Controllable Monodisperse Multiple Emulsions

Advancements in curcumin-loaded PLGA nanoparticle delivery systems: progressive strategies in cancer therapy

Cancer is a leading cause of death worldwide, and imposes a substantial socioeconomic burden with little impact especially on aggressive types of cancer. Conventional therapies have many serious side effects including generalised systemic toxicity which limits their long-term use. Tumour resistance and recurrence is another main problem associated with conventional therapy. Purified or extracted natural products have been investigated as cost-effective cancer chemoprotective agents with the potential to reverse or delaying carcinogenesis. Curcumin (CUR) as a natural polyphenolic component, exhibits many pharmacological activities such as anti-cancer, anti-inflammatory, anti-microbial, activity against neurodegenerative diseases including Alzheimer, antidiabetic activities (type II diabetes), anticoagulant properties, wound healing effects in both preclinical and clinical studies. Despite these effective protective properties, CUR has several limitations, including poor aqueous solubility, low bioavailability, chemical instability, rapid metabolism and a short half-life time. To overcome the pharmaceutical problems associated with free CUR, novel nanomedicine strategies (including polymeric nanoparticles (NPs) such as poly (lactic-co-glycolic acid) (PLGA) NPs have been developed. These formulations have the potential to improve the therapeutic efficacy of curcuminoids. In this review, we comprehensively summarise and discuss recent in vitro and in vivo studies to explore the pharmaceutical significance and clinical benefits of PLGA-NPs delivery system to improve the efficacy of CUR in the treatment of cancer.

Guest-guided anchoring patterns of cyclodextrin supramolecular microcrystals on droplet surfaces

The growth of cyclodextrin inclusion complexes (ICs) on oil/water interfaces represents a beautiful example of spontaneous pattern formation in nature. How the supramolecules evolve remains a challenge because surface confinement can frustrate microcrystal growth and give rise to unusual phase transitions. Here we investigate the self-assembly of ICs on droplet surfaces using microfluidics, which allows directly visualizing packing, wetting and ordering of the microcrystals anchored on the surface. The oil guests of distinct molecular structures can direct the assembly of the ICs and largely affect anchoring dynamics of the ICs microcrystals, leading to a range of behaviors including orientating, slipping, buckling, jamming, or merging. We discuss the behaviors observed in terms of the flexibility of the building blocks, which offers a new degree of freedom through which to tailor their properties and gives rise to a striking feature of anchoring patterns that have no counterpart in normal colloidal crystals.

Transparency-changing elastomers by controlling of the refractive index of liquid inclusions

Complex materials that change their optical properties in response to changes in environmental conditions can find applications in displays, smart windows, and optical sensors. Here a class of biphasic composites with stimuli-adaptive optical transmittance is introduced. The biphasic composites comprise aqueous droplets (a mixture of water, glycerol, and surfactant) embedded in an elastomeric matrix. The biphasic composites are tuned to be optically transparent through a careful match of the refractive indices between the aqueous droplets and the elastomeric matrix. We demonstrate that stimuli (e.g., salinity and temperature change) can trigger variations in the optical transmittance of the biphasic composite. The introduction of such transparency-changing soft matter with liquid inclusions offers a novel approach to designing advanced optical devices, optical sensors, and metamaterials.

Droplet drinking in constrictions

Droplets generated through microfluidics serve as a common platform for assembling artificial cells, which are feasibly tailored using microfluidic methodology. The ability of natural cells to undergo shape changes, such as phagocytosis, is a typical characteristic that researchers aim to mimic in artificial cells. However, simulating the deformation behavior of natural cells within droplets is exceptionally challenging. Here, this study reports a pinocytosis-like phenomenon observed in droplets, termed "droplet drinking". When droplets traverse a capillary with constrictions, the shear force from the continuous-phase fluid induces relative motion within the droplets, creating concave regions at the rear. These regions facilitate engulfing of the continuous-phase fluid, resulting in the formation of multiple emulsions. This behavior is influenced by the capillary number, and the size of the ingested droplets is governed by the interfacial tension between the two phases. The production of multicore or multi-shell emulsions can be easily accomplished by making slight adjustments to the constrictions. Furthermore, this method demonstrates the integration of reactants into pre-existing droplets, facilitating biochemical reactions. This study presents a convenient approach for generating complex emulsions and an innovative strategy for studying deformation behavior in droplet-based artificial cells.

Highly efficient and stable adsorption of lithium from brine with microcapsules containing 1-phenylazo-2-naphthol and trioctylphosphine oxide

Lithium extraction from salt lake brine is still challenging due to the existence of similar elements, e.g. sodium. In the present work, polysulfone (PSF) microcapsules containing 1-phenylazo-2-naphthol (HS) and trioctylphosphine oxide (TOPO) as extractants were successfully prepared by microfluidic technology for the separation of Li+ from brine with Li+ and Na+. The morphology, composition, and structure of HS-TOPO-based microcapsules were characterized systematically. The results showed that microcapsules consisting of 20 wt% (m m-1) polysulfone and 80 wt% (m m-1) 1-phenylazo-2-naphthol-trioctylphosphine oxide as the extractant, which was labeled as PSF/HS-TOPO-2/8, exhibited the best performance for Li+ adsorption. The separation factor (SF) of Li+ over Na+ is up to 653 and the adsorption capacity for Li+ in the simulated brine could reach 3.67 mg g-1 for microcapsules PSF/HS-TOPO-2/8, which demonstrated that Li+ can be separated with high selectivity. Besides, the kinetic results demonstrated that the adsorption followed quasi-secondary adsorption kinetic models, indicating that the adsorption mechanism of lithium by microcapsules involved chemisorption. After ten cycles of adsorption-elution, the maximum equilibrium adsorption capacity still remained at 87%. All these results demonstrate that PSF/HS-TOPO-2/8 microcapsules can be used as an efficient adsorber for the adsorption of Li+ from brine with high selectivity and stability.

Complex Emulsions as an Innovative Pharmaceutical Dosage form in Addressing the Issues of Multi-Drug Therapy and Polypharmacy Challenges

This review explores the intersection of microfluidic technology and complex emulsion development as a promising solution to the challenges of formulations in multi-drug therapy (MDT) and polypharmacy. The convergence of microfluidic technology and complex emulsion fabrication could herald a transformative era in multi-drug delivery systems, directly confronting the prevalent challenges of polypharmacy. Microfluidics, with its unparalleled precision in droplet formation, empowers the encapsulation of multiple drugs within singular emulsion particles. The ability to engineer emulsions with tailored properties-such as size, composition, and release kinetics-enables the creation of highly efficient drug delivery vehicles. Thus, this innovative approach not only simplifies medication regimens by significantly reducing the number of necessary doses but also minimizes the pill burden and associated treatment termination-issues associated with polypharmacy. It is important to bring forth the opportunities and challenges of this synergy between microfluidic-driven complex emulsions and multi-drug therapy poses. Together, they not only offer a sophisticated method for addressing the intricacies of delivering multiple drugs but also align with broader healthcare objectives of enhancing treatment outcomes, patient safety, and quality of life, underscoring the importance of dosage form innovations in tackling the multifaceted challenges of modern pharmacotherapy.

Fabrication of Perfluoropolyether Microfluidic Devices Using Laser Engraving for Uniform Droplet Production

A perfluoropolyether (PFPE)-based microfluidic device with cross-junction microchannels was fabricated with the purpose of producing uniform droplets. The microchannels were developed using CO2 laser engraving. PFPE was chosen as the main material because of its excellent solvent resistance. Polyethylene glycol diacrylate (PEGDA) was mixed with PFPE to improve the hydrophilic properties of the inner surface of the microchannels. The microchannels of the polydimethylsiloxane microfluidic device had a blackened and rough surface after laser engraving. By contrast, the inner surface of the microchannels of the PFPE-PEGDA microfluidic device exhibited a smooth surface. The lower power and faster speed of the laser engraving resulted in the development of microchannels with smaller dimensions, less than 30 μm in depth. The PFPE and PFPE-PEGDA microfluidic devices were used to produce uniform water and oil droplets, respectively. We believe that such a PFPE-based microfluidic device with CO2-laser-engraved microchannels can be used as a microfluidic platform for applications in various fields, such as biological and chemical analysis, extraction, and synthesis.

Development and future of droplet microfluidics

Over the past two decades, advances in droplet-based microfluidics have facilitated new approaches to process and analyze samples with unprecedented levels of precision and throughput. A wide variety of applications has been inspired across multiple disciplines ranging from materials science to biology. Understanding the dynamics of droplets enables optimization of microfluidic operations and design of new techniques tailored to emerging demands. In this review, we discuss the underlying physics behind high-throughput generation and manipulation of droplets. We also summarize the applications in droplet-derived materials and droplet-based lab-on-a-chip biotechnology. In addition, we offer perspectives on future directions to realize wider use of droplet microfluidics in industrial production and biomedical analyses.

Multichannel Multijunction Droplet Microfluidic Device to Synthesize Hydrogel Microcapsules with Different Core-Shell Structures and Adjustable Core Positions

Core-shell hydrogel microcapsules have sparked great interest due to their unique characteristics and prospective applications in the medical, pharmaceutical, and cosmetic fields. However, complex synthetic procedures and expensive costs have limited their practical application. Herein, we designed and prepared several multichannel and multijunctional droplet microfluidic devices based on soft lithography for the effective synthesis of core-shell hydrogel microcapsules for different purposes. Additionally, two different cross-linking processes (ultraviolet (UV) exposure and interfacial polymerization) were used to synthesize different types of core-shell structured hydrogel microcapsules. Hydrogel microcapsules with gelatin methacryloyl (GelMA) as the core and polyacrylamide (PAM) as the thin shell were synthesized using UV cross-linking. Using an interfacial polymerization process, another core-shell structured microcapsule with GelMA as the core and Ca2+ cross-linked alginate with polyethylenimine (PEI) as the shell was constructed, and the core diameter and total droplet diameter were flexibly controlled by carving. Noteworthy, these hydrogel microcapsules exhibit stimuli-responsiveness and controlled release ability. Overall, a novel technique was developed to successfully synthesize various hydrogel microcapsules with core-shell microstructures. The hydrogel microcapsules possess a multilayered structure that facilitates the coassembly of cells and drugs, as well as the layered assembly of multiple drugs, to develop synergistic therapeutic regimens. These adaptable and controllable hydrogel microdroplets shall held great promise for multicell or multidrug administration as well as for high-throughput drug screening.

Microfluidics-mediated Liposomal Nanoparticles for Cancer Therapy: Recent Developments on Advanced Devices and Technologies

Liposomes, spherical particles with phospholipid double layers, have been extensively studied over the years as a means of drug administration. Conventional manufacturing techniques like thin-film hydration and extrusion have limitations in controlling liposome size and distribution. Microfluidics enables superior tuning of parameters during the self-assembly of liposomes, producing uniform populations. This review summarizes microfluidic methods for engineering liposomes, including hydrodynamic flow focusing, jetting, micro mixing, and double emulsions. The precise control over size and lamellarity afforded by microfluidics has advantages for cancer therapy. Liposomes created through microfluidics and designed to encapsulate chemotherapy drugs have exhibited several advantageous properties in cancer treatment. They showcase enhanced permeability and retention effects, allowing them to accumulate specifically in tumor tissues passively. This passive targeting of tumors results in improved drug delivery and efficacy while reducing systemic toxicity. Promising results have been observed in pancreatic, lung, breast, and ovarian cancer models, making them a potential breakthrough in cancer therapy. Surface-modified liposomes, like antibodies or carbohydrates, also achieve active targeting. Overall, microfluidic fabrication improves reproducibility and scalability compared to traditional methods while maintaining drug loading and biological efficacy. Microfluidics-engineered liposomal formulations hold significant potential to overcome challenges in nanomedicine-based cancer treatment.

Phase Change Materials Meet Microfluidic Encapsulation

Improving the utilization of thermal energy is crucial in the world nowadays due to the high levels of energy consumption. One way to achieve this is to use phase change materials (PCMs) as thermal energy storage media, which can be used to regulate temperature or provide heating/cooling in various applications. However, PCMs have limitations like low thermal conductivity, leakage, and corrosion. To overcome these challenges, PCMs are encapsulated into microencapsulated phase change materials (MEPCMs) capsules/fibers. This encapsulation prevents PCMs from leakage and corrosion issues, and the microcapsules/fibers act as conduits for heat transfer, enabling efficient exchange between the PCM and its surroundings. Microfluidics-based MEPCMs have attracted intensive attention over the past decade due to the exquisite control over flow conditions and size of microcapsules. This review paper aims to provide an overview of the state-of-art progress in microfluidics-based encapsulation of PCMs. The principle and method of preparing MEPCM capsules/fibers using microfluidic technology are elaborated, followed by the analysis of their thermal and microstructure characteristics. Meanwhile, the applications of MEPCM in the fields of building energy conservation, textiles, military aviation, solar energy utilization, and bioengineering are summarized. Finally, the perspectives on MEPCM capsules/fibers are discussed.

Facile and Programmable Capillary-Induced Assembly of Prototissues via Hanging Drop Arrays

An important goal for bottom-up synthetic biology is to construct tissue-like structures from artificial cells. The key is the ability to control the assembly of the individual artificial cells. Unlike most methods resorting to external fields or sophisticated devices, inspired by the hanging drop method used for culturing spheroids of biological cells, we employ a capillary-driven approach to assemble giant unilamellar vesicles (GUVs)-based protocells into colonized prototissue arrays by means of a coverslip with patterned wettability. By spatially confining and controllably merging a mixed population of lipid-coated double-emulsion droplets that hang on a water/oil interface, an array of synthetic tissue-like constructs can be obtained. Each prototissue module in the array comprises multiple tightly packed droplet compartments where interfacial lipid bilayers are self-assembled at the interfaces both between two neighboring droplets and between the droplet and the external aqueous environment. The number, shape, and composition of the interconnected droplet compartments can be precisely controlled. Each prototissue module functions as a processer, in which fast signal transports of molecules via cell-cell and cell-environment communications have been demonstrated by molecular diffusions and cascade enzyme reactions, exhibiting the ability to be used as biochemical sensing and microreactor arrays. Our work provides a simple yet scalable and programmable method to form arrays of prototissues for synthetic biology, tissue engineering, and high-throughput assays.

Sunset Yellow Confined in Curved Geometry: A Microfluidic Approach

The behavior of lyotropic chromonic liquid crystals (LCLCs) in confined environments is an interesting research field that still awaits exploration, with multiple key variables to be uncovered and understood. Microfluidics is a highly versatile technique that allows us to confine LCLCs in micrometric spheres. As microscale networks offer distinct interplays between the surface effects, geometric confinement, and viscosity parameters, rich and unique interactions emerging at the LCLC-microfluidic channel interfaces are expected. Here, we report on the behavior of pure and chiral doped nematic Sunset Yellow (SSY) chromonic microdroplets produced through a microfluidic flow-focusing device. The continuous production of SSY microdroplets with controllable size gives the possibility to systematically study their topological textures as the function of their diameters. Indeed, doped SSY microdroplets produced via microfluidics, show topologies that are typical of common chiral thermotropic liquid crystals. Furthermore, few droplets exhibit a peculiar texture never observed for chiral chromonic liquid crystals. Finally, the achieved precise control of the produced LCLC microdroplets is a crucial step for technological applications in biosensing and anticounterfeiting.

Microfluidic devices for the detection of disease-specific proteins and other macromolecules, disease modelling and drug development: A review

Microfluidics is a revolutionary technology that has promising applications in the biomedical field.Integrating microfluidic technology with the traditional assays unravels the innumerable possibilities for translational biomedical research. Microfluidics has the potential to build up a novel platform for diagnosis and therapy through precise manipulation of fluids and enhanced throughput functions. The developments in microfluidics-based devices for diagnostics have evolved in the last decade and have been established for their rapid, effective, accurate and economic advantages. The efficiency and sensitivity of such devices to detect disease-specific macromolecules like proteins and nucleic acids have made crucial impacts in disease diagnosis. The disease modelling using microfluidic systems provides a more prominent replication of the in vivo microenvironment and can be a better alternative for the existing disease models. These models can replicate critical microphysiology like the dynamic microenvironment, cellular interactions, and biophysical and biochemical cues. Microfluidics also provides a promising system for high throughput drug screening and delivery applications. However, microfluidics-based diagnostics still encounter related challenges in the reliability, real-time monitoring and reproducibility that circumvents this technology from being impacted in the healthcare industry. This review highlights the recent microfluidics developments for modelling and diagnosing common diseases, including cancer, neurological, cardiovascular, respiratory and autoimmune disorders, and its applications in drug development.

Microfluidic Manipulation for Biomedical Applications in the Central and Peripheral Nervous Systems

Physical injuries and neurodegenerative diseases often lead to irreversible damage to the organizational structure of the central nervous system (CNS) and peripheral nervous system (PNS), culminating in physiological malfunctions. Investigating these complex and diverse biological processes at the macro and micro levels will help to identify the cellular and molecular mechanisms associated with nerve degeneration and regeneration, thereby providing new options for the development of new therapeutic strategies for the functional recovery of the nervous system. Due to their distinct advantages, modern microfluidic platforms have significant potential for high-throughput cell and organoid cultures in vitro, the synthesis of a variety of tissue engineering scaffolds and drug carriers, and observing the delivery of drugs at the desired speed to the desired location in real time. In this review, we first introduce the types of nerve damage and the repair mechanisms of the CNS and PNS; then, we summarize the development of microfluidic platforms and their application in drug carriers. We also describe a variety of damage models, tissue engineering scaffolds, and drug carriers for nerve injury repair based on the application of microfluidic platforms. Finally, we discuss remaining challenges and future perspectives with regard to the promotion of nerve injury repair based on engineered microfluidic platform technology.

Scalable fabrication, compartmentalization and applications of living microtissues

Living microtissues are used in a multitude of applications as they more closely resemble native tissue physiology, as compared to 2D cultures. Microtissues are typically composed of a combination of cells and materials in varying combinations, which are dictated by the applications' design requirements. Their applications range wide, from fundamental biological research such as differentiation studies to industrial applications such as cruelty-free meat production. However, their translation to industrial and clinical settings has been hindered due to the lack of scalability of microtissue production techniques. Continuous microfluidic processes provide an opportunity to overcome this limitation as they offer higher throughput production rates as compared to traditional batch techniques, while maintaining reproducible control over microtissue composition and size. In this review, we provide a comprehensive overview of the current approaches to engineer microtissues with a focus on the advantages of, and need for, the use of continuous processes to produce microtissues in large quantities. Finally, an outlook is provided that outlines the required developments to enable large-scale microtissue fabrication using continuous processes.

W/o/w multiple emulsions: A novel trend in functional ice cream preparations?

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The possible applications of w/o/w multiple emulsions (MEs) in ice creams are described.

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W/o/w MEs enable the encapsulation of sensitive compounds.

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Fat content is reduced using w/o/w MEs without losing the creaminess of the final products.

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Ice cream is a very suitable matrix for application of Pickering emulsions.

Ice cream is a popular product worldwide. Unfortunatelly, it contains a significant amount of fat. In this review, promising strategies for the use of w/o/w multiple emulsion structures in creams are assessed. W/o/w multiple emulsions (MEs) enable reduction the fat without losing the creamy taste and mouthfeel and also encapsulation of sensitive compounds. The encouraging application and formation of MEs in ice cream mixtures is supported by the use of natural food ingredients, such as fiber, which helps to stabilize the whole system and improves nutritional value. The future trends may be focused on the target stabilizations using Pickering paticles (PPs). The possible advantages, manufacture, evaluation methods, and predicted future prospects of MEs in ice creams are discussed.

Microgels based on 0D-3D carbon materials: Synthetic techniques, properties, applications, and challenges

Microgels are three-dimensional (3D) colloidal hydrogel particles with outstanding features such as biocompatibility, good mechanical properties, tunable sizes from submicrometer to tens of nanometers, and large surface areas. Because of these unique qualities, microgels have been widely used in various applications. Carbon-based materials (CMs) with various dimensions (0-3D) have recently been investigated as promising candidates for the design and fabrication of microgels because of their large surface area, excellent conductivity, unique chemical stability, and low cost. Here, we provide a critical review of the specific characteristics of CMs that are being incorporated into microgels, as well as the state-of-the art applications of CM-microgels in pollutant adsorption and photodegradation, H₂ evoluation, CO₂ capture, soil conditioners, water retention, drug delivery, cell encapsulation, and tissue engineering. Advanced preparation techniques for CM-microgel systems are also summarized and discussed. Finally, challenges related to the low colloidal stability of CM-microgels and development strategies are examined. This review shows that CM-microgels have the potential to be widely used in various practical applications.

Designable Micro-/Nano-Structured Smart Polymeric Materials

Smart polymeric materials with dynamically tunable physico-chemical characteristics in response to changes of environmental stimuli, have received considerable attention in myriad fields. The diverse combination of their micro-/nano-structural and molecular designs creates promising and exciting opportunities for exploiting advanced smart polymeric materials. Engineering micro-/nano-structures into smart polymeric materials with elaborate molecular design enables intricate coordination between their structures and molecular-level response to cooperatively realize smart functions for practical applications. In this review, recent progresses of smart polymeric materials that combine micro-/nano-structures and molecular design to achieve designed advanced functions are highlighted. Smart hydrogels, gating membranes, gratings, milli-particles, micro-particles and microvalves are employed as typical examples to introduce their design and fabrication strategies. Meanwhile, the key roles of interplay between their micro-/nano-structures and responsive properties to realize the desired functions for their applications are emphasized. Finally, perspectives on the current challenges and opportunities of micro-/nano-structured smart polymeric materials for their future development are presented.

Recent Advances in Drug Delivery System Fabricated by Microfluidics for Disease Therapy

Traditional drug therapy faces challenges such as drug distribution throughout the body, rapid degradation and excretion, and extensive adverse reactions. In contrast, micro/nanoparticles can controllably deliver drugs to target sites to improve drug efficacy. Unlike traditional large-scale synthetic systems, microfluidics allows manipulation of fluids at the microscale and shows great potential in drug delivery and precision medicine. Well-designed microfluidic devices have been used to fabricate multifunctional drug carriers using stimuli-responsive materials. In this review, we first introduce the selection of materials and processing techniques for microfluidic devices. Then, various well-designed microfluidic chips are shown for the fabrication of multifunctional micro/nanoparticles as drug delivery vehicles. Finally, we describe the interaction of drugs with lymphatic vessels that are neglected in organs-on-chips. Overall, the accelerated development of microfluidics holds great potential for the clinical translation of micro/nanoparticle drug delivery systems for disease treatment.

One-step emulsification for controllable preparation of ethyl cellulose microcapsules and their sustained release performance

A simple and versatile strategy for controlled production of monodisperse ethyl cellulose (EC) microcapsules by a single-stage emulsification method has been developed. Monodisperse oil-in-water emulsions, obtained by a microfluidic device, are used as templates for preparing EC microcapsules. Oil-soluble ethyl acetate (EA) is miscible with water, so the interfacial mass transfer between EA and water occurs sufficiently, which leads to water molecules pass through the phase interface and diffuse into emulsion interior. Water molecules aggregate at the interface, and some merge into a large water drop in the central position of the emulsion. After evaporation of EA solvent, monodisperse EC microcapsules create large numbers of pits on the surface with a hollow structure. Curcumin is used as a model drug and embedded in the hollow structure. EC microcapsules have good, sustained drug release efficacy in a simulated intestinal environment, and the release process of EC microcapsules containing 6.14% drug-loaded capacity is fully consistent with the vitro drug release model. Such simple techniques for making EC microcapsules may open a window to the controlled preparation of other multifunctional microcapsules. Besides, it offers theoretical guidance for the study of EC microcapsules as drug carriers and expanding clinical application of curcumin.

Microfluidic Tissue Engineering and Bio-Actuation

Bio-hybrid technologies aim to replicate the unique capabilities of biological systems that could surpass advanced artificial technologies. Soft bio-hybrid robots consist of synthetic and living materials and have the potential to self-assemble, regenerate, work autonomously, and interact safely with other species and the environment. Cells require a sufficient exchange of nutrients and gases, which is guaranteed by convection and diffusive transport through liquid media. The functional development and long-term survival of biological tissues in vitro can be improved by dynamic flow culture, but only microfluidic flow control can develop tissue with fine structuring and regulation at the microscale. Full control of tissue growth at the microscale will eventually lead to functional macroscale constructs, which are needed as the biological component of soft bio-hybrid technologies. This review summarizes recent progress in microfluidic techniques to engineer biological tissues, focusing on the use of muscle cells for robotic bio-actuation. Moreover, the instances in which bio-actuation technologies greatly benefit from fusion with microfluidics are highlighted, which include: the microfabrication of matrices, biomimicry of cell microenvironments, tissue maturation, perfusion, and vascularization.

Synthetic Cells: From Simple Bio-Inspired Modules to Sophisticated Integrated Systems

Bottom-up synthetic biology is the science of building systems that mimic the structure and function of living cells from scratch. To do this, researchers combine tools from chemistry, materials science, and biochemistry to develop functional and structural building blocks to construct synthetic cell-like systems. The many strategies and materials that have been developed in recent decades have enabled scientists to engineer synthetic cells and organelles that mimic the essential functions and behaviors of natural cells. Examples include synthetic cells that can synthesize their own ATP using light, maintain metabolic reactions through enzymatic networks, perform gene replication, and even grow and divide. In this Review, we discuss recent developments in the design and construction of synthetic cells and organelles using the bottom-up approach. Our goal is to present representative synthetic cells of increasing complexity as well as strategies for solving distinct challenges in bottom-up synthetic biology.

Gradient Printing Alginate Herero Gel Microspheres for Three-Dimensional Cell Culture

Hydrogel microspheres are widely used in tissue engineering, such as 3D cell culture and injection therapy, and among which, heterogeneous microspheres are drawing much attention as a promising tool to carry multiple cell types in separated phases. However, it is still a big challenge to fabricate heterogeneous gel microspheres with excellent resolution and different material components in limited sizes. Here, we developed a multi-channel dynamic micromixer, which can use active mechanical mixing to achieve rapid mixing with multi-component materials and extrude the homogenized material. By changing the flow rate ratio of the solutions of the two components and by rapidly mixing in the micromixer, real-time concentration change of the mixed material at the outlet could be monitored in a process so-called “gradient printing”. By studying the mixing efficiency of the micromixer, its size and process parameters were optimized. Using the novel dynamic gradient printing method, the composition of the hydrogel microspheres can be distributed in any proportion and alginate heterogeneous gel microspheres with adjustable cell concentration were fabricated. The effects of cell concentration on cell viability and proliferation ability under three-dimensional culture conditions were also studied. The results showed that cells have very low death rate and can exchange substances within the microspheres. Due to the micromixing ability of the micromixers, the demand for biological reagents and materials such as cells, proteins, cytokines and other materials could be greatly reduced, which helps reduce the experimental cost and improve the feasibility of the method in practical use. The heterogeneous gel microsphere can be greatly valuable for research in various fields such as analytical chemistry, microarray, drug screening, and tissue culture.

A Mild Method for Encapsulation of Citral in Monodispersed Alginate Microcapsules

Citral is a typical UV-irritation and acid-sensitive active and here we develop a mild method for the encapsulation of citral in calcium alginate microcapsules, in which UV irritation or acetic acid is avoided. Monodispersed oil-in-water-in-oil (O/W/O) emulsions are generated in a capillary microfluidic device as precursors. The middle aqueous phase of O/W/O emulsions contains sodium alginate, calcium-ethylenediaminetetraacetic acid (EDTA-Ca) complex as the calcium source, and D-(+)-Gluconic acid δ-lactone (GDL) as the acidifier. Hydrolysis of GDL will decrease the pH value of the middle aqueous solution, which will trigger the calcium ions released from the EDTA-Ca complex to cross-link with alginate molecules. After the gelling process, the O/W/O emulsions will convert to alginate microcapsules with a uniform structure and monodispersed size. The preparation conditions for alginate microcapsules are optimized, including the constituent concentration in the middle aqueous phase of O/W/O emulsions and the mixing manner of GDL with the alginate-contained aqueous solution. Citral-containing alginate microcapsules are successfully prepared by this mild method and the sustained-release characteristic of citral from alginate microcapsules is analyzed. Furthermore, a typical application of citral-containing alginate microcapsules to delay the oxidation of oil is also demonstrated. The mild gelling method provides us a chance to encapsulate sensitive hydrophobic actives with alginate, which takes many potential applications in pharmaceutical, food, and cosmetic areas.

From dynamic self-organization to avalanching instabilities in soft-granular threads

We study the dynamics of threads of monodisperse droplets, including droplet chains and multi-chains, in which the droplets are interconnected by capillary bridges of another immiscible liquid phase. This system represents wet soft-granular matter - a class of granular materials in which the grains are soft and wetted by thin fluid films-with other examples including wet granular hydrogels or foams. In contrast to wet granular matter with rigid grains (e.g., wet sand), studied previously, the deformability of the grains raises the number of available metastable states and facilitates rearrangements which allow for reorganization and self-assembly of the system under external drive, e.g., applied via viscous forces. We use a co-flow configuration to generate a variety of unique low-dimensional regular granular patterns, intermediate between 1D and 2D, ranging from linear chains and chains with periodically occurring folds to multi-chains and segmented structures including chains of finite length. In particular, we observe that the partially folded chains self-organize via limit cycle of displacements and rearrangements occurring at a frequency self-adapted to the rate of build-up of compressive strain in the chain induced by the viscous forces. Upon weakening of the capillary arrest of the droplets, we observe spontaneous fluidization of the quasi-solid structures and avalanches of rearrangements. We identify two types of fluidization-induced instabilities and rationalize them in terms of a competition between advection and propagation. While we use aqueous droplets as the grains we demonstrate that the reported mechanisms of adaptive self-assembly apply to other types of soft granular systems including foams and microgels. We discuss possible application of the reported quasi-1D compartmentalized structures in tissue engineering, bioprinting and materials science.

Materials and methods for droplet microfluidic device fabrication

Since the first reports two decades ago, droplet-based systems have emerged as a compelling tool for microbiological and (bio)chemical science, with droplet flow providing multiple advantages over standard single-phase microfluidics such as removal of Taylor dispersion, enhanced mixing, isolation of droplet contents from surfaces, and the ability to contain and address individual cells or biomolecules. Typically, a droplet microfluidic device is designed to produce droplets with well-defined sizes and compositions that flow through the device without interacting with channel walls. Successful droplet flow is fundamentally dependent on the microfluidic device - not only its geometry but moreover how the channel surfaces interact with the fluids. Here we summarise the materials and fabrication techniques required to make microfluidic devices that deliver controlled uniform droplet flow, looking not just at physical fabrication methods, but moreover how to select and modify surfaces to yield the required surface/fluid interactions. We describe the various materials, surface modification techniques, and channel geometry approaches that can be used, and give examples of the decision process when determining which material or method to use by describing the design process for five different devices with applications ranging from field-deployable chemical analysers to water-in-water droplet creation. Finally we consider how droplet microfluidic device fabrication is changing and will change in the future, and what challenges remain to be addressed in the field.

The creation of raspberry-like droplets and their coalescence dynamics: An ideal model for certain biological processes

HYPOTHESIS

Although a raspberry-like configuration has been long observed in biological processes (e.g., the intimate association between Cajal bodies and B-snurposomes), studies on this morphology are very limited. Raspberry-like droplets created with multiple immiscible liquids are expected to provides an ideal model for such structures in biological systems, including their possible formation mechanism, phase behaviors, and coalescence dynamics.

EXPERIMENTS & SIMULATIONS

Using three liquid phases, one surfactant and some colloidal particles, raspberry-like droplets containing one large central droplet and multiple protrusions embedded on its surface were successfully created. Confocal microscopy studies were carried out to track their formation and coalescence dynamics. A 2D phase-field model was applied to test the influence of the protrusions in the system.

FINDINGS

The formation of this raspberry-like morphology involves a partial inversion process, which was predicted by Friberg et al. with numerical simulations but has never been demonstrated experimentally. A two-step coalescence was revealed, where the protrusions merge first and create a capillary bridge, which drives the droplets to coalesce. Increasing the viscosity of the continuous phase can help to prevent the destabilization. These fundamental features of raspberry-like droplets represent an important step toward producing multi-liquid materials with unique functionality, and can potentially illuminate some biological systems and processes.

An outlook on microfluidics: the promise and the challenge

This perspective considers ways in which the field of microfluidics can increase its impact by improving existing technologies and enabling new functionalities. We highlight applications where microfluidics has made or can make important contributions, including diagnostics, food safety, and the production of materials. The success of microfluidics assumes several forms, including fundamental innovations in fluid mechanics that enable the precise manipulation of fluids at small scales and the development of portable microfluidic chips for commercial purposes. We identify outstanding technical challenges whose resolution could increase the accessibility of microfluidics to users with both scientific and non-technical backgrounds. They include the simplification of procedures for sample preparation, the identification of materials for the production of microfluidic devices in both laboratory and commercial settings, and the replacement of auxiliary equipment with automated components for the operation of microfluidic devices.

Cell encapsulation in alginate-based microgels using droplet microfluidics; a review on gelation methods and applications

Cell encapsulation within the microspheres using a semi-permeable polymer allows the two-way transfer of molecules such as oxygen, nutrients, and growth factors. The main advantages of cell encapsulation technology include controlling the problems involved in transplanting rejection in tissue engineering applications and reducing the long-term need for immunosuppressive drugs following organ transplantation to eliminate the side effects. Cell-laden microgels can also be used in 3D cell cultures, wound healing, and cancerous clusters for drug testing. Since cell encapsulation is used for different purposes, several techniques have been developed to encapsulate cells. Droplet-based microfluidics is one of the most valuable techniques in cell encapsulating. This study aimed to review the geometries and the mechanisms proposed in microfluidic systems to precisely control cell-laden microgels production with different biopolymers. We also focused on alginate gelation techniques due to their essential role in cell encapsulation applications. Finally, some applications of these microgels and researches will be explored.

Droplet microfluidics-based biomedical microcarriers

Droplet microfluidic technology provides a new platform for controllable generation of microdroplets and droplet-derived materials. In particular, because of the ability in high-throughput production and accurate control of the size, structure, and function of these materials, droplet microfluidics presents unique advantages in the preparation of functional microcarriers, i.e., microsized liquid containers or solid particles that serve as substrates of biomolecules or cells. These microcarriers could be extensively applied in the areas of cell culture, tissue engineering, and drug delivery. In this review, we focus on the fabrication of microcarriers from droplet microfluidics, and discuss their applications in the biomedical field. We start with the basic principle of droplet microfluidics, including droplet generation regimes and its control methods. We then introduce the fabrication of biomedical microcarriers based on single, double, and multiple emulsion droplets, and emphasize the various applications of microcarriers in biomedical field, especially in 3D cell culture, drug development and biomedical detection. Finally, we conclude this review by discussing the limitations and challenges of droplet microfluidics in preparing microcarriers. STATEMENT OF SIGNIFICANCE: Because of its precise control and high throughput, droplet microfluidics has been employed to generate functional microcarriers, which have been widely used in the areas of drug development, tissue engineering, and regenerative medicine. This review is significant because it emphasizes recent progress in research on droplet microfluidics in the preparation and application of biomedical microcarriers. In addition, this review suggests research directions for the future development of biomedical microcarriers based on droplet microfluidics by presenting existing shortcomings and challenges.

Core-shell microparticles: From rational engineering to diverse applications

Core-shell microparticles, composed of solid, liquid, or gas bubbles surrounded by a protective shell, are gaining considerable attention as intelligent and versatile carriers that show great potential in biomedical fields. In this review, an overview is given of recent developments in design and applications of biodegradable core-shell systems. Several emerging methodologies including self-assembly, gas-shearing, and coaxial electrospray are discussed and microfluidics technology is emphasized in detail. Furthermore, the characteristics of core-shell microparticles in artificial cells, drug release and cell culture applications are discussed and the superiority of these advanced multi-core microparticles for the generation of artificial cells is highlighted. Finally, the respective developing orientations and limitations inherent to these systems are addressed. It is hoped that this review can inspire researchers to propel the development of this field with new ideas.

Microfluidic fabrication of hydrogel microparticles with MOF-armoured multi-enzymes for cascade biocatalytic reactions

Uniform hydrogel microparticles with ZIF-8 nanoparticles for molecular co-confinement of cascade enzymes are developed by microfluidics to achieve enhanced stability and reusability under harsh conditions.

Dynamics of polydisperse multiple emulsions in microfluidic channels

Multiple emulsions are a class of soft fluid in which small drops are immersed within a larger one and stabilized over long periods of time by a surfactant. We recently showed that, if a monodisperse multiple emulsion is subject to a pressure-driven flow, a wide variety of nonequilibrium steady states emerges at late times, whose dynamics relies on a complex interplay between hydrodynamic interactions and multibody collisions among internal drops. In this work, we use lattice Boltzmann simulations to study the dynamics of polydisperse double emulsions driven by a Poiseuille flow within a microfluidic channel. Our results show that their behavior is critically affected by multiple factors, such as initial position, polydispersity index, and area fraction occupied within the emulsion. While at low area fraction inner drops may exhibit either a periodic rotational motion (at low polydispersity) or arrange into nonmotile configurations (at high polydispersity) located far from each other, at larger values of area fraction they remain in tight contact and move unidirectionally. This decisively conditions their close-range dynamics, quantitatively assessed through a time-efficiency-like factor. Simulations also unveil the key role played by the capsule, whose shape changes can favor the formation of a selected number of nonequilibrium states in which both motile and nonmotile configurations are found.

An overview of the production methods for core-shell microspheres for parenteral controlled drug delivery

Core-shell microspheres hold great promise as a drug delivery system because they offer several benefits over monolithic microspheres in terms of release kinetics, for instance a reduced initial burst release, the possibility of delayed (pulsatile) release, and the possibility of dual-drug release. Also, the encapsulation efficiency can significantly be improved. Various methods have proven to be successful in producing these core-shell microspheres, both the conventional bulk emulsion solvent evaporation method and methods in which the microspheres are produced drop by drop. The latter have become increasingly popular because they provide improved control over the particle characteristics. This review assesses various production methods for core-shell microspheres and summarizes the characteristics of formulations prepared by the different methods, with a focus on their release kinetics.

Microfluidic droplet-based functional materials for cell manipulation

Functional materials from the microfluidic-based droplet community are emerging as enabling tools for various applications in tissue engineering and cell biology. The innovative micro- and nano-scale materials with diverse sizes, shapes and components can be fabricated without the use of complicated devices, allowing unprecedented control over the cells that interact with them. Here, we review the current development of microfluidic-based droplet techniques for creation of functional materials (i.e., liquid droplet, microcapsule, and microparticle). We also describe their various applications for manipulating cell fate and function.

Single-Cell Microgels for Diagnostics and Therapeutics

Cell encapsulation within hydrogel droplets is transforming what is feasible in multiple fields of biomedical science such as tissue engineering and regenerative medicine, in vitro modeling, and cell-based therapies. Recent advances have allowed researchers to miniaturize material encapsulation complexes down to single-cell scales, where each complex, termed a single-cell microgel, contains only one cell surrounded by a hydrogel matrix while remaining <100 μm in size. With this achievement, studies requiring single-cell resolution are now possible, similar to those done using liquid droplet encapsulation. Of particular note, applications involving long-term in vitro cultures, modular bioinks, high-throughput screenings, and formation of 3D cellular microenvironments can be tuned independently to suit the needs of individual cells and experimental goals. In this progress report, an overview of established materials and techniques used to fabricate single-cell microgels, as well as insight into potential alternatives is provided. This focused review is concluded by discussing applications that have already benefited from single-cell microgel technologies, as well as prospective applications on the cusp of achieving important new capabilities.

Nanotechnology Based Approaches in Phage Therapy: Overcoming the Pharmacological Barriers

With the emergence and spread of global antibiotic resistance and the need for searching safer alternatives, there has been resurgence in exploring the use of bacteriophages in the treatment of bacterial infections referred as phage therapy. Although modern phage therapy has come a long way as demonstrated by numerous efficacy studies but the fact remains that till date, phage therapy has not received regulatory approval for human use (except for compassionate use).Thus, to hit the clinical market, the roadblocks need to be seriously addressed and gaps mended with modern solution based technologies. Nanotechnology represents one such ideal and powerful tool for overcoming the pharmacological barriers (low stability, poor in-vivo retention, targeted delivery, neutralisation by immune system etc.) of administered phage preparations.In literature, there are many review articles on nanotechnology and bacteriophages but these are primarily focussed on highlighting the use of lytic and temperate phages in different fields of nano-medicine such as nanoprobes, nanosensors, cancer diagnostics, cancer cell targeting, drug delivery through phage receptors, phage display etc. Reviews specifically focused on the use of nanotechnology driven techniques strictly to improve phage therapy are however limited. Moreover, these review if present have primarily focussed on discussing encapsulation as a primary method for improving the stability and retention of phage(s) in the body.With new advances made in the field of nanotechnology, approaches extend from mere encapsulation to recently adopted newer strategies. The present review gives a detailed insight into the more recent strategies which include 1) use of lipid based nano-carriers (liposomes, transfersomes etc.) 2) adopting microfluidic based approach, surface modification methods to further enhance the efficiency and stability of phage loaded liposomes 3) Nano- emulsification approach with integration of microfluidics for producing multiple emulsions (suitable for phage cocktails) with unique control over size, shape and drop morphology 4) Phage loaded nanofibers produced by electro-spinning and advanced core shell nanofibers for immediate, biphasic and delayed release systems and 5) Smart release drug delivery platforms that allow superior control over dosing and phage release as and when required. All these new advances are aimed at creating a suitable housing system for therapeutic bacteriophage preparations while targeting the multiple issues of phage therapy i.e., improving phage stability and titers, improving in-vivo retention times, acting as suitable delivery systems for sustained release at target site of infection, improved penetration into biofilms and protection from immune cell attack. The present review thus aims at giving a complete insight into the recent advances (2010 onwards) related to various nanotechnology based approaches to address the issues pertaining to phage therapy. This is essential for improving the overall therapeutic index and success of phage therapy for future clinical approval.

Emulsion Designer Using Microfluidic Three-Dimensional Droplet Printing in Droplet

Hierarchical emulsions are interesting for both scientific researches and practical applications. Hierarchical emulsions prepared by microfluidics require complicated device geometry and delicate control of flow rates. Here, a versatile method is developed to design hierarchical emulsions using microfluidic 3D droplet printing in droplet. The process of droplet printing in droplet mimics the dragonfly laying eggs and has advantages of easy processing and flexible design. To demonstrate the capability of the method, double emulsions and triple emulsions with tunable core number, core size, and core composition are prepared. The hierarchical emulsions are excellent templates for the developments of functional materials. Flattened crescent-moon-shaped particles are then fabricated using double emulsions printed in confined 2D space as templates. The particles are excellent delivery vehicles for 2D interfaces, which can load and transport cargos through a well-defined trajectory under external magnetic steering. Microfluidic 3D droplet printing in droplet provides a powerful platform with improved simplicity and flexibility for the design of hierarchical emulsions and functional materials.

Influence of Microgel Fabrication Technique on Granular Hydrogel Properties

Bulk hydrogels traditionally used for tissue engineering and drug delivery have numerous limitations, such as restricted injectability and a nanoscale porosity that reduces cell invasion and mass transport. An evolving approach to address these limitations is the fabrication of hydrogel microparticles (i.e., "microgels") that can be assembled into granular hydrogels. There are numerous methods to fabricate microgels; however, the influence of the fabrication technique on granular hydrogel properties is unexplored. Herein, we investigated the influence of three microgel fabrication techniques (microfluidic devices (MD), batch emulsions (BE), and mechanical fragmentation by extrusion (EF)) on the resulting granular hydrogel properties (e.g., mechanics, porosity, and injectability). Hyaluronic acid (HA) modified with various reactive groups (i.e., norbornenes (NorHA), pentenoates (HA-PA), and methacrylates (MeHA)) were used to form microgels with an average diameter of ∼100 μm. The MD method resulted in homogeneous spherical microgels, the BE method resulted in heterogeneous spherical microgels, and the EF method resulted in heterogeneous polygonal microgels. Across the various reactive groups, microgels fabricated with the MD and BE methods had lower functional group consumption when compared to microgels fabricated with the EF method. When microgels were jammed into granular hydrogels, the storage modulus (G') of EF granular hydrogels (∼1000-3000 Pa) was consistently an order of magnitude higher than G' for MD and BE granular hydrogels (∼50-200 Pa). Void space was comparable across all groups, although EF granular hydrogels exhibited an increased number of pores and decreased average pore size when compared to MD and BE granular hydrogels. Furthermore, granular hydrogel properties were tuned by varying the amount of cross-linker used during microgel fabrication. Lastly, granular hydrogels were injectable across formulations due to their general shear-thinning and self-healing properties. Taken together, this work thoroughly characterizes the influence of the microgel fabrication technique on granular hydrogel properties to inform the design of future systems for biomedical applications.

Synthesis of Polymer Janus Particles with Tunable Wettability Profiles as Potent Solid Surfactants to Promote Gas Delivery in Aqueous Reaction Media

Janus particles exhibit a strong tendency to directionally assemble and segregate to interfaces and thus offer advantages as colloidal analogues of molecular surfactants to improve the stability of multiphasic mixtures. Investigation and application of the unique adsorption properties require synthetic procedures that enable careful design and reliable control over the particles' asymmetric chemistry and wettability profiles with high morphological uniformity across a sample. Herein, we report on a novel one-step synthetic approach for the generation of amphiphilic polymer Janus particles with highly uniform and tunable wettability contrasts, which is based on using reconfigurable bi-phasic Janus emulsions as versatile particle scaffolds. Two phase-separated acrylate oils were used as the constituent droplet phases and transformed into their solidified Janus particle replicas via UV-induced radical polymerization. Using Janus emulsions as particle precursors offers the advantage that their internal droplet geometry can be fine-tuned by changing the force balance of surface tensions acting at the individual interfaces via surfactants or the volume ratio of the constituent phases. In addition, preassembled functional surfactants at the droplet interfaces can be locked in position upon polymerization, which enables both access toward postfunctionalization reaction schemes and the generation of highly uniform Janus particles with adjustable wettability profiles. Depending on the particle morphology and wettability, their interfacial position can be adjusted, which allows us to stabilize either air bubbles-in-water or water droplets-in-air (liquid marbles). Motivated by the interfacial activity of the particles and particularly the longevity of the resulting particle-stabilized air-in-water bubbles, we explored their ability to promote the delivery of oxygen inside a liquid-phase reaction medium, namely, for the heterogeneous Au-NP-mediated catalytic oxidation of d-glucose. We observed a 2.2-fold increase in the reaction rate attributed to the increase of the local concentration of oxygen around catalysts, thus showcasing a new strategy to overcome the limited solubility of gases in aqueous reaction media.

Microfluidics for Drug Development: From Synthesis to Evaluation

Drug development is a long process whose main content includes drug synthesis, drug delivery, and drug evaluation. Compared with conventional drug development procedures, microfluidics has emerged as a revolutionary technology in that it offers a miniaturized and highly controllable environment for bio(chemical) reactions to take place. It is also compatible with analytical strategies to implement integrated and high-throughput screening and evaluations. In this review, we provide a comprehensive summary of the entire microfluidics-based drug development system, from drug synthesis to drug evaluation. The challenges in the current status and the prospects for future development are also discussed. We believe that this review will promote communications throughout diversified scientific and engineering communities that will continue contributing to this burgeoning field.