A microfluidics device to monitor platelet aggregation dynamics in response to strain rate micro-gradients in flowing blood

This paper reports the development of a platform technology for measuring platelet function and aggregation based on localized strain rate micro-gradients. Recent experimental findings within our laboratories have identified a key role for strain rate micro-gradients in focally triggering initial recruitment and subsequent aggregation of discoid platelets at sites of blood vessel injury. We present the design justification, hydrodynamic characterization and experimental validation of a microfluidic device incorporating contraction–expansion geometries that generate strain rate conditions mimicking the effects of pathological changes in blood vessel geometry. Blood perfusion through this device supports our published findings of both in vivo and in vitro platelet aggregation and confirms a critical requirement for the coupling of blood flow acceleration to downstream deceleration for the initiation and stabilization of platelet aggregation, in the absence of soluble platelet agonists. The microfluidics platform presented will facilitate the detailed analysis of the effects of hemodynamic parameters on the rate and extent of platelet aggregation and will be a useful tool to elucidate the hemodynamic and platelet mechano-transduction mechanisms, underlying this shear-dependent process.

Dielectrophoretically tuneable optical waveguides using nanoparticles in microfluidics

We present a tuneable optical waveguide using dielectrophoretically controlled nanoparticles in microfluidics. Silicon dioxide nanoparticles of different sizes in de-ionized water are channelled through a microfluidic system. An array of microelectrodes generates the dielectrophoretic force to funnel nanoparticles, forming narrowbands at the center of the microfluidics at different applied voltages and frequencies. It is observed that these narrowbands either scatter or guide the coupled light under selected conditions. The realization of such a system offers exciting possibilities for the development of a new class of optofluidics, which are tuned by the positioning of nanoparticles on demand.

Tuneable optical waveguide based on dielectrophoresis and microfluidics

In this work, an array of dielectrophoretic curved microelectrodes patterned in a microfluidic channel and integrated with a multimode rib polymeric waveguide is demonstrated. The microfluidic channel is infiltrated with suspended silica (SiO2) and tungsten trioxide (WO3) nanoparticles. The optofluidic system is found to be sensitive and responds not only to the infiltration of nanoparticle suspensions in the microfluidic channel, but also to the magnitude and frequencies of dielectrophoretic forces applied on the nanoparticles. The nanoparticles can be uniformly concentrated or repelled from the region between the curved microelectrode tips forming either a dense stream of flowing nanoparticles or a region void of nanoparticles in the evanescent sensitive region of the polymeric waveguide. The concentration and repulsion of nanoparticles from this region creates a refractive index gradient in the upper cladding of the polymeric waveguide. These conditions made it possible for light to either remain guided or be scattered as a function of dielectrophoretic settings applied on the nanoparticles. The results demonstrate that we successfully developed a novel tuneable polymeric waveguide based on dielectrophoretic assembly of nanoparticles suspended in fluids.

Thermal analysis of nanofluids in microfluidics using an infrared camera

We present the thermal analysis of liquid containing Al2O3 nanoparticles in a microfluidic platform using an infrared camera. The small dimensions of the microchannel along with the low flow rates (less than 120 μl min−1) provide very low Reynolds numbers of less than 17.5, reflecting practical parameters for a microfluidic cooling platform. The heat analysis of nanofluids has never been investigated in such a regime, due to the deficiencies of conventional thermal measurement systems. The infrared camera allows non-contact, three dimensional and high resolution capability for temperature profiling. The system was studied at different w/w concentrations of thermally conductive Al2O3 nanoparticles and the experiments were in excellent agreement with the computational fluid dynamics (CFD) simulations.

Lab-on-a-Chip turns soft : computer-aided, software-enabled microfluidics design

The current practice of designing microfluidic Lab-on-a-Chip (LoCs) limits reusing designs and makes sharing tasks among researchers difficult. One way to achieve that objective is to borrow best practices from engineering. Also it takes a lot of skills to design LoCs. Design-by-assembly in which a LoC can be designed by configuring, laying out subsystems can help new researchers to develop custom chips. Flexible, reusable, and rapid-prototyping-feasible LoC designs can be achieved by fabricated modular microfluidic blocks. However, challenging problems still persist, which limit the usefulness of prefabricated blocks. We propose software microfluidic modules (SoftMABs) based design technique to solve issues fabricated modules face. By configuring SoftMABs, integrating them, the new assembly of SoftMABs can form a 3D LoC design ready to be prototyped. The proposed method can make designing a complex LoC less challenging, and collaborating among laboratories easier. We created SoftMABs and designed a custom microfluidic chip by assembling SoftMABs like LEGOs, dragging-and-dropping them. Later we reconfigured them - by replacing a SoftMAB with another module - to make a new LoC. We believe this computeraided method is an interesting and useful LoC design technique.

Fluid mixing in droplet-based microfluidics with a serpentine microchannel

The hydrodynamics and mixing process within droplets travelling along a three dimensional serpentine microchannel are studied using a computational fluid dynamics simulation based on the volume-of-fluid approach. The fluid mixing within the droplet follows symmetric circulations in the straight section, which generates axial mixing. In the winding section, the asymmetric circulations lead to the reorientation of the fluids within the droplet, thus enhancing the mixing efficiency. The mixing performance is controlled by the spatial distribution of the mixing components and the circulation period within the droplet. The best mixing occurs when the droplet size is comparable with the channel width. When the droplet size is less than two times the channel width, the asymmetric circulations make it easy for the fluid to distribute in the axial direction, which leads to a fast mixing process. For larger droplets, the long circulation period becomes more significant, which causes lower mixing efficiency.

Optical microsensor for counting food substance particles in lab-on-a-chips

Integrated optical detection is considered to be an important operation in lab-on-a-chips. This paper presents an optical fiber-based micro-sensor that is capable of detecting food substance particles in a lab-on-a-chip. The system consists of a microcontroller and associated circuitry, a laser emitter, a laser receiver, fiber optic cables, a microfluidics chip, and the food substance samples to be tested. When the particles flow through the microfluidic channel in the chip, the receiver’s output voltage varies due to the particles blocking the passage of the laser ray. The changes in the collected signals are analyzed to count the number of particles. Experiments are conducted on several food substance samples including talcum powder, ground ginger, and soy sauce. The experimental results are presented and discussed.

Dielectrophoretic manipulation and separation of microparticles using curved microelectrodes

This paper presents the development and experimental analysis of a dielectrophoresis (DEP) system, which is used for the manipulation and separation of microparticles in liquid flow. The system is composed of arrays of microelectrodes integrated to a microchannel. Novel curved microelectrodes are symmetrically placed with respect to the centre of the microchannel with a minimum gap of 40 mm. Computational fluid dynamics method is utilised to characterise the DEP field and predict the dynamics of particles. The performance of the system is assessed with microspheres of 1, 5 and 12 mm diameters. When a high-frequency potential is applied to microelectrodes a spatially varying electric field is induced in the microchannel, which creates the DEP force. Negative-DEP behaviour is observed with particles being repelled from the microelectrodes. The particles of different dimensions experience different DEP forces and thus settle to separate equilibrium zones across the microchannel. Experiments demonstrate the capability of the system as a field flow fraction tool for sorting microparticles according to their dimensions and dielectric properties.

Dielectrophoresis for manipulation of micro/nano particles in microfluidic systems

Dielectrophoretic (DEP) force is exerted when a neutral particle is polarized in a non-uniform electric field, and depends on the dielectric properties of the particle and the suspending medium. The integration of DEP and microfluidic systems offers numerous applications for the separation, trapping, assembling, transportation, and characterization of micro/nano particles. This article reviews the applications of DEP forces in microfluidic systems. It presents the theory of dielectrophoresis, different configurations, and the applications of such systems for particle manipulation and device fabrication.

A microfluidic electroosmotic mixer and the effect of potential and frequency on its mixing efficiency

This paper presents the design and numerical simulation of a T-shape microfluidic electroosmotic micromixer. It is equipped with six microelectrodes that are embedded in the side surfaces of the microchannel. The electrode array consists of two sets of three 20 ¿m and 60 ¿m microelectrodes arranged in the form of two opposing triangles. Numerical analysis of electric potential and frequency effects on mixing efficiency of the micromixer is carried out by means of two sets of simulations. First, the electric potential is kept at 2 V while the frequency is varied within 10-50 Hz. The highest achieved mixing efficiency is 96% at 22 Hz. Next, the frequency is kept at 30 Hz whilst the electric potential is varied within 1-5 V. The best achieved mixing efficiency is 97% at 3 V.

Characterization of high fluid strain micro contractions to study the stress on biological fluids

Microfluidics has the potential to enhance the understanding of the biological fluids under strain, due to the laminar nature of the fluid and the possibility to mimic the real conditions. We present advances on charaterization of a microfluidic platform to study high strain rate flows in the transport of biological fluids. These advances are improvements on the reproduction of a  constant extensional strain rate using micro contractions and development of 3D numerical models. The micro geometries have been fabricated in polydimethyl siloxame (PDMS) using standard soft-lithography techniques with a photolithographically patterned mold. A comparison of some microcontractions with different funnel characteristics is presented. The Micro Particle Image Velocimetry technique has been applied to validate the numerical simulations. We demonstrate the use of microfluidics in the reproduction of a large range of controllable extensional strains that can be used in the study of the effect of flow on biological fluids.

Mixing characterisation for a serpentine microchannel equipped with embedded barriers

This paper describes the design, simulation, fabrication and experimental analysis of a passive micromixer for the mixing of biological solvents. The mixer consists of a T-junction, followed by a serpentine microchannel. the serpentine has three arcs, each equipped with circular barriers that are patterned as two opposing triangles. >The barriers are engineered to induce periodic perturbations in the flow field and enhance the mixing. CFD (Computational Fluid Dynamics) method is applied to optimise the geometric variables of the mixer before fabrication. The mixer is made from PDMS (Polydimethylsiloxane) using photo- and soft-lithography techniques. Experimental measurements are performed using yellow and blue food dyes as the mixing fluids. The mixing is measured by analysing the composition of the flow's colour across the outlet channel. The performance of the mixer is examined in a wide range of flow rates from 0.5 to 10 µl/min. Mixing efficiencies of higher than 99.4% are obtained in the experiments confirming the results of numerical simulations. The proposed mixer can be employed as a part of lab-on-a-chip for biomedical applications.

Dielectrophoretic-activated cell sorter based on curved microelectrodes

This article presents the numerical and experimental analysis of a dielectrophoretic-activated cell sorter (DACS), which is equipped with curved microelectrodes. Curved microelectrodes offer unique advantages, since they create strong dielectrophoretic (DEP) forces over the tips and maintain it over a large portion of their structure, as predicted by simulations. The performance of the system is assessed using yeast (Saccharomyces cerevisiae) cells as model organisms. The separation of the live and dead cells is demonstrated at different medium conductivities of 0.001 and 0.14 S/m, and the sorting performance was assessed using a second array of microelectrodes patterned downstream the microchannel. Further, microscopic cell counting analysis reveals that a single pass through the system yields a separating efficiency of ~80% at low medium conductivities and ~85% at high medium conductivities.

Dielectrophoretically assembled particles : feasibility for optofluidic systems

This work presents the dielectrophoretic manipulation of sub-micron particles suspended in water and the investigation of their optical responses using a microfluidic system. The particles are made of silica and have different diameters of 600, 450, and 250 nm. Experiments show a very interesting feature of the curved microelectrodes, in which the particles are pushed toward or away from the microchannel centerline depending on their levitation heights, which is further analyzed by numerical simulations. In doing so, applying an AC signal of 12 V_p-p and 5 MHz across the microelectrodes along with a flow rate of 1 μl/min within the microchannel leads to the formation of a tunable band of particles along the centerline. Experiments show that the 250 nm particles guide the longitudinal light along the microchannel due to their small scattering. This arrangement is employed to study the feasibility of developing an optofluidic system, which can be potentially used for the formation of particles-core/liquid-cladding optical waveguides.