A microfluidic platform for size-dependent generation of droplet interface bilayer networks on rails

Droplet interface bilayer (DIB) networks are emerging as a cornerstone technology for the bottom up construction of cell-like and tissue-like structures and bio-devices. They are an exciting and versatile model-membrane platform, seeing increasing use in the disciplines of synthetic biology, chemical biology, and membrane biophysics. DIBs are formed when lipid-coated water-in-oil droplets are brought together—oil is excluded from the interface, resulting in a bilayer. Perhaps the greatest feature of the DIB platform is the ability to generate bilayer networks by connecting multiple droplets together, which can in turn be used in applications ranging from tissue mimics, multicellular models, and bio-devices. For such applications, the construction and release of DIB networks of defined size and composition on-demand is crucial. We have developed a droplet-based microfluidic method for the generation of different sized DIB networks (300–1500 pl droplets) on-chip. We do this by employing a droplet-on-rails strategy where droplets are guided down designated paths of a chip with the aid of microfabricated grooves or “rails,” and droplets of set sizes are selectively directed to specific rails using auxiliary flows. In this way we can uniquely produce parallel bilayer networks of defined sizes. By trapping several droplets in a rail, extended DIB networks containing up to 20 sequential bilayers could be constructed. The trapped DIB arrays can be composed of different lipid types and can be released on-demand and regenerated within seconds. We show that chemical signals can be propagated across the bio-network by transplanting enzymatic reaction cascades for inter-droplet communication.     

Microfluidic electrical sorting of particles based on shape in a spiral microchannel

Shape is an intrinsic marker of cell cycle, an important factor for identifying a bioparticle, and also a useful indicator of cell state for disease diagnostics. Therefore, shape can be a specific marker in label-free particle and cell separation for various chemical and biological applications. We demonstrate in this work a continuous-flow electrical sorting of spherical and peanut-shaped particles of similar volumes in an asymmetric double-spiral microchannel. It exploits curvature-induced dielectrophoresis to focus particles to a tight stream in the first spiral without any sheath flow and subsequently displace them to shape-dependent flow paths in the second spiral without any external force. We also develop a numerical model to simulate and understand this shape-based particle sorting in spiral microchannels. The predicted particle trajectories agree qualitatively with the experimental observation.     

Microfluidic production of single micrometer-sized hydrogel beads utilizing droplet dissolution in a polar solvent

In this study, a microfluidic process is proposed for preparing monodisperse micrometer-sized hydrogel beads. This process utilizes non-equilibrium aqueous droplets formed in a polar organic solvent. The water-in-oil droplets of the hydrogel precursor rapidly shrunk owing to the dissolution of water molecules into the continuous phase. The shrunken and condensed droplets were then gelled, resulting in the formation of hydrogel microbeads with sizes significantly smaller than the initial droplet size. This study employed methyl acetate as the polar organic solvent, which can dissolve water at 8%. Two types of monodisperse hydrogel beads—Ca-alginate and chitosan—with sizes of 6–10 μm (coefficient of variation < 6%) were successfully produced. In addition, we obtained hydrogel beads with non-spherical morphologies by controlling the degree of droplet shrinkage at the time of gelation and by adjusting the concentration of the gelation agent. Furthermore, the encapsulation and concentration of DNA molecules within the hydrogel beads were demonstrated. The process presented in this study has great potential to produce small and highly concentrated hydrogel beads that are difficult to obtain by using conventional microfluidic processes.     

Microfluidic size separation of cells and particles using a swinging bucket centrifuge

Biomolecular separation is crucial for downstream analysis. Separation technique mainly relies on centrifugal sedimentation. However, minuscule sample volume separation and extraction is difficult with conventional centrifuge. Furthermore, conventional centrifuge requires density gradient centrifugation which is laborious and time-consuming. To overcome this challenge, we present a novel size-selective bioparticles separation microfluidic chip on a swinging bucket minifuge. Size separation is achieved using passive pressure driven centrifugal fluid flows coupled with centrifugal force acting on the particles within the microfluidic chip. By adopting centrifugal microfluidics on a swinging bucket rotor, we achieved over 95% efficiency in separating mixed 20 μm and 2 μm colloidal dispersions from its liquid medium. Furthermore, by manipulating the hydrodynamic resistance, we performed size separation of mixed microbeads, achieving size efficiency of up to 90%. To further validate our device utility, we loaded spiked whole blood with MCF-7 cells into our microfluidic device and subjected it to centrifugal force for a mere duration of 10 s, thereby achieving a separation efficiency of over 75%. Overall, our centrifugal microfluidic device enables extremely rapid and label-free enrichment of different sized cells and particles with high efficiency.     

短期生产函数的线性估计与非线性估计比较

利用西方经济学的厂商理论和计量经济学的知识探讨了如何对短期生产函数进行有效的估计。以短期生产函数具备的理论特征为标准，分别观察线性估计与非线性估计二者对这些特征的拟合程度，从而优化短期生产函数的估计形式。最后给出了具体的短期生产函数的线性化估计方法，以及专业统计软件的具体实现方式。     

Towards the minimum-cost control of target nodes in directed networks with linear dynamics

Determining an input matrix, i.e., locating predefined number of nodes (named “key nodes”) connected to external control sources that provide control signals, so as to minimize the cost of controlling a preselected subset of nodes (named “target nodes”) in directed networks is an outstanding issue. This problem arises especially in large natural and technological networks. To address this issue, we focus on directed networks with linear dynamics and propose an iterative method, termed as “L₀-norm constraint based projected gradient method” (LPGM) in which the input matrix B is involved as a matrix variable. By introducing a chain rule for matrix differentiation, the gradient of the cost function with respect to B can be derived. This allows us to search B by applying probabilistic projection operator between two spaces, i.e., a real valued matrix space R^N?×?M and a L₀ norm matrix space $R_{L_0}^{N\times M}$ by restricting the L₀ norm of B as a fixed value of M. Then, the nodes that correspond to the M nonzero elements of the obtained input matrix (denoted as $B^{L_0}$) are selected as M key nodes, and each external control source is connected to a single key node. Simulation examples in real-life networks are presented to verify the potential of the proposed method. An interesting phenomenon we uncovered is that generally the control cost of scale free (SF) networks is higher than Erdos-Renyi (ER) networks using the same number of external control sources to control the same size of target nodes of networks with the same network size and mean degree. This work will deepen the understanding of optimal target control problems and provide new insights to locate key nodes for achieving minimum-cost control of target nodes in directed networks.     

Linear conversion of pressure into concentration, rapid switching of concentration, and generation of linear ramps of concentration in a microfluidic device

Mixing of liquids to produce solutions with different concentrations is one of the basic functionalities of microfluidic devices. Generation of specific temporal patterns of concentration in microfluidic devices is an important technique to study responses of cells and model organisms to variations in the chemical composition of their environment. Here, we present a simple microfluidic network that linearly converts pressure at an inlet into concentration of a soluble reagent in an observation region and also enables independent concurrent linear control of concentrations of two reagents. The microfluidic device has an integrated mixer channel with chaotic three-dimensional flow that facilitates rapid switching of concentrations in a continuous range. A simple pneumatic setup generating linear ramps of pressure is used to produce smooth linear ramps and triangular waves of concentration with different slopes. The use of chaotic vs. laminar mixers is discussed in the context of microfluidic devices providing rapid switching and generating temporal waves of concentration.     

A fuzzy linear programming model for the optimization of multi-stage supply chain networks with triangular and trapezoidal membership functions

Supply chain management (SCM) is concerned with a complex business relations network that contains interrelationships between various entities, such as suppliers, manufacturers, distribution centers and customers. SCM integrates these entities and manages their interrelationships through the use of information technology to meet customer expectations (i.e., higher product variety and quality, lower costs and faster responses) effectively along the entire value chain. Thus, one of the vital issues in supply chain management is the design of the value chain network. In this paper, a fuzzy linear programming model for the optimization of the multi-stage supply chain model with triangular and trapezoidal membership functions is presented. The model determines the fuzzy capacities of the facilities (plants or distribution centers (DCs)) and the design of the network configuration with a minimum total cost. The total cost involves the shipping cost from suppliers; transportation costs between plants and DCs; distribution costs between DCs and customer zones; and opportunity costs from not having the material at the right time. The developed model is solved by a professional software package (LINDO), and the computational results are discussed.     

Microfluidic wet spinning of chitosan-alginate microfibers and encapsulation of HepG2 cells in fibers

The successful encapsulation of human hepatocellular carcinoma (HepG2) cells would greatly assist a broad range of applications in tissue engineering. Due to the harsh conditions during standard chitosan fiber fabrication processes, encapsulation of HepG2 cells in chitosan fibers has been challenging. Here, we describe the successful wet-spinning of chitosan-alginate fibers using a coaxial flow microfluidic chip. We determined the optimal mixing conditions for generating chitosan-alginate fibers, including a 1:5 ratio of 2% (w∕w) water-soluble chitosan (WSC) solution to 2% (w∕w) alginate solution. Ratio including higher than 2% (w∕w) WSC solution increased aggregation throughout the mixture. By suspending cells in the WSC-alginate solution, we successfully fabricated HepG2 cell-laden fibers. The encapsulated HepG2 cells in the chitosan-alginate fibers were more viable than cells encapsulated in pure alginate fibers, suggesting that cross-linked chitosan provides a better environment for HepG2 cells than alginate alone. In addition, we found that the adhesion of HepG2 cells on the chitosan-alginate fiber is much better than that on the alginate fibers.     

BRCA patients and clinical collectives: new configurations of action in cancer genetics practices

Since the late 1980s, in France and in a number of other countries, cancer genetics testing has become a clinical reality, particularly for hereditary breast and ovarian cancer. BRCA tests allowing for the assessment of an increased cancer risk among patients and their healthy relatives are now being routinely performed as part of clinical practice. Based on fieldwork on French clinical cancer genetics and on the French Cancer Genetics Collaborative Network, this paper examines the configuration of entities, actors and activities mobilized by the performance of BRAC testing, and argues that the development of clinical molecular genetic practices is predicated upon the development of new forms of collaborative work that lead to a transformation of the content and organization of medical activities and judgements. The paper analyses three major collective configurations - local multidisciplinary collectives, data collectives and new clinical collectives - and argues that they not only provide the material conditions needed to carry out the relevant activities, but also articulate a series of distinctive bio-clinical interventions. These interventions provide an interface with research activities, produce the epidemiological measurements and tools that are a sine qua non for clinical work in this field, and, most importantly, establish the conventions that underlie practices, which define the criteria that turn tools and novel entities into operational components of clinical settings. It thus appears that in the field of clinical cancer genetics, bioclinical collectives, as a locus of expertise, have replaced the individual judgement of the practicing clinician.     

Microfluidic model of monocyte extravasation reveals the role of hemodynamics and subendothelial matrix mechanics in regulating endothelial integrity

Extravasation of circulating cells is an essential process that governs tissue inflammation and the body''s response to pathogenic infection. To initiate anti-inflammatory and phagocytic functions within tissues, immune cells must cross the vascular endothelial barrier from the vessel lumen to the subluminal extracellular matrix. In this work, we present a microfluidic approach that enables the recreation of a three-dimensional, perfused endothelial vessel formed by human endothelial cells embedded within a collagen-rich matrix. Monocytes are introduced into the vessel perfusate, and we investigate the role of luminal flow and collagen concentration on extravasation. In vessels conditioned with the flow, increased monocyte adhesion to the vascular wall was observed, though fewer monocytes extravasated to the collagen hydrogel. Our results suggest that the lower rates of extravasation are due to the increased vessel integrity and reduced permeability of the endothelial monolayer. We further demonstrate that vascular permeability is a function of collagen hydrogel mass concentration, with increased collagen concentrations leading to elevated vascular permeability and increased extravasation. Collectively, our results demonstrate that extravasation of monocytes is highly regulated by the structural integrity of the endothelial monolayer. The microfluidic approach developed here allows for the dissection of the relative contributions of these cues to further understand the key governing processes that regulate circulating cell extravasation and inflammation.     

产业网络的复杂性研究与实证

本文从复杂网络的角度提出了产业网络的三个层次的复杂性水平:要素、联系和系统动力学。通过对三个层次复杂性水平的分析得到,企业在产业网络中的地位是不同的,而且产业网络是一个具有无标度特性的复杂网络。本文还给出了产业网络的宏观和微观系统动力学模型,同时应用中国半导体产业网络对复杂性进行了实证。最后,得出结论:成员之间联系的本质和动态特性是产业网络复杂性的关键方面。     

The dynamics and stability of lubricating oil films during droplet transport by electrowetting in microfluidic devices

The operation of digital microfluidic devices with water droplets manipulated by electrowetting is critically dependent on the static and dynamic stability and lubrication properties of the oil films that separate the droplets from the solid surfaces. The factors determining the stability of the films and preventing surface fouling in such systems are not yet thoroughly understood and were experimentally investigated in this study. The experiments were performed using a standard digital microfluidic cartridge in which water droplets enclosed in a thin, oil-filled gap were transported over an array of electrodes. Stable, continuous oil films separated the droplets from the surfaces when the droplets were stationary. During droplet transport, capillary waves formed in the films on the electrode surfaces as the oil menisci receded. The waves evolved into dome-shaped oil lenses. Droplet deformation and oil displacement caused the films at the surface opposite the electrode array to transform into dimples of oil trapped over the centers of the droplets. Lower actuation voltages were associated with slower film thinning and formation of fewer, but larger, oil lenses. Lower ac frequencies induced oscillations in the droplets that caused the films to rupture. Films were also destabilized by addition of surfactants to the oil or droplet phases. Such a comprehensive understanding of the oil film behavior will enable more robust electrowetting-actuated lab-on-a-chip devices through prevention of loss of species from droplets and contamination of surfaces at points where films may break.     

不确定环境下本地与跨区域网络对集群企业创新影响研究

不确定环境下本地和跨区域双重学习网络的动态平衡对集群企业创新具有积极影响。通过对浙江省温州市184家集群企业的问卷调查和实证检验,研究发现:本地和跨区域学习网络显著正向影响集群企业创新,两种网络存在显著的替代效应,且两者动态平衡能够增强双重网络的创新贡献,实现创新效应最大化;行业环境负向调节本地网络和集群企业创新,而政策环境呈现正向调节,且调节的边际效应趋于减弱。研究建议,集群企业创新需要动态平衡构建本地和跨区域学习网络,政府政策支持需适度,且需重视行业要素建设以降低行业环境不确定性,从而促进集群企业创新。     

主动实时数据库在数字矿山中的应用

为实现数字矿山建设中对实时监控和自动控制的较高要求,提出将主动实时数据库应用到数字矿山系统中,这样便可以实现系统的主动反应能力。在介绍了主动实时数据库的概念和关键技术的基础上分析了数字矿山的系统构成,构造了数字矿山系统中主动实时数据库系统模型,提出了在数字矿山系统中通过在原有系统上进行改造等有效途径来实现主动实时数据库系统,并在项目实践中得到较好的应用。     

Interfirm networks in periods of technological turbulence and stability

This paper examines how network relations between firms influence firm survival by explicitly addressing the moderating role of changing technological regimes. Using longitudinal data on 1385 developers and 190 publishers of video games in the global video game industry between 1972 and 2007, the analyses show that the effect of network ties between developers and publishers on the survival probability of developers is moderated by the level of technological turbulence in the industry. The results show that the effect of network partner failure on firm survival is dependent on the strength of ties. The failure of strongly tied network partners harms developers in stable periods and benefits them in turbulent eras, while no such relation is found for weakly tied network partners. Network partner diversity positively affects firm performance in epochs of technological turbulence, while the effect plays no significant role for firm survival in stable settings. The results indicate that the relation between interfirm network relations and firm survival are moderated by sequences of technological renewal in the video game industry which causes the industry to go through an evolution that deviates from the typical S-shaped trajectory found in industries that are characterized by strong path-dependent processes.     

A microfluidic platform for real-time and in situ monitoring of virus infection process

Microfluidic chip is a promising platform for studying virus behaviors at the cell level. However, only a few chip-based studies on virus infection have been reported. Here, a three-layer microfluidic chip with low shear stress was designed to monitor the infection process of a recombinant Pseudorabies virus (GFP-PrV) in real time and in situ, which could express green fluorescent protein during the genome replication. The infection and proliferation characteristics of GFP-PrV were measured by monitoring the fluorescence intensity of GFP and determining the one-step growth curve. It was found that the infection behaviors of GFP-PrV in the host cells could hardly be influenced by the microenvironment in the microfluidic chip. Furthermore, the results of drug inhibition assays on the microfluidic chip with a tree-like concentration gradient generator showed that one of the infection pathways of GFP-PrV in the host cells was microtubule-dependent. This work established a promising microfluidic platform for the research on virus infection.     

Technological agglomeration and the emergence of clusters and networks in nanotechnology

Research and development at the nanoscale requires a large degree of integration, from convergence of research disciplines in new fields of enquiry to new linkages between start-ups, regional actors and research facilities. Based on the analysis of two clusters in nanotechnologies (MESA+ (Twente) and other centres in The Netherlands and Minatec in Grenoble in France), the paper discusses the phenomenon of technological agglomeration: co-located scientific and technological fields associated to coordinated technology platforms to some extent actively shaped by institutional entrepreneurs. Such co-location and coordination are probably a pre-requisite for the emergence of strong nanoclusters.     

Role of knowledge conversion and social networks in team performance

This study aims to find out how different processes of knowledge management and patterns of social networking affect team performance. Our data on teams originate from a sample of different organizations from a variety of both public and private industries in Finland (76 teams; 499 employees). One of the main deficiencies in the current literature on knowledge and networks is that they tend to concentrate on specific types of teams in a single organization context. Our aim was to put the team phenomenon into an everyday context by analysing the interplay of knowledge creation and social networks in teams which function on a permanent basis in a variety of industry contexts. Both knowledge creation and social networking contributed to performance, but the results showed that whereas team members see the knowledge conversion processes as central to performance, top management emphasize the importance of social networks in value creation. In our examination, lively interaction between team members, combined with team leaders’ intra-organizational networks, contributed to team performance.