device, every two different droplets are paired and contact with each other for thermo-triggered coalescence, leading to fast mixing of the distinct contents. Such an on-chip thermo-triggered coalescence of controllable droplet pairs is highly attractive for the design and construction of novel droplet-based microsystems as microreactors and microdetectors for various applications such as bio/chemical synthesis, enzyme assays and DNA analysis.

Real-time online detection of trace threat analytes is critical for global sustainability, whereas the key challenge is how to efficiently convert and amplify analyte signals into simple readouts. Here we report an ultrasensitive microfluidic platform incorporated with smart microgel for real-time online detection of trace threat analytes. The microgel can swell responding to specific stimulus in flowing solution, resulting in efficient conversion of the stimulus signal into significantly amplified signal of flow-rate change; thus highly sensitive, fast, and selective detection can be achieved. We demonstrate this by incorporating ion-recognizable microgel for detecting trace Pb2+, and connecting our platform with pipelines of tap water and wastewater for real-time online Pb2+ detection to achieve timely pollution warning and terminating. This work provides a generalizable platform for incorporating myriad stimuli-responsive microgels to achieve ever-better performance for real-time online detection of various trace threat molecules, and may expand the scope of applications of detection techniques.

In this study, we report a facile approach for the fabrication of monodisperse hybrid alginate/protamine/silica (APSi) microcapsules with an ultrathin shell of submicron thickness as enzyme encapsulation systems for rapid enzymatic reactions. Monodisperse water-in-oil (W/O) emulsions, which have been generated in microfluidics, are used as templates for preparing APSi microcapsules via internal/external gelation and biosilicification. The microcapsules allow highly-efficient encapsulation of model actives bovine serum albumin (∼99%) during the fabrication process. The hybrid shell with an ultrathin thickness of ∼420 nm provides fast mass transfer for the encapsulated model enzyme laccase to undergo rapid reaction. Moreover, this rigid hybrid shell also endows the encapsulated laccase with excellent reusability and storage stability. These ultrathin-shelled APSi microcapsules show great potential as efficient encapsulation systems for enzymes and biomolecules for their rapid reactions, and as delivery systems for actives in biomedical applications.

A simple and flexible approach is developed for controllable fabrication of spider-silk-like microfibers with tunable magnetic spindle-knots from biocompatible calcium alginate for controlled 3D assembly and water collection. Liquid jet templates with volatile oil drops containing magnetic Fe3O4 nanoparticles are generated from microfluidics for fabricating spider-silk-like microfibers. The structure of jet templates can be precisely adjusted by simply changing the flow rates to tailor the structures of the resultant spider-silk-like microfibers. The microfibers can be well manipulated by external magnetic fields for controllably moving, and patterning and assembling into different 2D and 3D structures. Moreover, the dehydrated spider-silk-like microfibers, with magnetic spindle-knots for collecting water drops, can be controllably assembled into spider-web-like structures for excellent water collection. These spider-silk-like microfibers are promising as functional building blocks for engineering complex 3D scaffolds for water collection, cell culture, and tissue engineering.Keywords: biomimetic microfibers; magnetic assembly; microfluidics; template synthesis; water collection

A simple and versatile strategy is developed for one-step fabrication of uniform polymeric microparticles with controllable highly interconnected hierarchical porous structures. Monodisperse water-in-oil-in-water (W/O/W) emulsions, with methyl methacrylate, ethylene glycol dimethacrylate, and glycidyl methacrylate as the monomer-containing oil phase, are generated from microfluidics and used for constructing the microparticles. Due to the partially miscible property of oil/aqueous phases, the monodisperse W/O/W emulsions can deform into desired shapes depending on the packing structure of inner aqueous microdrops, and form aqueous nanodrops in the oil phase. The deformed W/O/W emulsions allow template syntheses of highly interconnected hierarchical porous microparticles with precisely and individually controlled pore size, porosity, functionality, and particle shape. The microparticles elaborately combine the advantages of enhanced mass transfer, large functional surface area, and flexibly tunable functionalities, providing an efficient strategy to physically and chemically achieve enhanced synergetic performances for extensive applications. This is demonstrated by using the microparticles for oil removal for water purification and protein adsorption for bioseparation. The method proposed in this study provides full versatility for fabrication of functional polymeric microparticles with controllable hierarchical porous structures for enhancing and even broadening their applications.Keywords: emulsions; hierarchical structures; interfaces; microparticles; porous materials;

In this study, we report on a simple and versatile plug-n-play microfluidic system that is fabricated from flexible assembly of glass-based flow-control modules for flexibly manipulating flows for versatile emulsion generation. The microfluidic system consists of three basic functional units: a flow-control module, a positioning groove, and a connection fastener. The flow-control module that is based on simple assembly of low-cost glass slides, coverslips, and glass capillaries provides excellent chemical resistance and optical properties, and easy wettability modification for flow manipulation. The flexible combination of the flow-control modules with 3D-printed positioning grooves and connection fasteners enables creation of versatile microfluidic systems for generating various higher-order multiple emulsions. The simple and reversible connection of the flow-control modules also allows easy disassembly of the microfluidic systems for further scale-up and functionalization. We demonstrate the scalability and controllability of flow manipulation by creating microfluidic systems from flexible assembly of flow-control modules for controllable generation of multiple emulsions from double emulsions to quadruple emulsions. Meanwhile, the flexible flow manipulation in the flow-control module provides advanced functions for improved control of the drop size, and for controllable generation of drops containing distinct components within multiple emulsions to extend the emulsion structure. Such modular microfluidic systems provide flexibility and versatility to flexibly manipulate micro-flows for enhanced and extended applications.

Here we report on a simple and flexible approach for continuous in situ fabrication of chitosan microfibers with controllable internals from tubular to peapod-like structures in microfluidics. Tubular and peapod-like jet templates can be generated at stable operation regions for template synthesis of chitosan microfibers with controllable tubular and peapod-like internals. The structure of each jet template can be precisely adjusted by simply changing the flow rates to tailor the structures of the resultant tubular and peapod-like chitosan microfibers. Both the tubular and peapod-like microfibers possess sufficient mechanical properties for further handling for biomedical applications. The tubular microfibers are used as biocompatible artificial vessels for transporting fluid, which is promising for delivering nutrition and blood for tissue engineering and cell culture. The peapod-like microfibers with controllable and separate oil cores can serve as multi-compartment systems for synergistic encapsulation of multiple drugs, showing great potential for developing drug-loaded medical patches for wound healing. The approach proposed in this study provides a facile and efficient strategy for controllable fabrication of microfibers with complex and well-tailored internals for biomedical applications.

Here we report a simple and versatile strategy for the in situ fabrication of nanogel-containing smart membranes in microchannels of microchips. The fabrication approach is demonstrated by the in situ formation of a chitosan membrane containing poly(N-isopropylacrylamide) (PNIPAM) nanogels in a microchannel of a microchip. The PNIPAM nanogels, that allow temperature- and ethanol-responsive swelling–shrinking volume transitions, serve as smart nanovalves for controlling the diffusional permeability of solutes across the membrane. Such self-regulation of the membrane permeability is investigated by using fluorescein isothiocyanate (FITC) as a tracer molecule. This approach provides a promising strategy for the in situ fabrication of versatile nanogel-containing smart membranes within microchips via simply changing the functional nanogels for developing micro-scale detectors, sensors, separators and controlled release systems.

Self-regulation of temperature in microchip systems is crucial for their applications in biomedical fields such as cell culture and biomolecule synthesis as well as those cases that require constant temperature conditions. Here we report on a simple and versatile approach for in situ fabrication of a smart hydrogel microvalve within a microchip for thermostatic control. The thermo-responsive hydrogel microvalve enables the “on–off” switch by sensing temperature fluctuations to control the fluid flux as well as the fluid heat exchange for self-regulation of the temperature at a constant range. Such temperature self-regulation is demonstrated by integrating the microvalve-incorporated microchip into the flow circulation loop of a micro-heat-exchanging system for thermostatic control. Moreover, the microvalve-incorporated microchip is employed for culturing cells under temperature self-regulation. The smart microvalve shows great potential as a temperature controller for applications that require thermostatic conditions. This approach offers a facile and flexible strategy for in situ fabricating hydrogel microvalves within microchips as chemostats and microreactors for biomedical applications.

Hydrogel-based microactuators that enable remote-controlled locomotion and fast Pb2+-response for micromanipulation in Pb2+-polluted microenvironment have been fabricated from quadruple-component double emulsions. The microactuators are Pb2+-responsive poly(N-isopropylacrylamide-co-benzo-18-crown-6-acrylamide) microgels, each with an eccentric magnetic core for magnetic manipulation and a hollow cavity for fast Pb2+-response. Micromanipulation of the microactuators is demonstrated by using them for preventing Pb2+-leakage from microchannel. The microactuators can be remotely and precisely transported to the Pb2+-leaking site under magnetic guide, and then clog the microchannel with Pb2+-responsive volume swelling to prevent flowing out of Pb2+-contaminated solution. The proposed microactuator structure provides a potential and novel model for developing multifunctional actuators and sensors, biomimetic soft microrobots, microelectro-mechanical systems and drug delivery systems.Keywords: magnetic materials; microactuators; microfluidics; microgels; micromanipulation; molecular recognition;

Hydrogel-based hollow microcapsules with good monodispersity and repeated glucose-response under physiological temperature and glucose concentration conditions have been fabricated by a simple emulsion-template approach. Double emulsions from microfluidic devices are used as templates to synthesize the monodisperse glucose-responsive microcapsules. In the poly(N-isopropylacrylamide-co-3-aminophenylboronic acid-co-acrylic acid) (P(NIPAM-co-AAPBA-co-AAc)) hydrogel shell of the microcapsules, the thermo-responsive PNIPAM network and the glucose-responsive AAPBA moiety are respectively used for actuation and glucose response, and the AAc moiety is used for adjusting the volume phase transition temperature of the shell. Glucose-responsive microcapsules prepared with 2.4 mol% AAc exhibit reversible and repeated swelling/shrinking response to glucose concentration changes within the physiological blood glucose concentration range (0.4–4.5 g L−1) at 37 °C. Rhodamine B and fluorescein-isothiocyanate-labeled insulin are used as model molecules and model drugs to demonstrate the potential application of the microcapsules for glucose-responsive controlled release. The microcapsules provide a promising and feasible model for developing glucose-responsive sensors and self-regulated delivery systems for diabetes and cancer therapy. Moreover, the microfluidic fabrication approach and research results presented here provide valuable guidance for the design and fabrication of monodisperse glucose-responsive microcapsules.

In this study, we report a facile approach for the fabrication of monodisperse hybrid alginate/protamine/silica (APSi) microcapsules with an ultrathin shell of submicron thickness as enzyme encapsulation systems for rapid enzymatic reactions. Monodisperse water-in-oil (W/O) emulsions, which have been generated in microfluidics, are used as templates for preparing APSi microcapsules via internal/external gelation and biosilicification. The microcapsules allow highly-efficient encapsulation of model actives bovine serum albumin (∼99%) during the fabrication process. The hybrid shell with an ultrathin thickness of ∼420 nm provides fast mass transfer for the encapsulated model enzyme laccase to undergo rapid reaction. Moreover, this rigid hybrid shell also endows the encapsulated laccase with excellent reusability and storage stability. These ultrathin-shelled APSi microcapsules show great potential as efficient encapsulation systems for enzymes and biomolecules for their rapid reactions, and as delivery systems for actives in biomedical applications.