Water-in-Water Pickering Emulsion Stabilized by Polydopamine Particles and Cross-Linking

Interfacial Membranization of Regenerated Cellulose Nanoparticles and a Protein Renders Stable Water-in-Water Emulsion

Pickering water-in-water (W/W) emulsions stabilized by biobased colloids are pertinent to engineering biomaterials with hierarchical and confined architectures. In this study, stable W/W emulsions are developed through membranization utilizing biopolymer structures formed by the adsorption of cellulose II nanospheres and a globular protein, bovine serum albumin (BSA), at droplet surfaces. The produced cellulose II nanospheres (NPcat, 63 nm diameter) bearing a soft and highly accessible shell, endow rapid and significant binding (16 mg cm- 2) with BSA. NPcat and BSA formed complexes that spontaneously stabilized liquid droplets, resulting in stable W/W emulsions. It is proposed that such a system is a versatile all-aqueous platform for encapsulation, (bio)catalysis, delivery, and synthetic cell mimetics.

High precision acoustofluidic synthesis of stable, biocompatible water-in-water emulsions

Water-in-water (w/w) emulsions, comprising aqueous droplets within another continuous aqueous phase, rely on a low interfacial tension for stability. Thus far, it has been challenging to control their size and stability without the use of stabilizers. In this study, we introduce a microfluidic technique that addresses these challenges, producing stable w/w emulsions with precisely controlled size and uniformity. Results shows that using an acoustically actuated microfluidic mixer, PEG, Dextran, and alginate solutions (84.66 mPa.s viscosity difference) were homogenized rapidly, forming uniformly distributed w/w emulsions stabilized in alginate gels. The emulsion size, uniformity, and shear sensitivity can be tuned by modifying the alginate concentration. Biocompatibility was evaluated by monitoring the viability of kidney cells in the presence of emulsions and gels. In conclusion, this study not only showed emulsion formation with a high mixing efficiency exceeding 90 % for all viscosities, actuated at an optimized frequency of 1.064 MHz, but also demonstrated that an aqueous, solvent, and emulsifier-free composition exhibited remarkable biocompatibility, holding promise for precise drug delivery, cosmetics, and food applications.

DNA-Origami-Armored DNA Condensates

DNA condensates, formed by liquid-liquid phase separation (LLPS), emerge as promising soft matter assemblies for creating artificial cells. The advantages of DNA condensates are their molecular permeability through the surface due to their membrane-less structure and their fluidic property. However, they face challenges in the design of their surface, e. g., unintended fusion and less regulation of permeable molecules. Addressing them, we report surface modification of DNA condensates with DNA origami nanoparticles, employing a Pickering-emulsion strategy. We successfully constructed core-shell structures with DNA origami coatings on DNA condensates and further enhanced the condensate stability toward fusion via connecting DNA origamis by responding to DNA input strands. The 'armoring' prevented the fusion of DNA condensates, enabling the formation of multicellular-like structures of DNA condensates. Moreover, the permeability was altered through the state change from coating to armoring the DNA condensates. The armored DNA condensates have significant potential for constructing artificial cells, offering increased surface stability and selective permeability for small molecules while maintaining compartmentalized space and multicellular organization.

Water-in-water emulsions stabilized by nano-chitin

A water-in-water (W/W) emulsion consists of microdroplets was formed by the spontaneous liquid-liquid separation by mixing polyacrylic acid and chitosan oligosaccharide in water, and these microdropletes were stabilized by nano-chitin, formed water-in-water Pickering emulsions. By taking the advantage of interfacial adsorption of nano-chitin, the W/W emulsion droplets composed of polyacrylic acid/chitosan oligosaccharide (COS/PAA) polyelectrolyte coacervate were successfully stabilized. Research results indicated that composite microspheres were formed by the nano-chitin stabilized COS/PAA emulsion, and the size of these composite microspheres was related to the concentration and morphology of the nano-chitin. As the concentration of nano-chitin increases, the size of the composite microspheres first increases and then decreases, gradually becoming more uniform; whereas a decrease in the length of nano-chitin will lead to an increase in the size of the composite microspheres. The formation of composite microspheres may be due to the electrostatic interactions between nano-chitin and the emulsion droplets. In addition, the composite microspheres exhibit the best release effect for berberine hydrochloride at a pH value of 3.

Exploring the potential of all-aqueous immiscible systems for preparing complex biomaterials and cellular constructs

All-aqueous immiscible systems derived from liquid-liquid phase separation of incompatible hydrophilic agents such as polymers and salts have found increasing interest in the biomedical and tissue engineering fields in the last few years. The unique characteristics of aqueous interfaces, namely their low interfacial tension and elevated permeability, as well as the non-toxic environment and high water content of the immiscible phases, confer to these systems optimal qualities for the development of biomaterials such as hydrogels and soft membranes, as well as for the preparation of in vitro tissues derived from cellular assembly. Here, we overview the main properties of these systems and present a critical review of recent strategies that have been used for the development of biomaterials with increased levels of complexity using all-aqueous immiscible phases and interfaces, and their potential as cell-confining environments for micropatterning approaches and the bioengineering of cell-rich structures. Importantly, due to the relatively recent emergence of these areas, several key design considerations are presented, in order to guide researchers in the field. Finally, the main present challenges, future directions, and adaptability to develop advanced materials with increased biomimicry and new potential applications are briefly evaluated.

Thermally-resilient, phase-invertible, ultra-stable all-aqueous compartments by pH-modulated protein colloidal particles

The essence of compartmentalization in cells is the inspiration behind the engineering of synthetic counterparts, which has emerged as a significant engineering theme. Here, we report the formation of ultra-stable water-in-water (W/W) emulsion droplets. These W/W droplets demonstrate previously unattained stability across a broad pH spectrum and exhibit resilience at temperatures up to 80℃, overcoming the challenge of insufficient robustness in dispersed droplets of aqueous two-phase systems (ATPS). The exceptional robustness is attributed to the strong anchoring of micelle-like casein colloidal particles at the PEO/DEX interface, which maintains stability under varying environmental conditions. The increased surface hydrophobicity of these particles at high temperatures contributes to the formation of thermally-stable droplets, enduring temperatures as high as 80℃. Furthermore, our study illustrates the adaptable affinity of micelle-like casein colloidal particles towards the PEO/DEX-rich phase, enabling the formation of stable DEX-in-PEO emulsions at lower pH levels, and PEO-in-DEX emulsions as the pH rises above the isoelectric point. The robust nature of these W/W emulsions unlocks new possibilities for exploring various biochemical reactions within synthetic subcellular modules and lays a solid foundation for the development of novel biomimetic materials.

Revolutionizing targeting precision: microfluidics-enabled smart microcapsules for tailored delivery and controlled release

As promising delivery systems, smart microcapsules have garnered significant attention owing to their targeted delivery loaded with diverse active materials. By precisely manipulating fluids on the micrometer scale, microfluidic has emerged as a powerful tool for tailoring delivery systems based on potential applications. The desirable characteristics of smart microcapsules are associated with encapsulation capacity, targeted delivery capability, and controlled release of encapsulants. In this review, we briefly describe the principles of droplet-based microfluidics for smart microcapsules. Subsequently, we summarize smart microcapsules as delivery systems for efficient encapsulation and focus on target delivery patterns, including passive targets, active targets, and microfluidics-assisted targets. Additionally, based on release mechanisms, we review controlled release modes adjusted by smart membranes and on/off gates. Finally, we discuss existing challenges and potential implications associated with smart microcapsules.

Melanin-Inspired Composite Materials: From Nanoarchitectonics to Applications

Synthetic melanin is a mimic of natural melanin analogue with intriguing properties such as metal-ion chelation, redox activity, adhesion, and broadband absorption. Melanin-inspired composite materials are formulated by assembly of melanin with other types of inorganic and organic components to target, combine, and build up the functionality, far beyond their natural capabilities. Developing efficient and universal methodologies to prepare melanin-based composite materials with unique functionality is vital for their further applications. In this review, we summarize three types of synthetic approaches, predoping, surface engineering, and physical blending, to access various melanin-inspired composite materials with distinctive structure and properties. The applications of melanin-inspired composite materials in free radical scavenging, bioimaging, antifouling, and catalytic applications are also reviewed. This review also concludes current challenges that must be addressed and research opportunities in future studies.

Tuning the bis-hydrophilic balance of microgels: A tool to control the stability of water-in-water emulsions

HYPOTHESIS

The stability of purely aqueous emulsions (W/W) formed by mixing incompatible polymers, can be achieved through the Pickering effect of particles adsorption at the interface. However, there is, as yet, no guideline regarding the chemical nature of the particles to predict whether they will stabilize a particular W/W emulsion. Bis-hydrophilic soft microgels, made of copolymerized poly(N-isopropylacrylamide) (pNIPAM) and dextran (Dex), act as very efficient stabilizers for PEO/Dextran emulsions, because the two polymers have an affinity for each polymer phase.

EXPERIMENTS

The ratio between both components of the microgels is varied in order to modulate the bis-hydrophilic balance, the content of Dex compared to pNIPAM varying from 0 to 60 wt%. The partition between the two aqueous phases and the adsorption of microgels at the W/W interface is measured by confocal microscopy. The stability of emulsions is assessed via turbidity measurements and microstructural investigations under sedimentation or compression.

FINDINGS

The adsorption of particles and their partitioning is found to evolve progressively as a function of bis-hydrophilic balance. At room temperature, the stability of the resulting W/W emulsions also depends on the bis-hydrophilic balance with a maximum of stability for the particles containing 50%wt of Dex, for the Dex-in-PEO emulsions, while the PEO-in-Dex become stable above this value. The thermo-responsiveness of the microgels translates into stability inversion of the emulsions below 50 wt% of Dex in the microgels, whereas above 50 wt%, no emulsion is stable. This work paves the way of a guideline to design efficient and responsive W/W stabilizers.

Effect of adding gelatin on the stability of water in water emulsions formed by mixtures of amylopectin and guar gum

Stable water in water (W/W) emulsions of guar rich droplets dispersed in an amylopectin rich continuous phase (G/A) and the inverse (A/G) can be achieved by adding gelatin and inducing microphase separation of the latter by cooling. In this research, the effect of gelatin on the emulsion stability was further studied by storing the emulsions at 10, 20 and 25 °C. The visual aspect, the microstructure, and the viscosity of the emulsions were investigated at different times during storage at different temperatures and pH. It was found that depending on the conditions, the gelatin phase wetted the interface or formed small discrete microdomains that adsorbed at the interface and dispersed in the bulk phases. The observed differences in morphology and stability are related to the interplay of the rates of aggregation, phase separation of gelatin, which itself depend on the gelatin concentration, temperature and pH. Emulsions could be prepared in this manner that were stable for at least one week and remained visually homogeneous. We believe that this is a promising method to stabilize W/W emulsions as long as the components of the emulsion are incompatible with aggregated gelatin.

Effect of charge on the stabilization of water-in-water emulsions by thermosensitive bis-hydrophilic microgels

HYPOTHESIS

Molecular surfactants are not able to stabilize water-in-water (W/W) emulsions, unlike nano or micro-particles, which can achieve this in some cases. However, the effect of electrostatic interactions between particles on the emulsion stability has rarely been investigated. We hypothesize that introducing charges modifies the stabilization capacity of particles and renders it both pH- and ionic strength-dependent.

EXPERIMENTS

Charge was introduced into bis-hydrophilic and thermoresponsive dextran/polyN-isopropylacrylamide microgels by replacing a small fraction of polyN-isopropylacrylamide with acrylic acid groups. The size of the microgels was obtained by dynamic light scattering. The stability and microstructure of dextran/poly(ethyleneoxide)-based W/W emulsions, was studied as a function of pH, NaCl concentration and temperature using confocal microscopy and by analytical centrifugation.

FINDINGS

The swelling degree of charged microgels depends on the pH, ionic strength and the temperature. In the absence of salt, charged microgels do not adsorb at the interface and have little stabilizing effect even after neutralization. However, the interfacial coverage and the stability increase with rising concentration of NaCl. Saltinduced stabilization of these emulsions was also observed at 50 °C. Increasing the temperature strongly influences the emulsion stability at low pH.

Preparation and characterization of ultrasound-assisted essential oil-loaded nanoemulsions stimulated pullulan-based bioactive film for strawberry fruit preservation

Ultrasound is a high-energy approach that can help with homogenization and dispersion in cavitation. In this study, nanoemulsions of curcumin and orange essential oil were prepared with ultrasound treatment at different times. The ultrasound-treated nanoemulsions for 10 min exhibited the smallest droplet size, the best storage, and higher thermal stability. The pullulan-based film with ultrasound-assisted nanoemulsions exhibited improved water vapor permeability and moisture content and the highest tensile strength and elongation at break. The structural analysis showed that ultrasonic treatment enhanced the H-bond, resulting in a more orderly molecular arrangement and intermolecular compatibility. Furthermore, the bioactive film had the maximum oil retention time. It possessed excellent bacteriostatic properties against Escherichia coli and Staphylococcus aureus due to the smallest oil droplets and uniform distribution in the film matrix. Besides, the weight loss and deterioration of the strawberry fruit were effectively reduced, thus prolonging the shelf life.

Water-in-Water Emulsions Stabilized by Silica Janus Nanosheets

Water-in-water (w/w) emulsions have been recognized for their broad applications in foods, cosmetics, and biomedical engineering. In this work, silica Janus nanosheets (JNs) with polyacrylic acid (PAA) chains grafted on one surface via crushing functional silica foams, and used silica JNs as Pickering stabilizer to produce stable water-in-water (w/w) emulsions from the aqueous two-phase system (ATPS) containing methacrylic acid (MAA) and NaCl are prepared. The interfacial area of w/w emulsions increases linearly with the concentration of silica JNs, and the interfacial coverage of nanosheets is calculated to be about 98%. After polymerizing w/w emulsions prepared from MAA/NaCl ATPS, it is found that silica JNs are entrapped at the interface of w/w emulsions with the smooth PAA-grafted surface located toward MAA-rich phase due to their specific interaction. These results show that functional silica JNs can be used as a promising amphiphilic Pickering stabilizer to produce well-defined w/w emulsions for numerous application fields.

Unconventional and conventional Pickering emulsions: Perspectives and challenges in skin applications

Pickering emulsions are free from molecular and classical surfactants and are stabilized by solid particles, creating long-term stability against emulsion coalescence. Additionally, these emulsions are both environmentally and skin-friendly, creating new and unexplored sensorial perceptions. Although the literature mostly describes conventional emulsions (oil-in-water), there are unconventional emulsions (multiple, oil-in-oil and water-in-water) with excellent prospects and challenges in skin application as oil-free systems, permeation enhancers and topical drug delivery agents, with various possibilities in pharmaceutical and cosmetic products. However, up to now, these conventional and unconventional Pickering emulsions are not yet available as commercial products. This review brings to the discussion some important aspects such as the use of phases, particles, rheological and sensorial perception, as well as current trends in the development of these emulsions.

Water-in-water emulsions stabilized by self-assembled chitosan colloidal particles

Dextran (Dex) and poly(ethylene glycol) (PEG)-based aqueous emulsions were stabilized using the self-assembled chitosan colloidal particles (CS CPs). Besides, the effects of pH, CS CPs concentration, polymer concentration, volume ratio of PEG solution to Dex solution, temperature, homogenizing speed and homogenizing time on the property of the W/W emulsions were investigated, respectively. In order to enhance the stability of the PEG-Dex emulsion, sodium tripolyphosphate was used to cross-link the CS CPs at the interface of emulsion droplets, which resulted in the stability duration for >1 year. Finally, the CS CPs were used as a support to immobilize urease and bovine serum albumin and a stabilizer to prepare W/W emulsion, which were then adopted as a catalysis system and as a spinning solution to fabricate drug-loaded nanofiber. This strategy potentially provides a new opportunity to encapsulate the active molecules at the water-water interface, and enrich the types of usable active molecules in the encapsulation in the W/W emulsions.

Recent advances in bioactive nanocrystal-stabilized Pickering emulsions: Fabrication, characterization, and biological assessment

Numerous literatures have shown the advantages of Pickering emulsion (PE) for the delivery of bioactive ingredients in the fields of food, medicine, and cosmetics, among others. On this basis, the multi-loading mode of bioactives (internal phase encapsulation and/or loading at the interface) in small molecular bioactives nanocrystal-stabilized PE (BNC-PE) enables them higher loading efficiencies, controlled release, and synergistic or superimposed effects. Therefore, BNC-PE offers an efficacious delivery system. In this review, we briefly summarize BNC-PE fabrication and characterization, with a focus on the processes of possible evolution and absorption of differentially applied BNC-PE when interacting with the body. In addition, methods of monitoring changes and absorption of BNC-PE in vivo, from the nanomaterial perspective, are also introduced. The purpose of this review is to provide an accessible and comprehensive methodology for the characterization and evaluation of BNC-PE after formulation and preparation, especially in relation to biological assessment and detailed mechanisms throughout the absorption process of BNC-PE in vivo.

Bacteria-Inspired Aqueous-in-Aqueous Compartmentalization by In Situ Interfacial Biomineralization

Compartmentalization is essential for living cells to orchestrate their biological processes with controlled external influences. Thus, compartmentalization has been a constant theme for cell-mimicking materials. Despite recent advances in engineering compartmentalized materials as synthetic cells and organelles, it remains difficult to produce robust and well-ordered compartments with secluded environments in aqueous surroundings. Nature creates hierarchically ordered compartmentalized materials by utilizing bio-catalyzed mineralization, inspired by which, mechanically robust all-aqueous compartments are developed by engineering a mild biomimetic mineralization at aqueous/aqueous interfaces. The enzyme-induced biomineralization generates a layer of densely-packed particles, acting as an armor to enclose aqueous interiors. This strategy of in situ bio-synthesized compartments is different from current strategies, where compartments are constructed by randomly adsorbed particles at interface, leading to inadequately controlled properties of compartments. To demonstrate the robustness and adaptiveness of the in situ bio-synthesized all-aqueous compartments, these are utilized as drug delivery materials by sequestering protein drugs at their aqueous interiors and releasing when exposing to gastric environments. The study provides new ways to fabricate compartmentalized materials with well-defined properties, unlocking routes to the next generation of self-assembled materials and structures by integrating aqueous two-phase systems with biomineralization.

Recent progress in the synthesis of all-aqueous two-phase droplets using microfluidic approaches

An aqueous two-phase system (ATPS) is a system with liquid-liquid phase separation and shows great potential for the extraction, separation, purification, and enrichment of proteins, membranes, viruses, enzymes, nucleic acids, and other biomolecules because of its simplicity, biocompatibility, and wide applicability [1-4]. The clear aqueous-aqueous interface of ATPSs is highly advantageous for their implementation, therefore making ATPSs a green alternative approach to replace conventional emulsion systems, such as water-in-oil droplets. All aqueous emulsions (water-in-water, w-in-w) hold great promise in the biomedical field as glucose sensors [5] and promising carriers for the encapsulation and release of various biomolecules and nonbiomolecules [6-10]. However, the ultralow interfacial tension between the two phases is a hurdle in generating w-in-w emulsion droplets. In the past, bulk emulsification and electrospray techniques were employed for the generation of w-in-w emulsion droplets and the fabrication of microparticles and microcapsules in the later stage. Bulk emulsification is a simple and low-cost technique; however, it generates polydisperse w-in-w emulsion droplets. Another technique, electrospray, involves easy experimental setups that can generate monodisperse but nonspherical w-in-w emulsion droplets. In comparison, microfluidic platforms provide monodisperse w-in-w emulsion droplets with spherical shapes, deal with the small volumes of solutions and short reaction times and achieve portability and versatility in their design through rapid prototyping. Owing to several advantages, microfluidic approaches have recently been introduced. To date, several different strategies have been explored to generate w-in-w emulsions and multiple w-in-w emulsions and to fabricate microparticles and microcapsules using conventional microfluidic devices. Although a few review articles on ATPSs emulsions have been published in the past, to date, few reviews have exclusively focused on the evolution of microfluidic-based ATPS droplets. The present review begins with a brief discussion of the history of ATPSs and their fundamentals, which is followed by an account chronicling the integration of microfluidic devices with ATPSs to generate w-in-w emulsion droplets. Furthermore, the stabilization strategies of w-in-w emulsion droplets and microfluidic fabrication of microparticles and microcapsules for modern applications, such as biomolecule encapsulation and spheroid construction, are discussed in detail in this review. We believe that the present review will provide useful information to not only new entrants in the microfluidic community wanting to appreciate the findings of the field but also existing researchers wanting to keep themselves updated on progress in the field.

Microfluidic preparation of a novel phoxim nanoemulsion pesticide against Spodoptera litura

With continuous development of pesticide dosage forms, emulsifiable concentrates using large amounts of organic solvents are gradually obsoleted. Nanoemulsions with high water content have been developed and the preparation processes also evolved, but these processes still exist some problems, such as poor controllability and high energy consumption. Microfluidic is a controllable nanoemulsion preparation system which mainly applied to pharmaceutical synthesis. In this study, the pesticide phoxim nanoemulsion was prepared by microfluidic technology. The optimized formulation of phoxim nanoemulsion was composed of Tween 80 and pesticide emulsifier 500 as surfactant, hexyl acetate as oil, and n-propanol as co-surfactant. Moreover, when the flow rates of water and oil in the microfluidic system were adjusted to 5 μL/min and 20 μL/min, phoxim nanoemulsion was obtained with a cloud point/boiling point of 109 °C, a particle size of 21.5 ± 0.8 nm and a potential value of - 18.7 ± 0.6 mV. Furthermore, the nanoemulsion had a rapid release effect in vitro which could be fitted by the Ritger-Peppas model. The feeding toxicity of the phoxim nanoemulsion was higher than that of commercial formulation while the contact killing effect was higher than that of the active ingredient. Therefore, pesticide dosage was reduced and the insecticidal effect was enhanced by using phoxim nanoemulsions. These results also confirm the potential of microfluidics as a green process to produce pesticide nanoemulsions.

Progress in all-aqueous droplets generation with microfluidics: Mechanisms of formation and stability improvements

All-aqueous systems have attracted intensive attention as a promising platform for applications in cell separation, protein partitioning, and DNA extraction, due to their selective separation capability, rapid mass transfer, and good biocompatibility. Reliable generation of all-aqueous droplets with accurate control over their size and size distribution is vital to meet the increasingly growing demands in emulsion-based applications. However, the ultra-low interfacial tension and large effective interfacial thickness of the water-water interface pose challenges for the generation and stabilization of uniform all-aqueous droplets, respectively. Microfluidics technology has emerged as a versatile platform for the precision generation of all-aqueous droplets with improved stability. This review aims to systematize the controllable generation of all-aqueous droplets and summarize various strategies to improve their stability with microfluidics. We first provide a comprehensive review on the recent progress of all-aqueous droplets generation with microfluidics by detailing the properties of all-aqueous systems, mechanisms of droplet formation, active and passive methods for droplet generation, and the property of droplets. We then review the various strategies used to improve the stability of all-aqueous droplets and discuss the fabrication of biomaterials using all-aqueous droplets as liquid templates. We envision that this review will benefit the future development of all-aqueous droplet generation and its applications in developing biomaterials, which will be useful for researchers working in the field of all-aqueous systems and those who are new and interested in the field.

Vascularized Co-Culture Clusteroids of Primary Endothelial and Hep-G2 Cells Based on Aqueous Two-Phase Pickering Emulsions

Three-dimensional cell culture has been extensively involved in biomedical applications due to its high availability and relatively mature biochemical properties. However, single 3D cell culture models based on hydrogel or various scaffolds do not meet the more in-depth requirements of in vitro models. The necrotic core formation inhibits the utilization of the 3D cell culture ex vivo as oxygen permeation is impaired in the absence of blood vessels. We report a simple method to facilitate the formation of angiogenic HUVEC (human umbilical vein endothelial cells) and Hep-G2 (hepatocyte carcinoma model) co-culture 3D clusteroids in a water-in-water (w/w) Pickering emulsions template which can overcome this limitation. This method enabled us to manipulate the cells proportion in order to achieve the optimal condition for stimulating the production of various angiogenic protein markers in the co-cultured clusteroids. The HUVEC cells respond to the presence of Hep-G2 cells and their byproducts by forming endothelial cell sprouts in Matrigel without the exogenous addition of vascular endothelial growth factor (VEGF) or other angiogenesis inducers. This culture method can be easily replicated to produce other types of cell co-culture spheroids. The w/w Pickering emulsion template can facilitate the fabrication of 3D co-culture models to a great extent and be further utilized in drug testing and tissue engineering applications.

Thermo-induced inversion of water-in-water emulsion stability by bis-hydrophilic microgels

HYPOTHESIS

Stabilization of water-in-water (W/W) emulsions resulting from the separation of polymeric phases such as dextran (DEX) and poly(ethyleneoxide) (PEO) is highly challenging, because of the very low interfacial tensions between the two phases and because of the interface thickness extending over several nanometers. In the present work, we present a new type of stabilizers, based on bis-hydrophilic, thermoresponsive microgels, incorporating in the same structure poly(N-isopropylacrylamide) (pNIPAM) chains having an affinity for the PEO phase and dextran moieties. We hypothesize that these particles allow better control of the stability of the W/W emulsions.

EXPERIMENTS

The microgels were synthesized by copolymerizing the NIPAM monomer with a multifunctional methacrylated dextran. They were characterized by dynamic light scattering, zeta potential measurements and nuclear magnetic resonance as a function of temperature. Microgels with different compositions were tested as stabilizers of droplets of the PEO phase dispersed in the DEX phase (P/D) or vice-versa (D/P), at different concentrations and temperatures.

FINDINGS

Only microgels with the highest DEX content revealed excellent stabilizing properties for the emulsions by adsorbing at the droplet surface, thus demonstrating the fundamental role of bis-hydrophilicity. At room temperature, both pNIPAM and DEX chains were swollen by water and stabilized better D/P emulsions. However, above the volume phase transition temperature (VPTT ≈ 32 °C) of pNIPAM the microgels shrunk and stabilized better P/D emulsions. At all temperatures, excess microgels partitioned more to the PEO phase. The change in structure and interparticle interaction induced by heating can be exploited to control the W/W emulsion stability.

Multicompartment Hydrogels

Hydrogels belong to the most promising materials in polymer and materials science at the moment. As they feature soft and tissue-like character as well as high water-content, a broad range of applications are addressed with hydrogels, e.g. tissue engineering and wound dressings but also soft robotics, drug delivery, actuators and catalysis. Ways to tailor hydrogel properties are crosslinking mechanism, hydrogel shape and reinforcement, but new features can be introduced by variation of hydrogel composition as well, e.g. via monomer choice, functionalization or compartmentalization. Especially, multicompartment hydrogels drive progress towards complex and highly functional soft materials. In the present review the latest developments in multicompartment hydrogels are highlighted with a focus on three types of compartments, i.e. micellar/vesicular, droplets or multi-layers including various sub-categories. Furthermore, several morphologies of compartmentalized hydrogels and applications of multicompartment hydrogels will be discussed as well. Finally, an outlook towards future developments of the field will be given. The further development of multicompartment hydrogels is highly relevant for a broad range of applications and will have a significant impact on biomedicine and organic devices. This article is protected by copyright. All rights reserved.

pH sensitive water-in-water emulsions based on the pullulan and poly(N,N-dimethylacrylamide) aqueous two-phase system

A novel aqueous two-phase system based on pullulan and poly(N,N-dimethylacrylamide) is presented. Furthermore, it is used for the formation of pH sensitive water-in-water emulsions.

Selective identification and separation of ReO4- by biomimetic flexible temperature-sensitive imprinted composite membranes

A new type of temperature-sensitive imprinted composite membranes(ICMs) was developed. Poly N,N-diethylacrylamide (DEA) blocks, as temperature-sensitive polymer, were grafted onto the substrate of the imprinted polymer separation layer to endow membranes with better adsorption effect. The comprehensive properties of the imprinted composite membranes were adequately tested and evaluated in detail. Results showed that ReO₄^- -ICMs (Re-ICMs) with temperature-sensitive recognition sites could adjust the structure of the imprinted holes at different temperatures, which presented excellent performance in the selective separation and purification of ReO₄^-. The prepared Re-ICMs exhibit the maximum adsorption capacity of 0.1639 mmol/g at 35 °C with the equilibrium adsorption time of 2 h. After ten adsorption/desorption cycles, Re-ICMs could still maintain 73.5% of the original adsorption capacity, the separation degree of ReO₄^-/MnO₄^- was only reduced from the initial 24.5 to 15.9, and the desorption ratio dropped from 80.4% to 68.4%, indicating that Re-ICMs have excellent adsorption and separation performance and reusability.

Novel analytical expressions for determining van der Waals interaction between a particle and air-water interface: Unexpected stronger van der Waals force than capillary force

HYPOTHESIS

Analytical expressions for calculating Hamaker constant (HC) and van der Waals (VDW) energy/force for interaction of a particle with a solid water interface has been reported for over eighty years. This work further developed novel analytical expressions and numerical approaches for determining HC and VDW interaction energy/force for the particle approaching and penetrating air-water interface (AWI), respectively.

METHODS

The expressions of HC and VDW interaction energy/force before penetrating were developed through analysis of the variation in free energy of the interaction system with bringing the particle from infinity to the vicinity of the AWI. The surface element integration (SEI) technique was modified to calculate VDW energy/force after penetrating.

FINDINGS

We explain why repulsive VDW energy exists inhibiting the particle from approaching the AWI. We found very significant VDW repulsion for a particle at a concave AWI after penetration, which can even exceed the capillary force and cause strong retention in water films on a solid surface and at air-water-solid interface line. The methods and findings of this work are critical to quantification and understanding of a variety of engineered processes such as particle manipulation (e.g., bubble flotation, Pickering emulsion, and particle laden interfaces).

Water-in-water Pickering emulsions stabilized by the starch nanocrystals with various surface modifications

HYPOTHESIS

Using the platelet-like starch nanocrystals (SNCs) to stabilize emulsions is attractive because as-prepared emulsions have promising applications in cosmetics and food fields. Limited studies mainly focus on the oil-in-water system, and another important system, the water-in-water emulsions stabilized by SNCs, has not yet been unveiled.

EXPERIMENTS

Two surface modification strategies, crosslinking and acetylation, were applied to tune surface property and aggregation of SNCs, and a common all-aqueous system (dextran/poly(ethylene glycol)) was used here as template. The viscoelasticity and morphology of emulsions were studied in terms of the SNC loadings and polymer ratios.

FINDINGS

Crosslinking results in aggregation of SNCs, and the particle size increases (from 110 nm to 370 nm) with increased levels of substitution. This favors improving emulsifying ability of particles. Acetylation decreases the particle size (∼90 nm) and weakens the affinity of SNCs to the two aqueous phases, improving the emulsifying efficiency of SNCs. More intriguingly, the two emulsion systems show different phase inversion behaviors. The depletion-stabilization mechanism for the cross-linked SNCs and the diffusion-controlled mechanism for the acetylated SNCs are proposed using the emulsion viscoelasticity as probe. This study makes a comprehensive insight into the regulation of water-in-water emulsion morphology and types with the platelet-like SNCs.

The Art of Framework Construction: Core-Shell Structured Micro-Energetic Materials

Weak interfacial interactions remain a bottleneck for composite materials due to their weakened performance and restricted applications. The development of core–shell engineering shed light on the preparation of compact and intact composites with improved interfacial interactions. This review addresses how core–shell engineering has been applied to energetic materials, with emphasis upon how micro-energetic materials, the most widely used particles in the military field, can be generated in a rational way. The preparation methods of core–shell structured explosives (CSEs) developed in the past few decades are summarized herein. Case studies on polymer-, explosive- and novel materials-based CSEs are presented in terms of their compositions and physical properties (e.g., thermal stability, mechanical properties and sensitivity). The mechanisms behind the dramatic and divergent properties of CSEs are also clarified. A glimpse of the future in this area is given to show the potential for CSEs and some suggestions regarding the future research directions are proposed.

Preparation and characterization of clove essential oil loaded nanoemulsion and pickering emulsion activated pullulan-gelatin based edible film

The clove essential oil (CEO) loaded nano and pickering emulsions prepared with Tween 80 and whey protein isolate/inulin mixture, respectively were incorporated into pullulan-gelatin film base fluid at three levels (0.2%, 0.4%, and 0.6%). The droplet sizes of NE and PE loaded with CEO were 15.93 nm and 266.9 nm, respectively. The PDI of CEOs with stable NE and PE were 0.262 and 0.259, respectively. Our results showed the improved compatibility between pullulan-gelatin and essential oil-loaded nanocarriers. The active film composed of PE carrier had the structural characteristics of high density, low water content, and low permeability, thus exhibiting excellent mechanical properties, water barrier properties, and appreciable antioxidant activities. Compared with NE, it was found that the CEO-loaded PE showed slow-release profile in the film sample. The prepared active film containing PE possessed a great potential to be used as effective and natural alternatives for active food packaging.

Polysaccharide nanoparticles: from fabrication to applications

The present review highlights the developments in polysaccharide nanoparticles with a particular focus on applications in biomedicine, cosmetics and food.

Self-Emergent Protocells Generated in an Aqueous Solution with Binary Macromolecules through Liquid-Liquid Phase Separation

Recently, liquid-liquid phase separation (LLPS) has attracted considerable attention among researchers in the life sciences as a plausible mechanism for the generation of microstructures inside cells. LLPS occurs through multiple nonspecific interactions and does not always require a lock-and-key interaction with a binary macromolecular solution. The remarkable features of LLPS include the non-uniform localization and concentration of solutes, resulting in the ability to isolate certain chemical systems and thereby parallelize multiple chemical reactions within the limited space of a living cell. We report that, by using the macromolecules, poly(ethylene glycol) (PEG) and dextran, that exhibit LLPS in an aqueous solution, cell-sized liposomes are spontaneously formed therein in the presence of phospholipids. In this system, LLPS is generated through the depletion effect of macromolecules. The results showed that cell-like microdroplets entrapping DNA wrapped by a phospholipid layer emerge in a self-organized manner.

Graphitic Carbon Nitride Stabilized Water-in-Water Emulsions

Aqueous multiphase systems have attracted a lot of interest recently espeically due to target applications in the biomedical field, cosmetics, and food. In turn, water-in-water Pickering emulsions are investigated frequently. In here, graphitic carbon nitride (g-CN) stabilized water-in-water Pickering emulsions are fabricated via the dextran and poly(ethylene glycol)-based aqueous two-phase system. Five different derivatives of g-CN as the Pickering stabilizer are described and the effect of g-CN concentration on droplet sizes is investigated. Stable emulsions (up to 16 weeks) are obtained that can be broken on purpose via various approaches, including dilution, surfactant addition, and most notably light irradiation. The novel approach of water-in-water emulsion stabilization via g-CN opens up considerable advances in aqueous multiphase systems and may also introduce photocatalytic properties.

Advances and Opportunities of Oil-in-Oil Emulsions

Emulsions are mixtures of two immiscible liquids in which droplets of one are dispersed in a continuous phase of the other. The most common emulsions are oil-water systems, which have found widespread use across a number of industries, for example, in the cosmetic and food industries, and are also of advanced scientific interest. In addition, the past decade has seen a significant increase in both the design and application of nonaqueous emulsions. This has been primarily driven by developments in understanding the mechanism of effective stabilization of oil-in-oil (o/o) systems, either using block copolymers (BCPs) or solid (Pickering) particles with appropriate surface functionality. These systems, as highlighted in this review, have enabled emergent applications in areas such as pharmaceutical delivery, energy storage, and materials design (e.g., polymerization, monolith, and porous polymer synthesis). These o/o emulsions complement traditional emulsions that utilize an aqueous phase and allow the use of materials incompatible with water. We assess recent advances in the preparation and stabilization of o/o emulsions, focusing on the identity of the stabilizer (BCP or particle), the interplay between stabilizer and oils, and highlighting applications and opportunities associated with o/o emulsions.

Responsive Janus and Cerberus emulsions via temperature-induced phase separation in aqueous polymer mixtures

Complex aqueous emulsions represent a promising material platform for the encapsulation of cells, pharmaceuticals, or nutrients, for the fabrication of structured particles, as well as for mimicking the barrier-free compartmentalization of biomolecules found in living cells. Herein, we report a novel, simple, and scalable method of creating multicomponent aqueous droplets with highly uniform internal droplet morphologies that can be controllably altered after emulsification by making use of a thermal phase separation approach. Specifically, temperature-induced phase separation inside as-formed emulsion droplets comprising aqueous mixtures of two or more hydrophilic polymers allows for the generation of Janus and Cerberus emulsion droplets with adjustable internal morphologies that are solely controlled by a balance of interfacial tensions. We demonstrate our approach by applying both, microfluidic and scalable batch production, and present a detailed model study with predictive capabilities that enables fine-tuning and dynamically altering the droplet morphology as a function of types, molecular weights, and hydrophilicities of the polymers as well as the surfactant hydrophilic-lipophilic balance. The ability to rationally design complex aqueous emulsion droplets with previously unattainable dynamic control over their morphologies after emulsification entails the potential to design new responsive soft materials with implications for a variety of applications beyond encapsulation, including the design of complex adaptive and self-regulating materials, e.g. for chemical and biological sensing applications.

From Bioinspired Glue to Medicine: Polydopamine as a Biomedical Material

Biological structures have emerged through millennia of evolution, and nature has fine-tuned the material properties in order to optimise the structure-function relationship. Following this paradigm, polydopamine (PDA), which was found to be crucial for the adhesion of mussels to wet surfaces, was hence initially introduced as a coating substance to increase the chemical reactivity and surface adhesion properties. Structurally, polydopamine is very similar to melanin, which is a pigment of human skin responsible for the protection of underlying skin layers by efficiently absorbing light with potentially harmful wavelengths. Recent findings have shown the subsequent release of the energy (in the form of heat) upon light excitation, presenting it as an ideal candidate for photothermal applications. Thus, polydopamine can both be used to (i) coat nanoparticle surfaces and to (ii) form capsules and ultra-small (nano)particles/nanocomposites while retaining bulk characteristics (i.e., biocompatibility, stability under UV irradiation, heat conversion, and activity during photoacoustic imaging). Due to the aforementioned properties, polydopamine-based materials have since been tested in adhesive and in energy-related as well as in a range of medical applications such as for tumour ablation, imaging, and drug delivery. In this review, we focus upon how different forms of the material can be synthesised and the use of polydopamine in biological and biomedical applications.

Cascade Kinetics in an Enzyme-Loaded Aqueous Two-Phase System

Macromolecular crowding plays a critical role in the kinetics of enzymatic reactions. Dynamic compartmentalization of biological components in living cells due to liquid-liquid phase separation represents an important cell regulatory mechanism that can increase enzyme concentration locally and influence the diffusion of substrates. In the present study, we probed partitioning of two enzymes (horseradish-peroxidase and urate-oxidase) in a poly(ethylene glycol)-dextran aqueous two-phase system (ATPS) as a function of salt concentration and ion position in the Hofmeister series. Moreover, we investigated enzymatic cascade reactions and their kinetics within the ATPS, which revealed a strong influence of the ion hydration stemming from the background electrolyte on the partitioning coefficients of proteins following the Hofmeister series. As a result, we were able to realize cross-partitioning of two enzymes because of different protein net charges at a chosen pH. Our study reveals a strong dependency of the enzyme activity on the substrate type and crowding agent interaction on the final kinetics of enzymatic reactions in the ATPS and therefore provides substantial implications en route toward dynamic regulation of reactivity in synthetic protocells.

Emerging aqueous two-phase systems: from fundamentals of interfaces to biomedical applications

This review summarizes recent advances of aqueous two-phase systems (ATPSs), particularly their interfaces, with a focus on biomedical applications.

Temperature sensitive water-in-water emulsions

Temperature sensitive water-in-water (W/W) emulsions are described utilizing the thermal induced conformation change of tailored thermoresponsive block copolymers to reversibly stabilize and destabilize water–water interfaces.