Centrifugal automation of a triglyceride bioassay on a low-cost hybrid paper-polymer device

We present a novel paper-polymer hybrid construct for the simple automation of fundamental microfluidic operations in a lab-on-a-disc platform. The novel design, we term a paper siphon, consists of chromatographic paper strips embedded along a siphon microchannel. The paper siphon relies on two main interplaying forces to create unique valving and liquid-sampling methods in centrifugal microfluidics. At sufficiently low speeds, the inherent wicking of the paper overcomes the rotationally induced centrifugal force to drive liquids towards inwards positions of the disc. At elevated speeds, the dominant centrifugal force will extract liquid from the siphon paper strip towards the edge of the disc. Distinct modes of flow control have been developed to account for water (reagent) and more viscous plasma samples. The system functionality is demonstrated by the automation of sequential sample preparation steps in a colorimetric triglyceride assay: plasma is metered from a whole blood sample and incubated with a specific enzymatic mixture, followed by detection of triglyceride levels through (off-disc) absorbance measurements. The successful quantification of triglycerides and the simple fabrication offer attractive directions for such hybrid devices in low-cost bioanalysis.     

Thermo-pneumatic pumping in centrifugal microfluidic platforms

The pumping of fluids in microfluidic discs by centrifugal forces has several advantages, however, centrifugal pumping only permits unidirectional fluid flow, restricting the number of processing steps that can be integrated before fluids reach the edge of the disc. As a solution to this critical limitation, we present a novel pumping technique for the centrifugal microfluidic disc platform, termed the thermo-pneumatic pump (TPP), that enables fluids to be transferred the center of a rotating disc by the thermal expansion of air. The TPP is easy to fabricate as it is a structural feature with no moving components and thermal energy is delivered to the pump via peripheral infrared (IR) equipment, enabling pumping while the disc is in rotation. In this report, an analytical model for the operation of the TPP is presented and experimentally validated. We demonstrate that the experimental behavior of the pump agrees well with theory and that flow rates can be controlled by changing how well the pump absorbs IR energy. Overall, the TPP enables for fluids to be stored near the edge of the disc and transferred to the center on demand, offering significant advantages to the microfluidic disc platform in terms of the handling and storage of liquids.     

Microfluidic integrated circuits for signal processing using analogous relationship between pneumatic microvalve and MOSFET

In this paper, a new concept and potential demonstration of functional microfluidic integrated circuits using MEMS technology are presented. The fluidic integrated circuits were constructed utilizing analogous relationship between MOSFET and pneumatic microvalve with a diaphragm structure. The signal transmitted through the circuit is the fluidic signal, that is, the pressure or the flow-rate of the fluid. The pneumatic microvalve in this study is expressed by small-signal equivalent model similar to that of a MOSFET. Small signal behavior of microfluidic integrated circuits can be expected using the model, if the parameters in the model are extracted properly from fabricated microvalves. As an example of a fluidic circuit, pressure inverting amplifiers including integrated two microvalves were fabricated and evaluated. As a result, they showed sharp pressure transfer curves similar to MOS inverter circuits. A maximum pressure gain of 32.0 dB was obtained, and it can be used for pressure amplification in analog applications. In addition, they can be used as pressure inverter logic circuits for digital applications. Although the theory and design environment of the new microvalve circuit technology have not been established yet, multifunctional fluidic analog and digital circuits can be realized for special application fields different from electronic integrated circuits.     

Vertical liquid transportation through capillary bundle structure using centrifugal force

The use of three-dimensional (3D) microstructures is becoming essential attempt to develop next generations’ microdevices, to integrate many modules and various functions, and enhance the performance of device. In this paper, we present a new concept for lab on a chip using 3D structure and centrifugal pumping for integrated functional fluid systems such as high-throughput screening, and point of care testing systems which has stacked multiple structures with 3D-interconnection. The use of 3D structure brings many benefits for above high throughput systems, such as possibility to integrate various modules enabling to perform total assay operation, from sample preparation for biochemical reaction and their detection on one platform. For this concept, the most important key technology is control of a vertical valving and transportation of liquid between different 2D micro channel networks with different height levels. We demonstrated such vertical liquid transportation in 3D micro channel networks through the high aspect ratio capillary bundle filter by controlling spinning speed of device and centrifugal force as a pumping force, and confirmed capillary bundle could be employed as vertical microvalve for 3D fluidic systems using centrifugal force as a pumping method.     

Basic study for drive mechanism with synthetic fiber rope – investigation of strength reduction by bending and terminal fixation method

In this study, we investigate physical properties of synthetic fiber ropes for drive mechanism. First, we carry out experiment about the relation between tensile strength and bending ratio D / d, where D is pulley diameter and d is rope diameter. Although it is widely known that a metal wire rope gets strength reduction under small D / d, we newly detected that a synthetic fiber rope also gets strength reduction in the same way. Secondly, we evaluate the strength of various end fixation method of synthetic fiber rope. Knot fixation makes rope strength half in all kinds of knot. Clamping fixation with enough pressuring force can get large strength even if a synthetic fiber rope has low friction coefficient. Although calking fixation and sewing fixation cannot change rope length easily, they can get the largest strength around 85–90% of the rope strength in our experiment.     

“From microtiter plates to droplets” tools for micro-fluidic droplet processing

Droplet-based microfluidic allows high throughput experimentation in with low volume droplets. Essential fluidic process steps are on the one hand the proper control of the droplet composition and on the other hand the droplet processing, manipulation and storage. Beside integrated fluidic chips, standard PTFE-tubings and fluid connectors can be used in combination with appropriate pumps to realize almost all necessary fluidic processes. The segmented flow technique usually operates with droplets of about 100–500 nL volume. These droplets are embedded in an immiscible fluid and confined by channel walls. For the integration of segmented flow applications in established research workflows—which are usually base on microtiter plates—robotic interface tools for parallel/serial and serial/parallel transfer operations are necessary. Especially dose–response experiments are well suited for the segmented flow technique. We developed different transfer tools including an automated “gradient take-up tool” for the generation of segment sequences with gradually changing composition of the individual droplets. The general working principles are introduced and the fluidic characterizations are given. As exemplary application for a dose–response experiment the inhibitory effect of antibiotic tetracycline on Escherichia coli bacteria cultivated inside nanoliter droplets was investigated.     

Elasto-plastic finite element analysis of orthotropic rotating discs with holes

The elasto-plastic stress analysis of orthotropic rotating discs with holes has been carried out by the finite element method (FEM). An isoparametric rectangular element with nine nodes has been chosen and the Lagrange polynomial has been used as interpolation function. Steel-aluminium composite has been manufactured by upsetting under the pressure and the temperature. Mechanical properties and yield strengths of composite material have been obtained experimentally by using a strain gauge in the tensile testing machine. The expansions of plastic regions have been illustrated for various cases. Residual stresses and tangential stresses have been shown on the elasto-plastic boundaries of the disc. The limit of angular velocities of the orthotropic disc have been increased by using tangential residual stresses and tangential stresses in the disc subjected to the centrifugal force.     

Asymptotic output tracking with a two level hierarchical system

In this paper a two level hierarchical system is considered. This system consists of two discs that have limited rotational movement. It is assumed that one disc has large inertia and low angular acceleration and the other disc has low inertia and high angular acceleration. The disc with large angular acceleration is mounted on the periphery of the disc with low acceleration. The angular velocity and orientation of both discs is controllable. It is shown how the theory of asymptotic output tracking for linear systems, combined with some easily programmable mathematical optimization problems leads to very good results when designing a controller for asymptotically tracking a moving object, in particular meeting the angular acceleration limits imposed on the two discs. The paradigm for this system is the human eye-head-neck system and the tracking of a moving object at a distance from the eye.     

Liquid recirculation in microfluidic channels by the interplay of capillary and centrifugal forces

We demonstrate a technique to recirculate liquids in a microfluidic channel by alternating predominance of centrifugal and capillary forces to rapidly bring the entire volume of a liquid sample to within one diffusion length, δ, of the surface, even for sample volumes hundreds of times the product of δ and the geometric device area. This is accomplished by repetitive, random sampling of an on-disc sample reservoir to form a thin fluid layer of thickness δ in a microchannel, maintaining contact for the diffusion time, then rapidly exchanging the fluid layer for a fresh aliquot by disc rotation and stoppage. With this technique, liquid volumes of microlitres to millilitres can be handled in many sizes of microfluidic channels, provided the channel wall with greatest surface area is hydrophilic. We present a theoretical model describing the balance of centrifugal and capillary forces in the device and validate the model experimentally.     

Modeling, analysis and design of centrifugal force driven transient filling flow into rectangular microchannel

Recently, centrifugal pumping has been discovered to be an excellent alternative method for controlling the fluid flow inside microchannels. In this paper, we have developed the physical modeling and carried out the analysis for the centrifugal force driven transient filling flow into a rectangular microchannel. Two types of analytic solutions for the transient flow were obtained: (1) a pseudo-static approximate solution, and (2) an exact solution. Analytic solutions include expressions for flow front advancement, detailed velocity profile and pressure distribution. The obtained analytical results show that the filling flow driven by centrifugal force is affected by three dimensionless parameters which combine fluid properties, rectangular channel geometry and processing condition of rotational speed. Effects of inertia, viscous and centrifugal forces were also discussed based on the parametric study. Furthermore, we have also successfully provided a simple and convenient analytical design tool for such rectangular microchannels, demonstrating two design application examples.     

Effects of particle–fluid coupling on particle transport and capture in a magnetophoretic microsystem

A numerical analysis is presented of the effects of particle–fluid coupling on the transport and capture of magnetic particles in a microfluidic system under the influence of an applied magnetic field. Particle motion is predicted using a computational fluid dynamic CFD-based Lagrangian–Eulerian approach that takes into account dominant particle forces as well as two-way particle–fluid coupling. Two dimensionless groups are introduced that characterize particle capture, one that scales the magnetic and hydrodynamic forces on the particle and another that scales the distance to the magnetic field source. An analysis is preformed to parameterize capture efficiency with respect to the dimensionless numbers for both one-way and two-way particle–fluid coupling. For one-way coupling, in which the flow field is uncoupled from particle motion, correlations are developed that provide insight into system performance towards optimization. The difference in capture efficiency for one-way versus two-way coupling is analyzed and quantified. The analysis demonstrates that one-way coupling, in the dilute limit, provides a conservative estimate of capture efficiency in that it overpredicts the magnetic force needed to ensure particle capture as compared with a more rigorous fully coupled analysis. In two-way coupling there is a cooperative effect between the magnetic force and a particle-induced fluidic force that enhances capture efficiency. Thus, while one-way coupling is useful for rapid parametric screening of particle capture performance, more accurate predictions require two-way particle–fluid coupling. This is especially true when considering higher capture efficiencies and/or higher particle concentrations.     

Workspace analysis of a 6-DOF cable-driven parallel robot considering pulley bearing friction under ultra-high acceleration

Cable robots can generate high velocities and accelerations due to the very small inertia of the end-effector. Therefore, CDPRs have been used widely in special industrial applications requiring high dynamics. However, the high acceleration generated affects the wrench-feasible workspace of a CDPR system significantly. In addition, as a pulley rotates, the frictional force at the pulley bearing disturbs the motion, changes the cable tensions. Thus, pulley bearing friction cannot be neglected in ultra-high acceleration systems where high tensions are imposed. A workspace analysis was carried out for a wrench-feasible condition in a 6-DOF CDPR system considering the pulley bearing friction connected in series. Then, the pulley bearing friction was modeled with the Coulomb friction model including the variation of wrapping angle of pulley and a loss factor. The simulated tension profiles considering pulley bearing friction were in good agreement with data measured with a load cell. And a wrench-feasible workspace analysis under various accelerations was carried out. In conclusion, as the external acceleration was increased, the whole tension was increased and workspaces to exceed available tension occurred in case of 100 m/s². And the pulley bearing force increased or decreased the cable tension because of the direction of the signum function. As a result, the wrench-feasible workspace was changed in the presence of pulley bearing force effects.

     

Finite element analysis of V-ribbed belt/pulley system with pulley misalignment using a neural-network-based material model

Pulley misalignment limits the performance of V-ribbed belt/pulley system as it relates to rib load-sharing and contact pressure distribution for multiple rib belts required in high torque demands of modern automotive applications. In this paper, a three-dimensional dynamic finite element model is built to evaluate the effects of pulley misalignment. The model consists of a pulley and a segment of V-ribbed belt in contact with the pulley. A material model of belt, including rubber compound and reinforcing cord is developed. Multiple rubber layers are each considered hyperelastic with distinct material characterization parameters. A novel neural-network-based hyperelastic material model is implemented to represent properties of nonlinear elastic belt-rib compound. The models are implemented in the commercial code ABAQUS/Explicit to simulate the misalignment of the belt–pulley system. The developed model is first validated by experimental measurements of pulley lateral force due to misalignment. Also, three common types of misalignment in the belt–pulley system are analyzed and results are presented.     

Modeling, analysis and design of centrifugal force-driven transient filling flow into a circular microchannel

Recently, centrifugal pumping has been regarded as an excellent alternative control method for fluid flow inside microchannels. In this paper, we have first developed the physical modeling and carried out the analysis for the centrifugal force-driven transient filling flow into a circular microchannel. Two types of analytic solutions for the transient flow were obtained: (1) pseudostatic approximate solution and (2) exact solution. Analytic solutions include expressions for flow front advancement, detailed velocity profile and pressure distribution. The obtained analytic results show that the filling flow driven by centrifugal force is affected by two dimensionless parameters which combine fluid properties, channel geometry and processing condition of rotational speed. Effects of inertia, viscous and centrifugal forces were also discussed based on the parametric study. Furthermore, we have also successfully provided a simple and convenient analytic design tool for such microchannels, demonstrating two design application examples.     

Secure Information Access Strategy for a Virtual Data Centre

With the arrival of on-demand computing, data centre requirements are extensive, with fluid boundaries. Loaded Internet applications, service-oriented architectures, virtualization and security provisioning are the major operations of a data centre. Security is an absolute necessity of any network architecture, and the virtual IT data centre is no exception. At the boundary, security is focused on securing the terminals of the data centre from external threats and providing a secure gateway to the Internet. The paradigm shift towards a new computing environment makes communications more complicated for Infrastructure Providers (InP). This complexity includes the security of the data centre’s components to protect data from malicious attacks or from being compromised. Threats/attacks are inevitable if the data are generated from a public network, such as Wi-Fi in an Airport, Railway station and other public places. Since these places create enormous amounts of data from anonymous and naive users, it is essential to store the information in a data centre. In this article, we propose an efficient, secure, and privacy-preservation information access algorithm to access data centres in public wifi networks. This algorithm is based on the primitive root approach for sending and receiving credentials through the anonymous authentication of the users and ensuring protected data access from the data centre. Security and Performance Analysis and its evaluation prove that our approach is successful with respect to security, privacy preservation and computational complexity.     

High aspect ratio tapered hollow metallic microneedle arrays with microfluidic interconnector

We present a novel microfabrication method for a tapered hollow metallic microneedle array and its complete microfluidic packaging for drug delivery and body fluid sampling applications. Backside exposure of SU-8 through a UV transparent substrate was investigated as a means of fabricating a dense array of tall (up to 400 μm) uniformly tapered SU-8 pillar structures with angles in the range of 3.1–5° on top of the SU-8 mesa. Conformal electroplating of metals on top of the array of the tapered SU-8 pillars, lapping of the tip of the metallic microneedles with planarizing polymer, and removal of the SU-8 sacrificial layers resulted in an array of tapered hollow metallic microneedles with a fluidic reservoir on the backside. A microfluidic interconnector assembly was designed and fabricated using SU-8 and conventionally machined PMMA in a way that it has a male interconnector, which directly fits into the fluidic reservoir of the microneedle array at one end and the other male interconnector, which provides fluidic interconnection to external devices at the other end. The fluid flow rate was measured and it showed 0.69 μL/s. per microneedle when the pressure of 6.89 KPa (1 psi) was applied.     

Topology optimization of steady and unsteady incompressible Navier–Stokes flows driven by body forces

This paper presents the topology optimization method for the steady and unsteady incompressible Navier–Stokes flows driven by body forces, which typically include the constant force (e.g. the gravity) and the centrifugal and Coriolis forces. In the topology optimization problem, the artificial friction force with design variable interpolated porosity is added into the Navier–Stokes equations as the conventional method, and the physical body forces in the Navier–Stokes equations are penalized using the power-law approach. The topology optimization problem is analyzed by the continuous adjoint method, and solved by the finite element method in conjunction with the gradient based approach. In the numerical examples, the topology optimization of the fluidic channel, mass distribution of the flow and local velocity control are presented for the flows driven by body forces. The numerical results demonstrate that the presented method achieves the topology optimization of the flows driven by body forces robustly.     

Digital microfluidics: is a true lab-on-a-chip possible?

The suitability of electrowetting-on-dielectric (EWD) microfluidics for true lab-on-a-chip applications is discussed. The wide diversity in biomedical applications can be parsed into manageable components and assembled into architecture that requires the advantages of being programmable, reconfigurable, and reusable. This capability opens the possibility of handling all of the protocols that a given laboratory application or a class of applications would require. And, it provides a path toward realizing the true lab-on-a-chip. However, this capability can only be realized with a complete set of elemental fluidic components that support all of the required fluidic operations. Architectural choices are described along with the realization of various biomedical fluidic functions implemented in on-chip electrowetting operations. The current status of this EWD toolkit is discussed. However, the question remains: which applications can be performed on a digital microfluidic platform? And, are there other advantages offered by electrowetting technology, such as the programming of different fluidic functions on a common platform (reconfigurability)? To understand the opportunities and limitations of EWD microfluidics, this paper looks at the development of lab-on-chip applications in a hierarchical approach. Diverse applications in biotechnology, for example, will serve as the basis for the requirements for electrowetting devices. These applications drive a set of biomedical fluidic functions required to perform an application, such as cell lysing, molecular separation, or analysis. In turn, each fluidic function encompasses a set of elemental operations, such as transport, mixing, or dispensing. These elemental operations are performed on an elemental set of components, such as electrode arrays, separation columns, or reservoirs. Examples of the incorporation of these principles in complex biomedical applications are described.     

Immigration and future housing needs in Switzerland: Agent-based modelling of agglomeration Lausanne

Immigration accounts for 80% of Switzerland's annual population growth, and therefore profoundly impacts demographics, and the attendant housing needs. As there are different possible future scenarios of immigration that will impact urban transformation in Switzerland, we have developed an agent-based dwellings model that, with reasonable computing time due to the use of the computer architecture of graphical processor units, can simulate for a time horizon of decades, the annual evolution of millions of individually characterised households. This dwellings model is coupled to an agent-based population model that simulates millions of individual population agents. We simulate different immigration scenarios, up to 2035, in the Swiss agglomeration of Lausanne. It is shown that the building capacity of the city of Lausanne will reach a limit in 2022, subsequently leading to more rapid growth in the periphery of the agglomeration Lausanne. The construction of new residential dwellings consists primarily of smaller apartments that are more attractive to the demographic of smaller households; this demographic tends to move to the periphery. As families tend to move towards the city centre due to the availability of services, the city and periphery show opposite evolutions over time in the numbers of family households compared to numbers of singles and couples households. The periphery requires an increase in the number and typology of services targeted at the growing demographic of smaller households. Further as most workplaces are still be located in the city centre, the planned improvement of transportation infrastructure in the agglomeration should primarily focus on improved access to the periphery. These observations underline the profound impact of the typology of immigration on the demand for suitable housing, and thus on urban development.     

An environment to develop parallel code for solving partial differential equations based-problems

Since the beginning of computing, the use of computers to simulate physical phenomena has been a driving force to advance the field of computing. Computational scientists demand more computational power and more facility to implement applications. The conventional library interface does not hide the complexity of the underlying parallel architectures and their programming paradigms from users. Our investigation group is currently implementing an environment for solving partial differential equations (PDEs). Using this high-level tool the user can easily develop parallel applications for solving PDEs based problems using multigrid techniques without knowledge on the underlying computer hardware or software. This paper provides the first steps towards the creation of the environment.