Simulation of droplet-based microfluidic lab-on-a-chip applications

This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.Miniaturization of biological and chemical assays in lab-on-a-chip systems is a highly topical field of research. Droplet-based microfluidic chips are types of these miniaturized systems. They expand the capability of assays with special features that are unreached by traditional workflows. In particular, small sample volumes, independent separated reaction units, high throughput, automation and parallelization of assays are prominent features of droplet-based microfluidic devices. Full custom centric design of droplet-based microfluidic lab-on-a-chip technology implicates a high system integration level and design complexity. Therefore advanced development methodologies are needed, comparable with the methods in electronic design automation. Our design and simulation toolkit meets these requirements for an agile and low-risk development of custom lab-on-a-chip devices. The system simulation approach enables a fast and precise prediction of complex microfluidic networks. This fact is confirmed by reference and benchmark experiments. The results show that the simulation correctly reproduces the experimental measurements.The German BMBF and the EU in the projects DiNaMiD, signature 0315591B and NoE Photonics4Life, Grant Agreement number: 224014

Effect of Junction Geometry on Monodispersed Microdroplet Generation in Microfluidic Aqueous Two-Phase Systems

Aqueous two-phase system (ATPS) consists of two immiscible water-based solutions of polymers, which can form phase partitioning. Dextran and polyethylene glycol I used in this thesis is the one of common components of aqueous two-phase system give a reliable and incompatible environment for purification of biomedical products and cellular macromolecules. Recently, ATPS have received increasing attention as a separation method in microfluidic device due to the advantages of biocompatibility, unlimited combination, and low interfacial tension. Hence, it became an important to discover researches related to ATPS microfluidic device. Microdroplets produced in microfluidic device are a largely interesting phenomenon for various applications. Monodisperse and size manageable microdroplets using ATPS could potentially be used to better micro-enviornment. However, extremely low interfacial tension (≤ 100 μN/m) leading to viscoelastic fluid (non-Newtonian) characteristic makes it difficult to generate microdroplets. It is necessary to control the physical and topological behavior of ATPS. Therefore, this thesis aims to study fluid mechanism for droplet-based microfluidics using ATPS. Droplet generation using aqueous two phase systems (ATPS) in microfluidic device was studied by various junction areas which were considered as T-junction, flow-focusing, and double-flow-focusing. The characteristic of low interfacial tension and high viscosity between aqueous phases was the challenge to produce uniform micro-droplets. The importance of this experiment is that in contrast to another external installations previously studied, double-flow-focusing channel drew advantages of simple method, cost effective, and heavy workload. Without the continuous mechanical pressure by pressure-driven flow, no external actuations were used. T-junctions and flow-focusing, broadly used for microfluidic device, were compared with double-flow-focusing channel. The role of each flow-focusing junction for monodisperse water-in-water (w/w) droplets was investigated. Additional flow-focusing junction for monodisperse water-in-water (w/w) droplets brought the consequence different from T-juntion and flow-focusing. Moreover, I proved that PEG and Dextran droplets within double-flow-focusing could be formed with combination of two continuous flow rates. Surfactant impact on droplet generation in ATPS was studied. Thus, a double-flow-focusing microfluidic device I developed was able to be a crucial method to generate water-in-water (w/w) droplets due to the stability of dispersion between two junction areas

Droplets Formation and Merging in Two-Phase Flow Microfluidics

Two-phase flow microfluidics is emerging as a popular technology for a wide range of applications involving high throughput such as encapsulation, chemical synthesis and biochemical assays. Within this platform, the formation and merging of droplets inside an immiscible carrier fluid are two key procedures: (i) the emulsification step should lead to a very well controlled drop size (distribution); and (ii) the use of droplet as micro-reactors requires a reliable merging. A novel trend within this field is the use of additional active means of control besides the commonly used hydrodynamic manipulation. Electric fields are especially suitable for this, due to quantitative control over the amplitude and time dependence of the signals, and the flexibility in designing micro-electrode geometries. With this, the formation and merging of droplets can be achieved on-demand and with high precision. In this review on two-phase flow microfluidics, particular emphasis is given on these aspects. Also recent innovations in microfabrication technologies used for this purpose will be discussed

Emulsion characterization via microfluidic devices : A review on interfacial tension and stability to coalescence

Emulsions have gained significant importance in many industries including foods, pharmaceuticals, cosmetics, health care formulations, paintings, polymer blends and oils. During emulsion generation, collisions can occur between newly-generated droplets, which may lead to coalescence between the droplets. The extent of coalescence is driven by properties of dispersed and continuous phases, e.g. density, viscosity, ion strength and pH, and system conditions, e.g. temperature, pressure or any external applied forces. In addition, the diffusion and adsorption behaviors of emulsifiers which govern the dynamic interfacial tension of the forming droplets, the surface potential, and the duration and frequency of the droplet collisions, contribute to the overall rate of coalescence. An understanding of these complex behaviors, particularly those of interfacial tension and droplet coalescence during emulsion generation, is critical for the design of an emulsion with desirable properties and the optimization of the processing conditions. However, in many cases, the time scales over which these phenomena occur are extremely short, typically a fraction of a second, which makes their accurate determination by conventional analytical methods extremely challenging. In the past few years, with advances in microfluidic technology, many attempts have demonstrated that microfluidic systems, characterized by micrometer-size channels, can be successfully employed to precisely characterize these properties of emulsions. In this review, current applications of microfluidic devices to determine the equilibrium and dynamic interfacial tension during the droplet formation, and to investigate the coalescence stability of dispersed droplets applicable to the processing and storage of emulsions, are discussed.Peer reviewe

Design of microfluidic networks

Microfluidics is a relatively new and fast growing research area in fluid mechanics. The devices in question are thin wafers containing etched or printed interconnecting channels through which fluids are pumped, which can mix and/or react at various nodes to produce an output product. Microfluidic devices have applications in many manufacturing and chemical detection processes. For example, they can be used to manufacture monodisperse droplets with very well defined properties for pharmaceutical applications; or form the basis for miniaturised ‘lab-on-a-chip’ sensor arrays for detecting biological substances or toxins

Droplet microfluidics: a tool for biology, chemistry and nanotechnology

The ability to perform laboratory operations on small scales using miniaturized devices provides numerous benefits, including reduced quantities of reagents and waste as well as increased portability and controllability of assays. These operations can involve reaction components in the solution phase and as a result, their miniaturization can be accomplished through microfluidic approaches. One such approach, droplet microfluidics, provides a high-throughput platform for a wide range of assays and approaches in chemistry, biology and nanotechnology. We highlight recent advances in the application of droplet microfluidics in chip-based technologies, such as single-cell analysis tools, small-scale cell cultures, in-droplet chemical synthesis, high-throughput drug screening, and nanodevice fabrication

Synthesis of functional materials by non-Newtonian microfluidic multiphase system

With increasing level of polymer solution involvement in multiphase microdevice for formation of emulsion and fabrication of functional materials, it is of paramount importance to systematically understand the relevant physics of droplet formation in non-Newtonian fluids and how the material formation process may be affected due to the complex rheological effect. The chapter aims to review and discuss the recent advances in echnologies that enable fabrication and application of functional materials formed from non-Newtonian microfluidic multiphase system. Rheological behavior of polymer solutions and the mathematical models are reviewed. The influence of microstructure on rheological behavior of polymer solutions and the fundamental physical phenomena driving non-Newtonian microfluidic multiphase system are discussed. Shear thinning and viscoelastic effect on breakup dynamics and droplet formation are presented. The microfabrication process of the device and synthesis of emulsion-templated materials with potential industrial and biochemical applications are elucidated