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Microfluidic droplet technique is a new technology developed on the basis of microfluidics to study the formation, manipulation and application of microdroplets of a few micrometers size. It drastically enhances the advantages of microfluidics in terms of low consumption, automation and high throughput and is widely used in chemical, microelectronics, materials science, biology and biomedical engineering etc. In this paper, an iterative learning control (ILC) scheme is proposed to accurately control the droplet size at low capillary numbers. ILC is able to revise the current control input based on the error information measured during previous experimental operations and ultimately produce the desired droplet size in the T-junction microfluidic channel we design. The feasibility of the ILC scheme is verified through experiments, where two different situations are addressed in detail. The results indicate that only a few number of iterations is required to achieve the desired droplet size. The main characteristics of the proposed ILC scheme are as follow: (1) it does not require an accurate mathematical model of the microfluidic systems, which can resolve the severe uncertainties of complex droplet microfluidic system well. (2) Owing to the feedforward characteristic and simple structure of ILC, it is easier to be implemented in practical experimental environments than typical feedback controllers, e.g., proportional-integral-derivative controller. (3) Compared with the traversal methods widely used in medical and biological fields, the idea of ILC would reduce the number of experimental trials significantly.

In Y-shaped microfluidic chip, the laminar flow refers to a phenomenon that two fluids introduced from two inlets flow side by side without turbulence and form two stable streams in outlet with a common interface. The interface position of laminar flow has significant influence in some experiment analysis of life science, such as molecule diffusion and solvent extraction, where there are still a series of problems associated with the manipulation of interface position. In this brief, an iterative learning control (ILC) scheme is proposed for precise control of the laminar flow position. ILC can improve the current input signal iteratively based on the experimental results achieved in the previous trials and eventually produce the desired interface position in output channel. To verify the effectiveness of the proposed ILC scheme, we design and fabricate the Y-shaped microfluidic chips. Furthermore, two different scenarios are considered, where the results show that an appropriate input signal achieving the desired output can be promptly obtained via ILC. The three main advantages of the proposed control scheme lie in: 1) the simple structure and the feedforward characteristic of the control scheme make it implementable in an easy way; 2) it is a partially model-free method, and hence, no accurate model of laminar flow is required and system uncertainties can be dealt with rigorously when designing the controller; and 3) compared with the well-adopted traversal methods in life science research, the idea of ILC reduces the number of experimental trials remarkably.

A novel strategy was proposed for preparing micro-scale monodisperses nitrifying bacteria (NB) encapsulated Ca-Alg@CaCO3 colloidosomes by exploiting capillary microfluidic device, as an attempt to treat ammonium-nitrogen wastewater in an environment-friendly, efficient and repeatable manner based on the aqueous two-phase (ATPS) system. By complying with the spatial confined urease mediate biomineralization reactions, ATPS droplets (Dextran in Polyethylene glycol) containing urease, NB regent and alginate were used as templates to prepare 500 μm Ca-Alg@CaCO3 colloidosomes with 16.48 Mpa mechanical strength. The activity of NB encapsulated in the colloidosomes was high. The simulated wastewater treated with the colloidosomes achieved a high removal rate even at harsh temperature and pH value. In both simulated and real wastewater treatment, prolonged reuse times (216 h) with high removal rate (＞90%, after being applied 72 h) were obtained by using Ca-Alg@CaCO3 colloidosomes, as compared with that (96 h) by using general alginate microbeads.

A robust Pickering emulsion stabilized by lipase-immobilized alginate gel microparticles with a coating of silanized titania nanoparticles is developed for biphasic biocatalysis. The good recyclability and high stability of the proposed interfacial catalysis system have been verified, retaining about 90% of relative enzyme activity in 10 catalytic cycles with operation for 240 h. Meanwhile the Pickering emulsions remain stable during a storage time of one year. The green system can be widely applied to construct powerful platforms for enzyme or microorganism-driven interfacial catalysis.

Chaining configurations (e.g. 2-chain) have been widely applied in service systems to improve responsiveness to customer demand. In this paper, we propose an approximation method for the analysis o...

A facile method was developed to produce porous alginate beads (PABs) with a controllable interconnected porous structure with aqueous two phase (ATPS) emulsions as template for 3D cell culture. ATPS emulsions, containing two biocompatible immiscible aqueous phases of cell/dextran (Dex) mixture and alginate (Alg)/polyethylene glycol (PEG) mixture and stabilized by mPEG-BSA particles, were introduced to form PABs. The pore size of PABs could be controlled by changing the emulsification frequency and the volume ratio between the ATPS emulsions and PEG-Alg solution. Moreover, cells could be directly encapsulated in the interconnected pores due to the excellent biocompatibility of ATPS. HeLa and human liver cancer cells encapsulated in the PABs present stronger cell activity (>95 %), proliferation, and enhanced functions compared with the cells encapsulated in general alginate beads (GABs). It is believed that the PABs is a promising microcarriers for 3D cell culture in vitro.

Background: Randomized controlled trials have confirmed the safety of a restrictive red-cell tranfusion threshold (8 g/dL) versus a liberal threshold in cardiac and orthopedic surgeries. We aim to examine whether these findings can be replicated with observational data and generalized to broader specialties and a lower threshold. Methods: This is a prospective observational study conducted in three region-representative hospitals in China. Inpatients aged ≥18 years undergoing surgeries from six red cell-consumptive specialties (2015–2016) were defined as the base population. Three criteria were used to derive an analytic population: no significant intraoperative bleeding (

Although there are several reports showing the employment of aqueous two-phase systems (ATPS) for biotransformation in large-scale, the industrial application of ATPS is still hampered by their drawbacks such as slow diffusive mass transfer, long settling time for phase separation, and batch processes. Here, we propose for the first time a continuous-flow process based on a suitably designed ATPS parallel-laminar flow in a double Y-branched microfluidic device using for enzymatic catalysis. In a model urease reaction, polyethylene glycol (PEG) 8 kDa and dextran (Dex) 500 kDa are selected as polymer solutions, in which the enzymes settle mainly in the Dex phase while the products partition mainly to the PEG phase during short residence time. On account of rapid micro-transport, as well as integrate one single step of biocatalysis and separation process, obvious intensification of enzymatic catalysis in such ATPS microfluidic platform is demonstrated. Compared with the conventional ATPS in a beaker under gentle stirring, the enzymatic reaction rate in ATPS microfluidic is 500 times higher. Furthermore, the effects of flow rates, substrate concentration, residence time, and recycling number on the reaction rate and conversion rate are evaluated, respectively. Our study provides an all-aqueous, micro-scale and coupled reaction-separation platform for the process intensification of enzymatic catalysis, which has not only theoretical significance, but also practical value for biotransformation-based fields, such as biomedical, pharmaceuticals and food applications.

Water-in-water (w/w) emulsions are attractive microcompartmentalized platforms due to their outstanding biocompatibility. To address the main disadvantage of poor stability that hampers their practical application, here we report a novel type of polymer-protein conjugate emulsifier obtained by Schiff base synthesis to stabilize w/w emulsions. In particular, the proposed mild approach benefits the modification of proteins of suitable size and wettability as particulate emulsifiers retaining their bioactivity. As demonstrated in a model system, the methoxy polyethylene glycol (mPEG)-urease conjugate particles anchor at the w/w interfaces, where they serve as an effective emulsifier-combined-catalyst and catalyze the hydrolysis of urea in water to ammonium carbonate. Our study is unique in that it employs bioactive particles to stabilize w/w emulsions. Considering the characteristics of all-aqueous, compartmental and interfacial biocatalysis of the system, it will open up new possibilities in the life sciences.

A simple process is developed for the one-step preparation of dual-compartment alginate microcapsules with controlled size and structure from microfluid-generated water-in-water-in-oil (W/W/O) emulsion droplet. Unlike other methods that rely on transient W/W/O emulsion droplet, we introduce an aqueous two-phase system (ATPS) to form a stable W/W/O emulsion droplet as a template for preparing dual-compartment alginate microcapsules. Two different bioactive molecules are able to be spatially confined encapsulated in the shell and core of alginate microcapsules due to the partitioning effect of ATPS and the high viscosity of alginate solution. Moreover, an enzyme cascade reaction with a spatial confined glucose oxidase and horseradish peroxidase in the shell and core of alginate microcapsules confirms its excellent biocompatibility and high activity. This method provides a green platform for enzyme-catalyzed tandem reactions and controlled sequential release of multiple drugs based on alginate microcapsules.

A facile and green approach is developed for fabricating colloidosomes with well-controlled size and structure from the microfluidic-generated aqueous two-phase system (ATPS) emulsion droplet. Unlike other methods that rely on self-assembly of externally added colloidal particles at the emulsion interface, urease-mediated biomineralization induced by "drainage" is introduced to form CaCO3 particles at the alginate emulsion interface for preparing Ca-alg@CaCO3 colloidosomes. Two types of bioactive molecules (bovine serum albumin and catalase) can be encapsulated with high efficiency (>85%) because of the partitioning effect of the ATPS and high viscosity of alginate solution. The encapsulated bioactive molecules can be controllably released by regulating the compactness of colloidosomes. Moreover, after being freeze-dried or dried at 37 °C, the activity of catalase in colloidosomes is obviously higher than that in alginate hydrogels, which confirms that the Ca-alg@CaCO3 structure has strong protection for inclusions. We believe that the biocompatible and controllable Ca-alg@CaCO3 colloidosomes possess great potential applications in bioencapsulation for foods, daily chemicals, and synthetic protocell formation.

This is the peer reviewed version of the following article: Cao, P., Wang, Y. and Xie, J. (2019), Priority Service Pricing with Heterogeneous Customers: Impact of Delay Cost Distribution. Prod Oper Manag, 28: 2854-2876., which has been published in final form at https://doi.org/10.1111/poms.13086. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. National Natural Science Foundation of China

ObjectivesTo develop a risk-stratified intervention strategy and evaluate its effect on reducing surgical complications.DesignA multicentre prospective study with preintervention and postintervention stages: period I (January to June 2015) to develop the intervention strategy and period II (January to June 2016) to evaluate its effectiveness.SettingFour academic/teaching hospitals representing major Chinese administrative and economic regions.ParticipantsAll surgical (elective and emergent) inpatients aged ≥14 years with a minimum hospital stay of 24 hours, who underwent a surgical procedure requiring an anesthesiologist.InterventionsTargeted complications were grouped into three categories (common, specific, serious) according to their incidence pattern, severity and preventability. The corresponding expert consensus-generated interventions, which focused on both regulating medical practices and managing inherent patient-related risks, were implemented in a patient-tailored way via an electronic checklist system.Primary and secondary outcomesPrimary outcomes were (1) in-hospital death/confirmed death within 30 days after discharge and (2) complications during hospitalisation. Secondary outcome was length of stay (LOS).ResultsWe included 51 030 patients in this analysis (eligibility rate 87.7%): 23 413 during period I, 27 617 during period II. Patients’ characteristics were comparable during the two periods. After adjustment, the mean number of overall complications per 100 patients decreased from 8.84 to 7.56 (relative change 14.5%; PConclusionsImplementing a risk-stratified intervention strategy may be a target-sensitive, convenient means to improve surgical outcomes.

BACKGROUND AND OBJECTIVES A health industry standard recommending restrictive transfusion is to be in effect in China in April 2019. We aim to explore its potential economic and clinical impacts among surgical patients. MATERIALS AND METHODS A decision tree model was applied to compare cost-effectiveness of current routine transfusion in China, a restrictive (transfusion at Hb

Large-scale single-cell arrays are urgently required for current high-throughput screening of cell function and heterogeneity. However, the rapid and convenient generation of large-scale single-cell array in a multiplex and universal manner is not yet well established. In this paper, we report a simple and reliable method for the generation of a single-cell array by combining pneumatic microvalve arrays (PμVAs) and hydrodynamic single-cell trapping sites in a single microfluidic device. The PμVAs, which can be precisely controlled by actuated pressures, were designed to guide multiple types of cells being trapped in the corresponding single-cell trapping sites located in the fluidic channel. According to the theoretical demonstration and computational simulation, we successfully realized a multiplex single-cell array with three different types of cells by a step-by-step protocol. Furthermore, the analysis of cellular esterase heterogeneity of the three types of cells was concurrently implemented in the device as a proof-of-concept experiment. All the results demonstrated that the method developed in the current study could be applied for the generation of large-scale single-cell array with multiple cell types, which would be also promising and helpful for single-cell-based high-throughput drug test, multipurpose immunosensor and clinical diagnosis.

Emulsion droplets can serve as ideal compartments for reactions. In fact, in many cases, the chemical reactions are supposed to be triggered at a desired position and time without change of the system environment. Here, we present a type of light and magnetic dual-responsive Pickering emulsion microreactor by coadsorption of light-sensitive titania (TiO2) and super paramagnetic iron oxide (Fe3O4) nanoparticles at the oil-water interface of emulsion droplets. The droplets encapsulating different reactants in advance can be driven close to each other by an external magnetic field, and then the chemical reaction is triggered by UV illumination due to the contact of the isolated reactants as a result of droplet coalescence. An insight into the incorporation of hydrophobic TiO2 and hydrophilic Fe3O4 nanoparticles simultaneously at the emulsion interface is achieved. On the basis of that, an account is given of the coalescence mechanism of the Pickering emulsion microreactors. Our work not only provides a novel Pickering emulsion microreactor platform for triggering chemical reactions in a nonintrusive and well-controlled way but also opens a promising avenue to construct multifunctional Pickering emulsions by assembly of versatile building block nanoparticles at the interface of emulsion droplets.

Micropatterning technologies are emerging as an enabling tool for various microfluidic-based applications in life sciences. However, the high throughput and multiplex localization of multiple bio-components in a microfluidic device has not yet been well established. In this paper, we describe a simple and in situ micropatterning method using an integrated microfluidic device with pneumatic microstructures (PμSs) for highly controllable immobilization of both proteins and cells in a high throughput, geometry-dynamic, and multi-patterning way. The precise Pluronic F127 passivation of a microchamber surface except the PμS-blocked regions was performed and characterized, and the spatial dynamics and consistency of both the PμSs and protein/cell micropatterning were optically evaluated and quantitatively demonstrated too. Furthermore, a systematic investigation of PμS-assisted micropatterning in microfluidics was carried out. The feature of high throughput and spatial control of micropatterning can be simply realized by using the well-designed PμS arrays. Meanwhile, the co-micropatterning of different proteins (bovine serum albumin and chicken egg albumin) and cells (human umbilical vein endothelial cells and human hepatocellular carcinoma cells) in a microfluidic device was successfully accomplished with the orderly serial manipulation of PμS groups. We demonstrate that PμS-assisted micropatterning can be applied as a convenient microfluidic component for large-scale and diversified protein/cell patterning and manipulation, which could be useful for cell-based tissue organization, high-throughput imaging, protein-related interactions and immunoassays.

Soil nematode communities can provide important information about soil food web structure and function. However, how soil nematode communities and their metabolic footprints change over time in temperate forests is not well known. We examined the changes in the composition, diversity and metabolic footprints of soil nematode communities in three differently-aged (young, mid and old) forests of the Changbai Mountains, China. Carbon flows through different nematode trophic groups were also quantified based on nematode biomasses. The results showed that the highest abundance and diversity of total nematodes was found in the mid forest. Nematode communities were characterized by the replenishment in abundance but not the replacement of dominant genera. A low enrichment footprint in the young forest suggests a decline in available prey, while a high enrichment footprint in the mid forest indicates an increase in resource entry into soil food web. The relationship between the carbon flows of omnivores-predators and fungivores was stronger than that among other trophic groups. Our study shows that bottom-up effects of the vegetation, the soil environment and the connectedness of nematode trophic groups are all important driving forces for nematode community structure in temperate forests.

Development of a robust method for the preparation of cell aggregates with different shapes is one of the urgent requirements in tissue engineering, since they can be used as building blocks to mimic complex architectures in tissues. Herein, we describe a microfluidic droplet-based approach that can easily produce different shapes of cell aggregates in Ca-alginate microparticles by changing alginate and CaCl2 concentrations. Using this approach, human cervical carcinoma, human hepatocellular liver carcinoma and human umbilical vein endothelial cell aggregates with spherical, spindle- and branch-like shapes were successfully obtained in a repeatable and controllable manner. Cytoskeletal analysis and SEM observation showed that the cell aggregates were densely packed and interconnected. Cell viability assays showed that the viabilities of the retrieved cells from the Ca-alginate microparticles were all more than 95% with good morphology and proliferation ability. Study on the formation mechanism revealed that the shape and size of the cell aggregates were mainly decided by the inner structures of Ca-alginate microparticles, which can be controlled by regulating their preparation conditions. This approach may possess great potential for the construction of various building blocks in tissue engineering with simplicity, controllability, applicability and practicality.

The development of a novel and simple method to trace lead ions (Pb2+) has received great attention due to its high toxicity to human health and the environment. In this paper, we describe a new polydiacetylene (PDA)-based liposome sensor for the colorimetric and fluorometric detection of Pb2+ in aqueous solution and in alginate hydrogel microbeads. In the sensor system, a dopamine group was rationally introduced into a diacetylene monomer to work as a strong binding site for Pb2+. The dopamine-functionalized monomer and 10,12-pentacosadiynoic acid (PCDA) were then incorporated into PDA liposomes in aqueous solution. After UV light-induced polymerization, deep blue colored liposome solutions were obtained. Upon the addition of various metal ions into the liposome solution, only Pb2+ could cause a distinct color change from blue to red and a dramatic fluorescence enhancement. To further improve its sensitivity and address its intrinsic aggregation, we then developed a liposome-immobilized detection system by encapsulating PDA–DA liposomes into alginate hydrogel beads through a microfluidic droplet-based method. The results showed that the PDA–DA liposome-containing hybrid hydrogel beads possessed excellent stability and high sensitivity. These interesting findings demonstrated that the PDA liposome system developed in the current study may offer a new method for Pb2+ recognition in a more efficient manner.

This paper studies the priority pricing problem for a single-server queueing system with two priority classes in which customers have different sensitivities to delay. The system makes a fixed-delay announcement to inform arriving customers of the expected delay for each class, whereupon each customer must decide which class to join. Any customer who joins the priority class is charged a fixed priority price. Our examination of customers' joining behavior under any given priority prices reveals that there can be multiple equilibrium delays and that the number of those delays depends on the structure of customers' delay cost distribution. We characterize the stability of these equilibria and show that the system can reach the largest or smallest equilibrium by making a proper initial delay announcement. In addition, we consider two pricing problems to maximize the system's long-run average revenue and social welfare respectively. The results derived here establish that both the revenue-maximizing price and the social welfare--maximizing price are quite sensitive to the delay cost distribution. Finally, we investigate the influence of the number of priority classes by extending the two--priority-class model to a multiple--priority-class model.

A pneumatic microchannel network (PμCN) fabrication method for producing a three-dimensional microvascular system in an integrated microfluidic device is described. The spatial dynamics of the PμCN profile is systematically characterized and quantitatively analyzed. A microvessel network-embedded hydrogel scaffold is constructed using in situ pneumatic actuation of the PμCN and collagen polymerization. The endothelium-containing microvasculature, which has high cell viability and typical vascular features, was formed by seeding and cultivating human umbilical vein endothelial cells (HUVEC-C). Furthermore, a quantitative investigation of the adhesive interactions between breast cancer cells and endothelial cells was performed with vascular tissue-mimicry in the hydrogel-supported endothelial network using human breast cancer cells (MDA-MB-231) and HUVEC-C cells. The results show signal-promoted and region-preferred adhesion of cancer cells in the established microvascular network. The PμCN can be applied as an active microfluidic molding component for convenient and robust reproduction of microvasculature in vitro. PμCN application can be valuable in monitoring and investigating blood vessel-involved physiologic/pathologic processes. Moreover, this method will facilitate controllable parenchymal tissue organization and construction for tissue engineering as well as subsequent applications for clinical medicine.

Recent microfluidic advancements in oxygen gradients have greatly promoted controllable oxygen-sensitive cellular investigations at microscale resolution. However, multi-gradient integration in a single microfluidic device for tissue-mimicking cell investigation is not yet well established. In this study, we describe a method that can generate oxygen and chemical concentration gradients in a single microfluidic device via the formation of an oxygen gradient in a chamber and a chemical concentration gradient between adjacent chambers. The oxygen gradient dynamics were systematically investigated, and were quantitatively controlled using simple exchange between the aerial oxygen and the oxygen-free conditions in the gas-permeable polydimethylsiloxane channel. Meanwhile, the chemical gradient dynamics was generated using a special channel-branched device. For potential medical applications of the established oxygen and chemical concentration gradients, a tumor cell therapy assessment was performed using two antitumor drugs (tirapazamine and bleomycin) and two tumor cell lines (human lung adenocarcinoma A549 cells and human cervical carcinoma HeLa cells). The results of the proof-of-concept experiment indicate the dose-dependent antitumor effect of the drugs and hypoxia-induced cytotoxicity of tirapazamine. We demonstrate that the integration of oxygen and chemical concentration gradients in a single device can be applied to investigating oxygen- and chemical-sensitive cell events, which can also be valuable in the development of multi-gradient generating procedures and specific drug screening.

The methodical development of cell biology has resulted in significant advancements in the study of breast tumors. However, the dynamic investigation of the self-seeding process remains largely out of reach. In the present study, we describe a microvalve and liquid membrane double-controlled integrated microfluidic device that provides for the versatile assessment of breast tumor cell invasion dynamics. The liquid membrane formation was first optimized to obtain a high level of control, and was then applied to different types of homotypic and heterotypic cell seeding with precise selective positioning for monoculture and coculture. Using this device, the interaction between breast cancer cells MDA231-LM2 and MDA-MB231 was successfully observed to investigate self-seeding dynamics, including migration, infiltration, and coexistence. The results quantitatively demonstrate the mutual signal-induced attraction between MDA-MB231 and MDA231-LM2 cells, as well as the progressive infiltration of MDA231-LM2 cells into the MDA-MB231 cell population. These results are valuable in the development of spatiotemporal-controlled microfluidic systems and to many microscale-based biological and diagnostic studies involving cell growth, cell differentiation, cell interaction, and cell signal.

The present study presents a new microfluidic device integrated with pneumatic microvalves and a membrane mixer for enzyme-based immunoassay of acute myocardial infarction (AMI) biomarkers, namely, myoglobin, and heart-type fatty acid binding protein (H-FABP). Superparamagnetic microspheres with carboxyl groups on their surfaces were used as antibody solid carriers. A membrane mixer consisting of four ψ-type membrane valves was assembled under the reaction chamber for on-chip performing microsphere trapping and reagent mixing. The entire immunoassay process, including microsphere capture, reagent input, mixing, and subsequent reaction, was accomplished on the device either automatically or manually. The post-reaction substrate resultant was analyzed using a microplate reader. The results show that the average absorbance value is correlated with the concentration of cardiac markers, in agreement with the results obtained using a conventional microsphere-based immunoassay; this indicated that the proposed on-chip immunoassay protocol could be used to detect both myoglobin and H-FABP. The minimum detectable concentration is 5 ng/mL for myoglobin and 1 ng/mL for H-FABP.

This work describes chemical heat shock transformation of foreign plasmid DNA into bacterial host Escherichia coli cells using a capillary-composited microfluidic device. Transformation processes of the loading, mixing, heat shock and recovery of the transformation mixture were carried out automatically in a linear fashion. In addition, by utilizing the capillary with a hollow cylindrical chamber as heating source, simple, low cost local heat shock with accurate heat shock time to transformation mixture was obtained on the microdevice. Results demonstrated that plasmid DNA could be effectively transformed into E. coli, and the transformation efficiency and frequency were as the same level or better than conventional tube-based method. This work complements other microfluidic technologies for potential gene cloning and functional genomics studies.

The presence and quantity of rare cells in the bloodstream of cancer patients provide a potentially accessible source for the early detection of invasive cancer and for monitoring the treatment of advanced diseases. The separation of rare cells from peripheral blood, as a "virtual and real-time liquid biopsy", is expected to replace conventional tissue biopsies of metastatic tumors for therapy guidance. However, technical obstacles, similar to looking for a needle in a haystack, have hindered the broad clinical utility of this method. In this study, we developed a multistage microfluidic device for continuous label-free separation and enrichment of rare cells from blood samples based on cell size and deformability. We successfully separated tumor cells (MCF-7 and HeLa cells) and leukemic (K562) cells spiked in diluted whole blood using a unique complementary combination of inertial microfluidics and steric hindrance in a microfluidic system. The processing parameters of the inertial focusing and steric hindrance regions were optimized to achieve high-throughput and high-efficiency separation, significant advantages compared with existing rare cell isolation technologies. The results from experiments with rare cells spiked in 1% hematocrit blood indicated90% cell recovery at a throughput of 2.24 × 10(7) cells min(-1). The enrichment of rare cells was2.02 × 10(5)-fold. Thus, this microfluidic system driven by purely hydrodynamic forces has practical potential to be applied either alone or as a sample preparation platform for fundamental studies and clinical applications.

Three-dimensional multicellular tumor spheroids have become critical for anticancer study since they may provide a better model than conventional monolayer cultures of cancer cells. Various methods for tumor spheroid formation have been explored. However, only one kind of hydrogel was used in these methods, which has an influence on the size and morphology of the obtained tumor spheroids. Herein, we present a microfluidic droplet-based method for the formation of multicellular tumor spheroids using alginate and matrigel mixed hydrogel beads. By on-chip changing the flow rate of the two hydrogel solutions, mixed hydrogel beads with different volume ratios between alginate and matrigel are obtained. Meanwhile, human cervical carcinoma (HeLa) cells are encapsulated in the mixed hydrogel beads. Acridine orange and propidium iodide double-staining assay shows that the viability of cells encapsulated in the mixed hydrogel beads was more than 90%. After 4 day culture, the multicellular tumor spheroids were successfully formed with spherical shape and uniform size distribution compared with spheroids formed in pure alginate beads. Cytoskeletal analysis by TRITC-phalloidin staining show that HeLa cells in the mixed hydrogel beads closely link to each other. The dose-dependent response assay of HeLa cell spheroids to vincristine show that multicellular spheroids have more powerful resistance to vincristine compared to conventional monolayer culture cells. Taken together, this novel technology may be of importance to facilitate in vitro culture of tumor spheroids for their ever-increasing utilization in modern cell-based medicine.

Myocardial infarction is a major cause of morbidity and mortality worldwide. However, the methodological development of a spatiotemporally controllable investigation of the damage events in myocardial infarction remains challengeable. In the present study, we describe a micropillar array-aided tissue interface mimicking microfluidic device for the dynamic study of hypoxia-induced myocardial injury in a microenvironment-controllable manner. The mass distribution in the device was visually characterized, calculated, and systematically evaluated using the micropillar-assisted biomimetic interface, physiologically relevant flows, and multitype transportation. The fluidic microenvironment in the specifically functional chamber for cell positioning and analysis was successfully constructed with high fluidic relevance to the myocardial tissue. We also performed a microenvironment-controlled microfluidic cultivation of myocardial cells with high viability and regular structure integration. Using the well-established culture device with a tissue-mimicking microenvironment, a further on-chip investigation of hypoxia-induced myocardial injury was carried out and the varying apoptotic responses of myocardial cells were temporally monitored and measured. The results show that the hypoxia directionally resulted in observable cell shrinkage, disintegration of the cytoskeleton, loss of mitochondrial membrane potential, and obvious activation of caspase-3, which indicates its significant apoptosis effect on myocardial cells. We believe this microfluidic device can be suitable for temporal investigations of cell activities and responses in myocardial infarction. It is also potentially valuable to the microcontrol development of tissue-simulated studies of multiple clinical organ/tissue disease dynamics.

To evaluate the carbon and nitrogen sequestration capacity of different tillage practices, soil organic carbon and nitrogen concentrations and storages of the cultivated layer under different tillage practices (conventional tillage, no-tillage and fallow) were compared. The results showed that soil organic carbon under different tillage practices were significantly different among different soil depths and 0 – 5 cm > 5 – 15 cm > 15 – 30 cm (except for the conventional tillage in booting stage). The concentration of soil organic carbon in notillage was higher than that in conventional tillage and fallow. The concentrations of soil total nitrogen were significantly different among different treatments in 5 – 15 cm of jointing stage and 0 – 5 cm of booting and ripening stage, and no-tillage > conventional tillage > fallow. Soil organic carbon storage in the cultivated layer (0 – 30 cm) was increased by no-tillage practice, but soil nitrogen storage was not affected significantly by tillage practices. Soil organic carbon and total nitrogen were negatively correlated with pH, exchangeable K+ and Ca2+.

Microfluidic trapping methods create significant opportunities to establish highly controlled cell positioning and arrangement for the microscale study of numerous cellular physiological and pathological activities. However, a simple, straightforward, dynamic, and high-throughput method for cell trapping is not yet well established. In the present paper, we report a direct active trapping method using an integrated microfluidic device with pneumatic microstructures (PμSs) for both operationally and quantitatively dynamic localization of cells, as well as for high-throughput cell patterning. We designed and fabricated U-shape PμS arrays to replace the conventional fixed microstructures for reversible trapping. Multidimensional dynamics and spatial consistency of the PμSs were optically characterized and quantitatively demonstrated. Furthermore, we performed a systematic trapping investigation of the PμSs actuated at a pressure range of 0 psi to 20 psi using three types of popularly applied mammalian cells, namely, human lung adenocarcinoma A549 cells, human hepatocellular liver carcinoma HepG2 cells, and human breast adenocarcinoma MCF-7 cells. The cells were quantitatively trapped and controlled by the U-shape PμSs in a programmatic and parallel manner, and could be opportunely released. The trapped cells with high viability were hydrodynamically protected by the real-time actuation of specifically designed umbrella-like PμSs. We demonstrate that PμSs can be applied as an active microfluidic component for large-scale cell patterning and manipulation, which could be useful in many cell-based tissue organization, immunosensor, and high-throughput imaging and screening.

This work describes an improved method for monodispersed water-in-oil droplet formation and collection using a composite microfluidic device composed of a poly(dimethylsiloxane) (PDMS) microfluidic device and a commercially available quartz capillary. The application of the method to chemical heat-shock (CaCl2-dependent) transformation of Escherichia coli (E. coli) is also presented. With this approach, tunable and uniform different-sized droplets were generated and conveniently collected into a capillary for subsequent experiments. Characterization of droplet size and formation frequency exhibits that droplet behavior is strongly dependent on the ratio (R) of aqueous phase flow rate (Qaq) to oil phase flow rate (Qo). An increase in R induces droplet size and droplet formation frequency increase, which agrees well with a theoretical calculation. To illustrate the application of this droplet-based device in biological fields, as a case study, we also apply this device to the study of heat-shock E. coli transformation. Results demonstrate that plasmid DNA can be effectively transformed into E. coli, and a similar transformation efficiency with the traditional tube-based method can be obtained. This technique provides a new way for droplet generation and easy collection, as well as functional genomics studies by taking advantage of the high throughput of droplet microfluidics.