A passive microfluidic system based on step emulsification allows the generation of libraries of nanoliter-sized droplets from microliter droplets of varying and known concentrations of a sample

Analysis of magnetic field-induced breakup of ferrofluid droplets in a symmetric Y-junction microchannel

This research focuses on the analysis of the breakup of ferrofluid droplets in a symmetric microchannel with a Y-junction microchannel, utilizing computational methods. The study proposes an innovative strategy to enhance the breakup phenomenon by introducing a magnetic field within the branches of the Y-junction microchannel. To verify the obtained results, a comprehensive comparison is conducted, incorporating previous numerical and experimental investigations available in the literature. The outcomes of this comparison demonstrate a significant concurrence between the current findings and the prior studies. The results unequivocally elucidate that the presence of a magnetic field accelerates the fragmentation of the parent droplet in comparison to scenarios without a magnetic field. Furthermore, it is established that the duration required for droplet breakup decreases as the magnetic Bond number increases. Achieved results indicates [Formula: see text] decreases about 3% and 1.5% for L*=3 and L*=4, respectively. It is worth highlighting that this trend is particularly accentuated in the case of smaller non-dimensional lengths, specifically L∗=3.0.

Tuna-step: tunable parallelized step emulsification for the generation of droplets with dynamic volume control to 3D print functionally graded porous materials

We present tuna-step, a novel microfluidic module based on step emulsification that allows for reliable generation of droplets of different sizes. Until now, sizes of droplets generated with step emulsification were hard-wired into the geometry of the step emulsification nozzle. To overcome this, we incorporate a thin membrane underneath the step nozzle that can be actuated by pressure, enabling the tuning of the nozzle size on-demand. By controllably reducing the height of the nozzle, we successfully achieved a three-order-of-magnitude variation in droplet volume without adjusting the flow rates of the two phases. We developed and applied a new hydrophilic surface modification, that ensured long-term stability and prevented swelling of the device when generating oil-in-water droplets. Our system produced functionally graded soft materials with adjustable porosity and material content. By combining our microfluidic device with a custom 3D printer, we generated and extruded oil-in-water emulsions in an agarose gel bath, creating unique self-standing 3D hydrogel structures with porosity decoupled from flow rate and with composition gradients of external phases. We upscaled tuna-step by setting 14 actuatable nozzles in parallel, offering a step-emulsification-based single chip solution that can accommodate various requirements in terms of throughput, droplet volumes, flow rates, and surface chemistry.

Gas-assisted microfluidic step-emulsification for generating micron- and submicron-sized droplets

Micron- and submicron-sized droplets have extensive applications in biomedical diagnosis and drug delivery. Moreover, accurate high-throughput analysis requires a uniform droplet size distribution and high production rates. Although the previously reported microfluidic coflow step-emulsification method can be used to generate highly monodispersed droplets, the droplet diameter (d) is constrained by the microchannel height (b), d ≳ 3 b , while the production rate is limited by the maximum capillary number of the step-emulsification regime, impeding emulsification of highly viscous liquids. In this paper, we report a novel, gas-assisted coflow step-emulsification method, where air serves as the innermost phase of a precursor hollow-core air/oil/water emulsion. Air gradually diffuses out, producing oil droplets. The size of the hollow-core droplets and the ultrathin oil layer thickness both follow the scaling laws of triphasic step-emulsification. The minimal droplet size attains d ≈ 1.7 b , inaccessible in standard all-liquid biphasic step-emulsification. The production rate per single channel is an order-of-magnitude higher than that in the standard all-liquid biphasic step-emulsification and is also superior to alternative emulsification methods. Due to low gas viscosity, the method can also be used to generate micron- and submicron-sized droplets of high-viscosity fluids, while the inert nature of the auxiliary gas offers high versatility.

Microfluidic Methods for Generation of Submicron Droplets: A Review

Submicron droplets are ubiquitous in nature and widely applied in fields such as biomedical diagnosis and therapy, oil recovery and energy conversion, among others. The submicron droplets are kinetically stable, their submicron size endows them with good mobility in highly constricted pathways, and the high surface-to-volume ratio allows effective loading of chemical components at the interface and good heat transfer performance. Conventional generation technology of submicron droplets in bulk involves high energy input, or relies on chemical energy released from the system. Microfluidic methods are widely used to generate highly monodispersed micron-sized or bigger droplets, while downsizing to the order of 100 nm was thought to be challenging because of sophisticated nanofabrication. In this review, we summarize the microfluidic methods that are promising for the generation of submicron droplets, with an emphasize on the device fabrication, operational condition, and resultant droplet size. Microfluidics offer a relatively energy-efficient and versatile tool for the generation of highly monodisperse submicron droplets.

Picoliter Droplet Generation and Dense Bead-in-Droplet Encapsulation via Microfluidic Devices Fabricated via 3D Printed Molds

Picoliter-scale droplets have many applications in chemistry and biology, such as biomolecule synthesis, drug discovery, nucleic acid quantification, and single cell analysis. However, due to the complicated processes used to fabricate microfluidic channels, most picoliter (pL) droplet generation methods are limited to research in laboratories with cleanroom facilities and complex instrumentation. The purpose of this work is to investigate a method that uses 3D printing to fabricate microfluidic devices that can generate droplets with sizes <100 pL and encapsulate single dense beads mechanistically. Our device generated monodisperse droplets as small as ~48 pL and we demonstrated the usefulness of this droplet generation technique in biomolecule analysis by detecting Lactobacillus acidophillus 16s rRNA via digital loop-mediated isothermal amplification (dLAMP). We also designed a mixer that can be integrated into a syringe to overcome dense bead sedimentation and found that the bead-in-droplet (BiD) emulsions created from our device had <2% of the droplets populated with more than 1 bead. This study will enable researchers to create devices that generate pL-scale droplets and encapsulate dense beads with inexpensive and simple instrumentation (3D printer and syringe pump). The rapid prototyping and integration ability of this module with other components or processes can accelerate the development of point-of-care microfluidic devices that use droplet-bead emulsions to analyze biological or chemical samples with high throughput and precision.

Easy-to-Operate Co-Flow Step Emulsification Device for High-Throughput Three-Dimensional Cell Culture

Cell culture plays an essential role in tissue engineering and high-throughput drug screening. Compared with two-dimensional (2D) in vitro culture, three-dimensional (3D) in vitro culture can mimic cells in vivo more accurately, including complex cellular organizations, heterogeneity, and cell–extracellular matrix (ECM) interactions. This article presents a droplet-based microfluidic chip that integrates cell distribution, 3D in vitro cell culture, and in situ cell monitoring in a single device. Using the microfluidic “co-flow step emulsification” approach, we have successfully prepared close-packed droplet arrays with an ultra-high-volume fraction (72%) which can prevent cells from adhering to the chip surface so as to achieve a 3D cell culture and make scalable and high-throughput cell culture possible. The proposed device could produce droplets from 55.29 ± 1.52 to 95.64 ± 3.35 μm, enabling the diverse encapsulation of cells of different sizes and quantities. Furthermore, the cost for each microfluidic CFSE chip is approximately USD 3, making it a low-cost approach for 3D cell culture. The proposed device is successfully applied in the 3D culture of saccharomyces cerevisiae cells with an occurrence rate for proliferation of 80.34 ± 3.77%. With low-cost, easy-to-operate, high-throughput, and miniaturization characteristics, the proposed device meets the requirements for 3D in vitro cell culture and is expected to be applied in biological fields such as drug toxicology and pharmacokinetics.

Droplet Microfluidics for High-Throughput Analysis of Antibiotic Susceptibility in Bacterial Cells and Populations

Antibiotic-resistant bacteria are an increasing concern both in everyday life and specialized environments such as healthcare. As the rate of antibiotic-resistant infections rises, so do complications to health and the risk of disability and death. Urgent action is required regarding the discovery of new antibiotics and rapid diagnosis of the resistance profile of an infectious pathogen as well as a better understanding of population and single-cell distribution of the resistance level. High-throughput screening is the major affordance of droplet microfluidics. Droplet screens can be exploited both to look for combinations of drugs that could stop an infection of multidrug-resistant bacteria and to search for the source of resistance via directed-evolution experiments or the analysis of various responses to a drug by genetically identical bacteria. In droplet techniques that have been used in this way for over a decade, aqueous droplets containing antibiotics and bacteria are manipulated both within and outside of the microfluidic devices. The diagnostics problem was approached by producing a series of microfluidic systems with integrated dilution modules for automated preparation of antibiotic concentration gradients, achieving the speed that allowed for high-throughput combinatorial assays. We developed a method for automated emulsification of a series of samples that facilitated measuring the resistance levels of thousands of individual cells encapsulated in droplets and quantifying the inoculum effect, the dependence of resistance level on bacterial cell count. Screening of single cells encapsulated in droplets with varying antibiotic contents has revealed a distribution of resistance levels within populations of clonally identical cells. To be able to screen bacteria from clinical samples, a study of fluorescent dyes in droplets determined that a derivative of a popular viability marker is more suitable for droplet assays. We have developed a detection system that analyzes the growth or death state of bacteria with antibiotics for thousands of droplets per second by measuring the scattering of light hitting the droplets without labeling the cells or droplets. The droplet-based microchemostats enabled long-term evolution of resistance experiments, which will be integrated with high-throughput single-cell assays to better understand the mechanism of resistance acquisition and loss. These techniques underlie automated combinatorial screens of antibiotic resistance in single cells from clinical samples. We hope that this Account will inspire new droplet-based research on the antibiotic susceptibility of bacteria.

Easy-to-Operate Co-flow Step Emulsification Device for Droplet Digital Polymerase Chain Reaction

Digital polymerase chain reaction (PCR) plays important roles in the detection and quantification of nucleic acid targets, while there still remain challenges including high cost, complex operation, and low integration of the instrumental system. Here, in this work, a novel microfluidic chip based on co-flow step emulsification is proposed for droplet digital PCR (ddPCR), which can achieve droplet generation, droplet array self-assembly, PCR amplification, and fluorescence detection on a single device. With the combination of single-layer lithography and punching operation, a step microstructure was constructed and it served as the key element to develop a Laplace pressure gradient at the Rayleigh-Plateau instability interface so as to achieve droplet generation. It is demonstrated that the fabrication of step microstructure is low cost, easy-to-operate, and reliable. In addition, the single droplet volume can be adjusted flexibly due to the co-flow design; thus, the ddPCR chip can get an ultrahigh upper limit of quantification to deal with DNA templates with high concentrations. Furthermore, the volume fraction of the resulting droplets in this ddPCR chip can be up to 72% and it results in closely spaced droplet arrays, makes the best of CCD camera for fluorescence detections, and is beneficial for the minimization of a ddPCR system. The quantitative capability of the ddPCR chip was evaluated by measuring template DNA at concentrations from 20 to 50 000 copies/μL. Owing to the characteristics of low cost, easy operation, excellent quantitative capability, and minimization, the proposed ddPCR chip meets the requirements of DNA molecule quantification and is expected to be applied in the point-of-care testing field.

Micro and nanofluidics for high throughput drug screening

In this book chapter, we elaborate on the state-of-the-art technology developments in high throughput screening, microfluidics and nanofluidics. This book chapter further elaborated on the application of microfluidics and nanofluidics for high throughput drug screening with respect to communicable diseases and non-communicable diseases such as cancer. As a future perspective, there is tremendous potential for microfluidics and nanofluidics to be applied in high throughput drug screening which could be applied for various biotechnology applications such as in cancer precision medicine, point-of-care diagnostics and imaging. With the integration of Fourth industrial revolution (4IR) technologies with micro and nanofluidics technologies, it envisioned that such integration along with digital health would enable next generation technology development in medical field.

A Review of Capillary Pressure Control Valves in Microfluidics

Microfluidics offer microenvironments for reagent delivery, handling, mixing, reaction, and detection, but often demand the affiliated equipment for liquid control for these functions. As a helpful tool, the capillary pressure control valve (CPCV) has become popular to avoid using affiliated equipment. Liquid can be handled in a controlled manner by using the bubble pressure effects. In this paper, we analyze and categorize the CPCVs via three determining parameters: surface tension, contact angle, and microchannel shape. Finally, a few application scenarios and impacts of CPCV are listed, which includes how CPVC simplify automation of microfluidic networks, work with other driving modes; make extensive use of microfluidics by open channel, and sampling and delivery with controlled manners. The authors hope this review will help the development and use of the CPCV in microfluidic fields in both research and industry.

Microfluidic formation of crystal-like structures

Crystal-like structures find application in several fields ranging from biomedical engineering to material science. For instance, droplet crystals are critical for high throughput assays and material synthesis, while particle crystals are important for particles and cell encapsulation, Drop-seq technologies, and single-cell analysis. Formation of crystal-like structures relies entirely on the possibility of manipulating with great accuracy the micrometer-size objects forming the crystal. In this context, microfluidic devices offer versatile tools for the precise manipulation of droplets and particles, thus enabling fabrication of crystal-like structures that form due to hydrodynamic interactions among droplets or particles. In this review, we aim at providing an holistic representation of crystal-like structure formation mediated by hydrodynamic interactions in microfluidic devices. We also discuss the physical origin of these hydrodynamic interactions and their relation to parameters such as device geometry, fluid properties, and flow conditions.

Microdroplet Operations in Polymeric Microtubes

Microsystem technologies allow a plethora of operations to be achieved for microemulsion- and microdroplet-based assays, providing miniaturized, yet large-throughput capabilities to assist experimentation in analytical chemistry, biology, and synthetic biology. Many of such approaches have been implemented on-chip, using microfluidic and lab-on-a-chip technologies. However, the microfabrication of such devices relies on expensive equipment and time-consuming methods, thus hindering their uptake and use by many research laboratories where microfabrication expertise is not available. Here, we demonstrate how fundamental water-in-oil microdroplet operations, such as droplet trapping, merging, diluting, and splitting, can be obtained using straightforward, inexpensive, and manually fabricated polymeric microtube modules. The modules are based on creating an angled tubing interface at the interconnection between two polymeric microtubes. We have characterized how the geometry and fluid dynamic conditions at this interface enabled different droplet operations to be achieved in a versatile and functional manner. We envisage this approach to be an alternative solution to expensive and laborious microfabrication protocols for droplet microfluidic applications.

Study of Active Janus Particles in the Presence of an Engineered Oil-Water Interface

We present a systematic study of motion of Pt@SiO₂ Janus particles at a liquid-liquid interface. A special microfluidic trap is used for creating such an interface. The increased surface energy of the large surface results in partial wetting of the substrate, leaving patches of oil on the glass surface. This allows us to directly compare the motion at the two interfaces, i.e., oil-water and solid-water interface within the same setting, guaranteeing identical conditions in terms of additional parameters. The propulsion behavior of Janus particles is found to be quantitatively similar at both surfaces. The interplay of reaction product absorption by oil, slip locking by surfactant, microscale friction, lubrication efficiency, and potential Marangoni effect controls the resemblance of motion characteristics at the two interfaces. Additionally, we also observed guidance effect on the Janus particles by the pinning line of oil patches, similar to solid side walls.

Buoyancy-driven step emulsification on pneumatic centrifugal microfluidic platforms

We present here a new method for controlling the droplet size in step emulsification processes on a centrifugal microfluidic platform, which, in addition to the centrifugal force, uses pneumatic actuation for fluid displacement. We highlight the importance of the interplay between buoyancy effects and the flow rate at the step junction, and provide a simple analytical model relating these two quantities to the size of the droplets. Numerical models as well as experiments with water-in-oil emulsions are performed in support of the proposed model.

Microfluidic Chamber Design for Controlled Droplet Expansion and Coalescence

The defined formation and expansion of droplets are essential operations for droplet-based screening assays. The volumetric expansion of droplets causes a dilution of the ingredients. Dilution is required for the generation of concentration graduation which is mandatory for many different assay protocols. Here, we describe the design of a microfluidic operation unit based on a bypassed chamber and its operation modes. The different operation modes enable the defined formation of sub-µL droplets on the one hand and the expansion of low nL to sub-µL droplets by controlled coalescence on the other. In this way the chamber acts as fluidic interface between two fluidic network parts dimensioned for different droplet volumes. Hence, channel confined droplets of about 30–40 nL from the first network part were expanded to cannel confined droplets of about 500 to about 2500 nL in the second network part. Four different operation modes were realized: (a) flow rate independent droplet formation in a self-controlled way caused by the bypassed chamber design, (b) single droplet expansion mode, (c) multiple droplet expansion mode, and (d) multiple droplet coalescence mode. The last mode was used for the automated coalescence of 12 droplets of about 40 nL volume to produce a highly ordered output sequence with individual droplet volumes of about 500 nL volume. The experimental investigation confirmed a high tolerance of the developed chamber against the variation of key parameters of the dispersed-phase like salt content, pH value and fluid viscosity. The presented fluidic chamber provides a solution for the problem of bridging different droplet volumes in a fluidic network.

Gravity-driven microfluidic assay for digital enumeration of bacteria and for antibiotic susceptibility testing

The alarming dynamics of antibiotic-resistant infections calls for the development of rapid and point-of-care (POC) antibiotic susceptibility testing (AST) methods. Here, we demonstrated the first completely stand-alone microfluidic system that allowed the execution of digital enumeration of bacteria and digital antibiograms without any specialized microfluidic instrumentation. A four-chamber gravity-driven step emulsification device generated ∼2000 monodisperse 2 nanoliter droplets with a coefficient of variation of 8.9% of volumes for 95% of droplets within less than 10 minutes. The manual workload required for droplet generation was limited to the sample preparation, the deposition into the sample inlet of the chip and subsequent orientation of the chip vertically without an additional pumping system. The use of shallow chambers imposing a 2D droplet arrangement provided superior stability of the droplets against coalescence and minimized the leakage of the reporter viability dye between adjacent droplets during long-term culture. By using resazurin as an indicator of the growth of bacteria, we were also able to reduce the assay time to ∼5 hours compared to 20 hours using the standard culture-based test.

Split or slip – passive generation of monodisperse double emulsions with cores of varying viscosity in microfluidic tandem step emulsification system

We investigate the role of viscosities on the formation of double emulsion in a microfluidic step emulsification system. Aqueous droplets of various viscosities and sizes were engulfed in fluorocarbon oil and subsequently transformed into double droplets in the microfluidic step emulsifying device. We identify two distinct regimes of double droplet formation: (i) core droplets split into multiple smaller droplets, or (ii) cores slip whole into the forming oil shell. We show that the viscosity ratio of the core and shell phases plays a crucial role in determining the mode of formation of the double emulsions. Finally, we demonstrate that high viscosity of the core droplet allows for generation of double emulsions with constant shell thickness for cores of various sizes.

We investigate the role of fluid viscosities on formation of double emulsion in a microfluidic step emulsification system. The ratio of fluid viscosities controls double droplet formation, leading to splitting of the core for low core-to-shell viscosity ratio.

[Application of femtosecond laser technology in the management of subluxated lens]

OBJECTIVE

To evaluate the application of femtosecond laser technology in the management of subluxated lens.

METHODS

We retrospectively analyzed the data of the patients with subluxated lens undergoing femtosecond laser- assisted surgery at the Cataract Center of Guangzhou Aier Eye Hospital between March, 2017 and May, 2019. The LenSx femtosecond laser-assisted cataract surgery system was used to perform capsulotomy and lens fragmentation. According to the patients' eye condition, anterior vitrectomy was performed and capsular retractors was used. After phacoemulsification, I/A and insertion of the tension rings, the intraocular lens (IOL) was implanted into the capsular bag. The perioperative data, complications, visual acuity and intraocular pressure after the operation were recorded, and the stability of the capsular bag and IOLs were assessed.

RESULTS

We analyzed the data of 25 cases (29 eyes) of subluxated lens, including 16 (16 eyes; 55.17%) as the result of traumatic lens subluxation, 5 (9 eyes; 31.03%) of Mafan syndromes, 1 case (1 eye; 3.45%) of high myopia and 3 cases (3 eyes; 10.34%) of unknown causes. Thirteen 13 eyes (44.83%) showed mild subluxation, 7 (24.14%) had moderate subluxation, and 9 (31.03%) had severe subluxation. Femtosecond laser- assisted capsulorhexis, lens fragmentation and phacoemulsification were successfully completed for 29 eyes, of which 28 eyes (96.55%) retained the complete capsular bag and with successful implantation of the capsular tension devices and IOLs. Nine eyes (31.03%) were treated with anterior segment vitrectomy; iris hooks were used for 2 eyes (6.90%) and capsular bag hooks for 9 eyes (31.03%). The best corrected visual acuity was significantly improved in 29 eyes after operation (P < 0.05). At 1 month after the surgery, 26 eyes (89.66%) showed stably centered IOLs, 2 eyes (6.90%) showed slight tilt of the IOLs, and 3 eyes (10.34%) had anterior capsular contraction. The intraoperative complications included subconjunctival hemorrhage (75.87%), incomplete capsulotomy (17.24%) and contracted pupils (13.79%).

CONCLUSIONS

The application of femtosecond laser assisted technology enhances the surgical safety and effectiveness for subluxated lens, facilitates the choice of individualized surgical options, and promotes maximum recovery of the patients' visual function.

Monodisperse droplet formation by spontaneous and interaction based mechanisms in partitioned EDGE microfluidic device

The partitioned EDGE droplet generation device is known for its’ high monodisperse droplet formation frequencies in two distinct pressure ranges, and an interesting candidate for scale up of microfluidic emulsification devices. In the current study, we test various continuous and dispersed phase properties and device geometries to unravel how the device spontaneously forms small monodisperse droplets (6–18 μm) at low pressures, and larger monodisperse droplets (>28 μm) at elevated pressures. For the small droplets, we show that the continuous phase inflow in the droplet formation unit largely determines droplet formation behaviour and the resulting droplet size and blow-up pressure. This effect was not considered as a factor of significance for spontaneous droplet formation devices that are mostly characterised by capillary numbers in literature. We then show for the first time that the formation of larger droplets is caused by physical interaction between neighbouring droplets, and highly dependent on device geometry. The insights obtained here are an essential step toward industrial emulsification based on microfluidic devices.

Microfluidic screening of antibiotic susceptibility at a single-cell level shows the inoculum effect of cefotaxime on E. coli

Measurement of antibiotic susceptibility at the level of single cells is important as it reveals the concentration of an antibiotic that leads to drug resistance in bacterial strains. To date, no solution for large-scale studies of antibiotic susceptibility at the single-cell level has been shown. Here, we present a method for production and separation of emulsions consisting of subnanoliter droplets that allows us to identify each emulsion by their spatial position in the train of emulsions without chemical barcoding. The emulsions of droplets are separated by a third immiscible phase, thus forming large compartments-tankers-each filled with an emulsion of droplet reactors. Each tanker in a train can be set under different reaction conditions for hundreds or thousands of replications of the same reaction. The tankers allow for long term incubation - needed to check for growth of bacteria under a screen of conditions. We use microfluidic tankers to analyze susceptibility to cefotaxime in ca. 1900 replications for each concentration of the antibiotic in one experiment. We test cefotaxime susceptibility for different initial concentrations of bacteria, showing the inoculum effect down to the level of single cells for more than a hundred single-cell events per tanker. Lastly, we use tankers to observe the formation of aggregates of bacteria in the presence of cefotaxime in the increasing concentration of the antibiotic. The microfluidic tankers allow for facile studies of the inoculum effect and antibiotic susceptibility, and constitute an attractive, label-free screening method for a variety of other experiments in chemistry and biology.

Droplet microfluidics for high-sensitivity and high-throughput detection and screening of disease biomarkers

Biomarkers are nucleic acids, proteins, single cells, or small molecules in human tissues or biological fluids whose reliable detection can be used to confirm or predict disease and disease states. Sensitive detection of biomarkers is therefore critical in a variety of applications including disease diagnostics, therapeutics, and drug screening. Unfortunately for many diseases, low abundance of biomarkers in human samples and low sample volumes render standard benchtop platforms like 96-well plates ineffective for reliable detection and screening. Discretization of bulk samples into a large number of small volumes (fL-nL) via droplet microfluidic technology offers a promising solution for high-sensitivity and high-throughput detection and screening of biomarkers. Several microfluidic strategies exist for high-throughput biomarker digitization into droplets, and these strategies have been utilized by numerous droplet platforms for nucleic acid, protein, and single-cell detection and screening. While the potential of droplet-based platforms has led to burgeoning interest in droplets, seamless integration of sample preparation technologies and automation of platforms from biological sample to answer remain critical components that can render these platforms useful in the clinical setting in the near future. This article is categorized under: Diagnostic Tools > Biosensing Diagnostic Tools > Diagnostic Nanodevices Therapeutic Approaches and Drug Discovery > Emerging Technologies Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease.

A precise and accurate microfluidic droplet dilutor

We demonstrate a microfluidic system for the precise (coefficient of variance between repetitions below 4%) and highly accurate (average difference from two-fold dilution below 1%) serial dilution of solutions inside droplets with a volume of ca. 1 μl. The two-fold dilution series can be prepared with the correlation coefficient as high as R² = 0.999. The technique that we here describe uses hydrodynamic traps to precisely meter every droplet used in subsequent dilutions. We use only one metering trap to meter each and every droplet involved in the process of preparation of the dilution series. This eliminates the error of metering that would arise from the finite fidelity of fabrication of multiple metering traps. Metering every droplet at the same trap provides for high reproducibility of the volumes of the droplets, and thus high reproducibility of dilutions. We also present a device and method to precisely and accurately dilute one substance and simultaneously maintain the concentration of another substance throughout the dilution series without mixing their stock solutions. We compare the here-described precise and accurate dilution systems with a simple microdroplet dilutor that comprises several traps - each trap for a subsequent dilution. We describe the effect of producing more reproducible dilutions in a simple microdroplet dilutor thanks to the application of an alternating electric field.

Emulsion templated vesicles with symmetric or asymmetric membranes

Emulsion droplets with well-controlled topologies are used as templates for forming vesicles with either symmetric or asymmetric membranes. This review summarizes the available technology to produce these templates, the strategies and critical parameters involved in the transformation of emulsion droplets into vesicles, and the properties of the generated vesicles, with a special focus on the composition and material distribution of the vesicle membrane. Here, we also address limitations in the field and point to future fundamental and applied research in the area.

Controlled droplet microfluidic systems for multistep chemical and biological assays

Droplet microfluidics is a relatively new and rapidly evolving field of science focused on studying the hydrodynamics and properties of biphasic flows at the microscale, and on the development of systems for practical applications in chemistry, biology and materials science.