Tunable Structural Coloration in Eccentric Water-in-Oil-in-Water Droplets.

Structural colors show diverse advantages such as fade resistance, eco-friendliness, iridescence, and high saturation in comparison with chemical pigments. In this paper, we show tunable structural coloration in colorless water-in-oil-in-water double emulsion droplets via total internal reflection and interference at the microscale concave interfaces. Through experimental work and simulations, we demonstrate that the shell thickness and the eccentricity of the core-shell structures are key to the successful formation of iridescent structural colors. Only eccentric thin-shell water-in-oil-in-water droplets show structural colors. Importantly, structural colors based on water-oil interfaces are readily responsive to a variety of environmental stimuli, such as osmotic pressure, temperature, magnetic fields, and light composition. This work highlights an alternative structural coloration that expands the applications of droplet-based structural colors to aqueous systems.

Controllable Fabrication of Highly Uniform Sub-10 nm Nanoparticles from Spontaneous Confined Nanoemulsification.

Sub-10 nm nanoparticles are known to exhibit extraordinary size-dependent properties for wide applications. Many approaches have been developed for synthesizing sub-10 nm inorganic nanoparticles, but the fabrication of sub-10 nm polymeric nanoparticles is still challenging. Here, a scalable, spontaneous confined nanoemulsification strategy that produces uniform sub-10 nm nanodroplets for template synthesis of sub-10 nm polymeric nanoparticles is proposed. This strategy introduces a high-concentration interfacial reaction to create overpopulated surfactants that are insoluble at the droplet surface. These overpopulated surfactants act as barriers, resulting in highly accumulated surfactants inside the droplet via a confined reaction. These surfactants exhibit significantly changed packing geometry, solubility, and interfacial activity to enhance the molecular-level impact on interfacial instability for creating sub-10 nm nanoemulsions via self-burst nanoemulsification. Using the nanodroplets as templates, the fabrication of uniform sub-10 nm polymeric nanoparticles, as small as 3.5 nm, made from biocompatible polymers and capable of efficient drug encapsulation is demonstrated. This work opens up brand-new opportunities to easily create sub-10 nm nanoemulsions and advanced ultrasmall functional nanoparticles.

Thermochromic Photonic Crystal Microspheres with Uniform Color Display and Wide Coloration Range.

Thermochromic microspheres based on poly(N-isopropylacrylamide) attract much attention in detection and sensor due to the noticeable color response and fast response rate. However, some issues such as uneven color display and narrow coloration range still limit their practical applications. Herein, novel thermochromic microspheres with homogeneous color displays and wide thermochromic range are designed by combining the microfluidic technology with the magnetically-induced self-assembly technique and copolymerizing acrylamide (AM) with N-isopropylacrylamide. The photonic crystal structure with especially even colors is fast and conveniently constructed by magnetic assembly. The addition of AM makes the microspheres more hydrophilic and thus leading to a broader coloration range. The relationship between the structural color display and both the microstructures of photonic crystals and the thermo-responsive properties of gel matrix are elucidated. The detectable temperature of microspheres rises to as high as 60°C, and displays bright iridescent color variations from orange to blue-violet in the heating process. Importantly, their shrinking or swelling equilibrium can be reached in 80 and 105 s. Such microspheres are successfully used to visually indicate the appropriate temperature of enzymatic reaction, and have great potential in practical applications such as visual temperature detection and efficiency monitoring of chemical reactions.

Exploration of the Adsorption Kinetics of Surfactants at the Water-Oil Interface via Grand-Canonical Molecular Dynamics Simulations.

It is well-known that surfactants tend to aggregate into clusters or micelles in aqueous solutions due to their special structures, and it is difficult for the surfactant molecules involved in the aggregation to move spontaneously to the oil-water interface. In this article, we developed a new grand-canonical molecular dynamics (GCMD) model to predict the saturated adsorption amount of surfactant with constant concentration of surfactant molecules in the bulk phase, which can prevent surfactants aggregating in the bulk phase and get the atomic details of the interfacial structural change with increase of the adsorption amount through a single GCMD run. The adsorption of anionic surfactant sodium dodecyl sulfate (SDS) at the heptane-water interface was studied to validate the model. The saturated adsorption amount obtained from the GCMD simulation is consistent with the experimental results. The adsorption kinetics of SDS molecules during the simulation can be divided into three stages: linear adsorption stage, transition adsorption stage, and dynamic equilibrium stage. We also carried out equilibrium molecular dynamics (EMD) simulations to compare with GCMD simulation. This GCMD model can effectively reduce the simulation time with correct prediction of the interfacial saturation adsorption. We believe the GCMD method could be especially helpful for the computational study of surfactant adsorption under complex environments or emulsion systems with the adsorption of multiple types of surfactants.

Pseudo Polyampholytes with Sensitively Ion-Responsive Conformational Transition Based on Positively Charged Host-Guest Complexes.

Biological polyampholytes are ubiquitous in living organisms with primary functions including serving as transporters for moving chemical molecular species across the cell membranes. Synthetic amphoteric macromolecules that can change their phase states depending on the environment to simulate some properties of natural polyampholytes are of great interest. Here, the implementation of synthetic pseudo polymeric ampholytes is explored with ion-recognition-triggered conformational change. The phase transition behaviors of the ion-recognition-creative polyampholytes that contain deprotonated carboxylic acid groups as negative charges and 18-crown-6 units for forming positively charged host-guest complexes are systematically investigated. The ion-recognition-triggered phase transition behaviors of pseudo polyampholytes significantly depend on cation species and concentrations. Only those specific ions such as K+ , Ba2+ , Sr2+ and Pb2+ ions that can form 1:1 host-guest complexes with 18-crown-6 units in polymers enable control over conformational change like that of traditional pH-dependent polyampholytes. By regulating the content of carboxylic acid groups to match the content of ion-recognized positive charges provided by the host-guest complexes, the pseudo polyampholytes are more sensitive to the recognizable cations. Such ion-recognition-triggered amphoteric characteristics make the pseudo polyampholytes act like biological proteins, nucleic acids, and enzymes as molecular transporters, genetic code storage, and biocatalysts in artificial systems.

Magnetically Assembled Photonic Crystal Gels with Wide Thermochromic Range and High Sensitivity.

Thermochromic poly(N-isopropyl acrylamide) (PNIPAM) photonic crystal gels based on 1D magnetically assembling colloidal nanocrystal clusters have attracted much attention due to its convenient preparation process, striking color response, and good mechanical strength. However, there remain challenges to broaden the thermochromic range and improve the sensitivity for their iridescent color display. Here, a PNIPAM photonic gel with wide thermochromic range and high sensitivity is prepared by using four-arm star poly(ethylene glycol) acrylamide (PEGAAm) as cross-linker at appropriately reduced magnetic field strength as well as cross-linker content. PEGAAm improves the homogeneity of the microstructure in PNIPAM photonic gel and thus maintains the structure colors at a wide temperature range from room temperature to 44 °C. The reduced magnetic field strength of 70 Gs and low cross-linker content (the molar ratio of monomer to cross-linker of 300:1) lead to a large initial lattice spacing of the photonic gel and thus wide diffraction wavelength migration of 194 nm. This optimized PNIPAM gel exhibits vivid iridescent colors from orange-red to indigo blue as temperature increases from 20 to 44 °C with satisfactory repeatability. Therefore, it may be an ideal candidate for temperature sensors and displays with utility and accuracy such as low-temperature burns.

Magnetic hierarchical porous SiO2 microparticles from droplet microfluidics for water decontamination.

A simple and flexible strategy based on droplet microfluidics is developed for controllable fabrication of uniform magnetic SiO2 microparticles with highly-interconnected hierarchical porous structures for enhanced water decontamination. Uniform precursor water droplets containing surfactants and homogenized fine oil droplets with a relatively high volume ratio are generated from microfluidics as templates for microparticle synthesis via hydrolysis/condensation reaction. The SiO2 microparticles possess hierarchical porous structures, containing both mesopores with size of several nanometers, and well-controlled and highly-interconnected macropores with size of hundreds of nanometers. The SiO2 microparticles synergistically integrate fast mass transfer and large functional surface area for enhanced adsorption. To demonstrate the enhanced adsorption performances for organic dyes and toxic heavy metal ions, the microparticles are respectively used for removal of methylene blue in water, and modified with thiol-groups for removal of Pb2+ ions in water. Meanwhile, the microparticles can be easily recycled by magnetic field for reuse.

Ultrasensitive microchip based on smart microgel for real-time online detection of trace threat analytes.

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 Pb(2+), and connecting our platform with pipelines of tap water and wastewater for real-time online Pb(2+) 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.

[Applications of marine-derived chitosan and alginates in biomedicine].

Marine-derived biopolymers are excellent raw materials for biomedical products due to their abundant resources, good biocompatibility, low cost and other unique functions. Marine-derived biomaterials become a major branch of biomedical industry and possess promising development prospects since the industry is in line with the trend of "green industry and low-carbon economy". Chitosan and alginates are the most commonly commercialized marine-derived biomaterials and have exhibited great potential in biomedical applications such as wound dressing, dental materials, antibacterial treatment, drug delivery and tissue engineering. This review focuses on the properties and applications of chitosan and alginates in biomedicine.

Acyclic Janus-AT Nucleoside Host Channels Precisely Lock Water into Single-File Wires with Local Rotational Flexibility.

Confining polar water molecules to particular geometries demands sophisticated intermolecular interactions, and not many small synthetic molecules have accomplished such a task. Herein, regioisomeric acyclic Janus-AT nucleosides (1 and 2), with a self-complementary fused genetic alphabet and conformationally flexible side chains, have been selectively synthesized. 1 and 2 adopt disparate base-pair motifs from the π-π stacked hydrophobic base moieties and distinct hydrogen bond (HB) interconnections from the hydrophilic sugar residues, which in turn lead to divergent, intricate intermolecular interaction networks with different capacities to confine water molecules. Under the precise control of the host framework of the N8 -regioisomer, separate ordered single-file water wires can be locked through special three-HB clamps into unique inter- and intra-wire geometrical alignments. Localized dynamic synchronized rotations within the fixed framework coordinated by both the host hydroxy groups and guest water molecules were observed in a temperature-induced reversible single-crystal-to-single-crystal transition (SCSCT).

A Novel Thermoresponsive Catalytic Membrane with Multiscale Pores Prepared via Vapor-Induced Phase Separation.

A novel thermoresponsive catalytic polyethersulfone membrane with multiscale pores is developed by constructing silver nanoparticles (Ag NPs) loaded poly(N-isopropylacrylamide) (PNIPAM) nanogels on pore walls of cellular pores as thermoresponsive gates and catalysts via vapor-induced phase separation. The Ag NPs are stably immobilized on the PNIPAM nanogels by an in situ reduction method based on the versatile adhesion and reduction properties of polydopamine. The micrometer cellular pores decorated with Ag NPs loaded PNIPAM nanogels are formed throughout the membrane and act as numerous microreactors with a large pore surface. The proposed membrane exhibits both satisfactory thermoresponsive characteristics and stable catalytic properties. The effects of operation temperature and reactant concentration of feed solution on the catalytic properties are investigated systematically. The results show that the apparent kinetic rate constant of catalytic reduction of 4-nitrophenol (4-NP) in water by reductant sodium borohydride (NaBH4 ), is ranging from 3.7 to 37.9 min-1 at temperatures from 20 to 45 ºC and the molar ratio of NaBH4 to 4-NP from 100:1 to 500:1. When the reactant concentration in feed solution fluctuates, the permeability or throughput of the membrane is simply adjusted by virtue of the thermoresponsive characteristics of membranes to achieve high catalytic conversion of reactant.

A Simple Device Based on Smart Hollow Microgels for Facile Detection of Trace Lead(II) Ions.

A simple device, which is equipped with a non-woven fabric filter medium immobilized with ion-recognizable smart hollow microgels, is developed for facile detection of trace lead(II) ions (Pb2+ ). The ion-recognizable smart microgels are made of poly(N-isopropylacrylamide-co-benzo-18-crown-6-acrylamide) (PNB), in which the 18-crown-6 groups act as the sensors of Pb2+ and the N-isopropylacrylamide groups act as the actuators. The PNB hollow microgels can isothermally change from a shrunk state to a swollen state in response to recognizing Pb2+ in the aqueous environment due to the electrostatic repulsion among the charged 18-crown-6/Pb2+ complex groups and the enhancement of hydrophilicity of the microgels. Due to the hollow structures, the PNB microgels show remarkable isothermal swelling ratio. Thus, the flux of solution pass through the non-woven fabric filter medium decreases significantly because of the remarkable reduction in the space for liquid flowing upon recognizing Pb2+ . The Pb2+ concentration can be detected quantitatively by simply and easily measuring the change of solution flux using the proposed device, which is operated without external power supply or spectroscopic measurements. The strategy proposed in this study provides a promising method for facile detection of trace Pb2+ in aqueous environments.

Controllable Microfluidic Fabrication of Microstructured Materials from Nonspherical Particles to Helices.

This work reports on a facile and flexible strategy based on the deformation of encapsulated droplets in fiber-like polymeric matrices for template synthesis of controllable microstructured materials from nonspherical microparticles to complex 3D helices. Monodisperse droplets generated from microfluidics are encapsulated into crosslinked polymeric networks via an interfacial crosslinking reaction in microchannel to in situ produce the droplet-containing, fiber-like matrices. By stretching and twining the dried fiber-like matrices, the encapsulated droplets can be flexibly engineered into versatile shapes for template synthesis of controllable nonspherical microparticles and helices. Moreover, magnetic helices can be fabricated by simply dispersing magnetic Fe3 O4 nanoparticles in the droplets to achieve rotational and translational motion under a rotated magnetic field. This work provides a simple and versatile strategy for the template synthesis of advanced functional microstructured materials with flexible shapes.

Stimuli-responsive smart gating membranes.

Membranes are playing paramount roles in the sustainable development of myriad fields such as energy, environmental and resource management, and human health. However, the unalterable pore size and surface properties of traditional porous membranes restrict their efficient applications. The performances of traditional membranes will be weakened upon unavoidable membrane fouling, and they cannot be applied to cases where self-regulated permeability and selectivity are required. Inspired by natural cell membranes with stimuli-responsive channels, artificial stimuli-responsive smart gating membranes are developed by chemically/physically incorporating stimuli-responsive materials as functional gates into traditional porous membranes, to provide advanced functions and enhanced performances for breaking the bottlenecks of traditional membrane technologies. Smart gating membranes, integrating the advantages of traditional porous membrane substrates and smart functional gates, can self-regulate their permeability and selectivity via the flexible adjustment of pore sizes and surface properties based on the "open/close" switch of the smart gates in response to environmental stimuli. This tutorial review summarizes the recent developments in stimuli-responsive smart gating membranes, including the design strategies and the fabrication strategies that are based on the introduction of the stimuli-responsive gates after or during membrane formation, and the positively and negatively responsive gating models of versatile stimuli-responsive smart gating membranes, as well as the advanced applications of smart gating membranes for regulating substance concentration in reactors, controlling the release rate of drugs, separating active molecules based on size or affinity, and the self-cleaning of membrane surfaces. With self-regulated membrane performances, smart gating membranes show great power for use in global sustainable development.

Functional polymeric microparticles engineered from controllable microfluidic emulsions.

Functional polymeric microparticles with typical sizes of 1-1000 µm have received considerable attention for many applications. Especially in biomedical fields, polymeric microparticles with advanced functions such as targeted delivery, controlled encapsulation, or "capture and release" show great importance as delivery systems for active molecules and drugs, as imaging agents for analytics and diagnostics, as microreactors for confined bioreactions, and more. Generally, the functions of these microparticles rely on both their structures and the properties of their component materials. Thus, creating unique structures from functional materials provides an important strategy for developing advanced functional polymeric microparticles. Several methods, such as dispersion polymerization, precipitation polymerization, copolymer self-assembly, and phase-separated polymer precipitation can be used to make functional microparticles, but each has limitations, for example, their limited control over the particle size and structure. Using emulsions as templates, however, allows precise control over the size, shape, composition, and structure of the resulting microparticles by tuning those of the emulsions via specific emulsification techniques. Microfluidic methods offer excellent control of emulsion droplets, thereby providing a powerful platform for continuous, reproducible, scalable production of polymeric microparticles with unprecedented control over their monodispersity, structures, and compositions. This approach provides broad opportunities for producing polymeric microparticles with novel structure-property combinations and elaborately designed functions. In this Account, we highlight recent efforts in microfluidic fabrication of advanced polymeric microparticles with well-designed functions for potential biomedical applications, and we describe the development of microfluidic techniques for producing monodisperse and versatile emulsion templates. We begin by describing microparticles made from single emulsions and then describe those from complex multiple emulsions, showing how the resulting microparticles combine novel structures and material properties to achieve their advanced functions. Monodisperse emulsions enable production of highly uniform microparticles of desired sizes to achieve programmed release rates and passive targeting for drug delivery and diagnostic imaging. Phase-separated multiple emulsions allow combination of a variety of functional materials to generate compartmental microparticles including hollow, core-shell, multicore-shell, and hole-shell structures for controlled encapsulation and release, selective capture, and confined bioreaction. We envision that the versatility of microfluidics for microparticle synthesis could open new frontiers and provide promising and exciting opportunities for fabricating new functional microparticles with broad implications for myriad fields.

Monodisperse and fast-responsive poly(N-isopropylacrylamide) microgels with open-celled porous structure.

A simple and efficient method is developed to fabricate monodisperse and fast-responsive poly(N-isopropylacrylamide) (PNIPAM) microgels with open-celled porous structure. First, numerous fine oil droplets are fabricated by homogeneous emulsification method and are then evenly dispersed inside monodisperse PNIPAM microgels as porogens via the combination of microfluidic emulsification and UV-initiated polymerization methods. Subsequently, the embedded fine oil droplets inside the PNIPAM microgels are squeezed out upon stimuli-induced rapid volume shrinkage of the microgels; as a result, a spongelike open-celled porous structure is formed inside the PNIPAM microgels. The open-celled porous structure provides numerous interconnected free channels for the water transferring convectively inward or outward during the volume phase transition process of PNIPAM microgels; therefore, the response rates of the PNIPAM microgels with open-celled porous structure are much faster than that of the normal ones in both thermo-responsive shrinking and swelling processes. Because of the fast-responsive characteristics, the microgels with open-celled porous structure will provide ever better performances in their myriad applications, such as microsensors, microactuators, microvalves, and so on.

Competitive molecular-/ion-recognition responsive characteristics of poly(N-isopropylacrylamide-co-benzo-12-crown-4-acrylamide) copolymers with benzo-12-crown-4 as both guest and host units.

Novel dual molecular- and ion-recognition responsive poly(N-isopropylacrylamide-co-benzo-12-crown-4-acrylamide) (PNB12 C4 ) linear copolymers with benzo-12-crown-4 (B12C4) as both guest and host units are prepared. The copolymers exhibit highly selective sensitivities toward γ-cyclodextrin (γ-CD) and Na(+) . The presence of γ-CD induces the lower critical solution temperature (LCST) of PNB12 C4 copolymer to shift to a higher value due to the formation of 1:1 γ-CD/B12C4 host-guest inclusion complexes, while Na(+) causes a negative shift in LCST due to the formation of 2:1 "sandwich" B12C4/Na(+) host-guest complexes. Regardless of the complexation order, when γ-CD and Na(+) coexist with PNB12 C4 , competitive complexation actions of B12C4 as both guest and host units toward γ-CD and Na(+) finally form equilibrium 2:2:1 γ-CD/B12C4/Na(+) composite complexes, and the final LCST values of PNB12 C4 copolymer reach almost the same level. The results provide valuable guidance for designing and applying PNB12 C4 -based smart materials in various applications.

A thermo-responsive hydrogel for body temperature-induced spontaneous information decryption and self-encryption.

A thermo-responsive poly(N-isopropylacrylamide) (PNIPAM) hydrogel, exhibiting an interesting phenomenon of an opaque-transparent-opaque transition in the successive processes of heating and cooling, is reported. It is fabricated by means of both the porogenic effect of hydroxypropyl cellulose and the cononsolvency effect of PNIPAM in a mixed solvent of dimethyl sulfoxide and water. After being mildly triggered by body temperature, the hydrogel is used to spontaneously decrypt the quick response code within 4 min and then autonomously encrypts the code again within 10 min at room temperature. The mechanism for the transient transparency of hydrogels during the quenching process has been elucidated.

Dialdehyde starch cross-linked aminated gelatin sponges with excellent hemostatic performance and biocompatibility.

Developing a hemostatic material suitable for rapid hemostasis remains a challenge. This study presents a novel aminated gelatin sponge cross-linked with dialdehyde starch, exhibiting excellent biocompatibility and hemostatic ability. This aminated gelatin sponge features hydrophilic surface and rich porous structure with a porosity of up to 80 %. The results show that the aminated gelatin sponges exhibit superior liquid absorption capacity and can absorb up to 30-50 times their own mass of simulated body fluid within 5 min. Compared with the commercial gelatin hemostatic sponge and non-aminated gelatin hemostatic sponge, the aminated gelatin hemostatic sponge can accelerate the hemostatic process through electrostatic interactions, demonstrating superior hemostatic performance in both in vitro and in vivo hemostasis tests. The aminated gelatin sponge can effectively control the hemostatic time within 80 s in the in vivo rat femoral artery injury model, significantly outperforming both commercial and non-aminated gelatin sponges. In addition, the aminated gelatin sponge also exhibits good biocompatibility and certain antibacterial properties. The proposed aminated gelatin sponge has very good application prospects for the management of massive hemorrhage.

Dissolving microneedle system containing Ag nanoparticle-decorated silk fibroin microspheres and antibiotics for synergistic therapy of bacterial biofilm infection.

Most cases of delayed wound healing are associated with bacterial biofilm infections due to high antibiotic resistance. To improve patient compliance and recovery rates, it is critical to develop minimally invasive and efficient methods to eliminate bacterial biofilms as an alternative to clinical debridement techniques. Herein, we develop a dissolving microneedle system containing Ag nanoparticles (AgNPs)-decorated silk fibroin microspheres (SFM-AgNPs) and antibiotics for synergistic treatment of bacterial biofilm infection. Silk fibroin microspheres (SFM) are controllably prepared in an incompatible system formed by a mixture of protein and carbohydrate solutions by using a mild all-aqueous phase method and serve as biological templates for the synthesis of AgNPs. The SFM-AgNPs exert dose- and time-dependent broad-spectrum antibacterial effects by inducing bacterial adhesion. The combination of SFM-AgNPs with antibiotics breaks the limitation of the antibacterial spectrum and achieves better efficacy with reduced antibiotic dosage. Using hyaluronic acid (HA) as the soluble matrix, the microneedle system containing SFM-AgNPs and anti-Gram-positive coccus drug (Mupirocin) inserts into the bacterial biofilms with sufficient strength, thereby effectively delivering the antibacterial agents and realizing good antibiofilm effect on Staphylococcus aureus-infected wounds. This work demonstrates the great potential for the development of novel therapeutic systems for eradicating bacterial biofilm infections.