Microfluidic technology has the potential to revolutionise blood-clotting diagnostics by incorporating key physiological blood flow conditions like shear rate. In this paper we present a customised dynamic microfluidic system, which evaluates the blood clotting response to multiple conditions of shear rate on a single microchannel. The system can achieve high-throughput testing through use of an advanced fluid control system, which provides with rapid and precise regulation of the blood flow conditions in the platform. We present experimental results that demonstrate the potential of this platform to develop into a high-throughput, low-cost, blood-clotting diagnostics device.
Microfluidic platforms have been widely considered as an enabling technology for studying the ion transport phenomena
of cells under precisely controlled shear stresses. Here, we report the application of a unique microfluidic platform to
analyze the response of transgenic TRPV4-HEK293 cells in response to different shear stresses and in one field of view.
Applying this system, we show the kinetics of calcium signalling at different shear stresses in TRPV4 positive cells and
elucidate the threshold of their response. We show that there is direct correlation between the magnitude of shear stress
and percentage of cells that are able to sense that level of shear. Further, we show that shear stress-induced elevation in
intracellular calcium levels ([Ca<sup>2+</sup>]i) is through calcium influx from extracellular sources. The results demonstrate that the microfluidic system has unique capabilities for analysis of shear stress on adhesive cells and that it should be amenable to moderate throughput applications.
Dielectrophoresis, the induced motion of polarisable particles in non-homogenous electric field, has been proven
as a versatile mechanism to transport, immobilise, sort and characterise micro/nano scale particle in microfluidic
platforms. The performance of dielectrophoretic (DEP) systems depend on two parameters: the configuration of
microelectrodes designed to produce the DEP force and the operating strategies devised to employ this force in
such processes. This work summarises the unique features of curved microelectrodes for the DEP manipulation
of target particles in microfluidic systems. The curved microelectrodes demonstrate exceptional capabilities
including (i) creating strong electric fields over a large portion of their structure, (ii) minimising electro-thermal
vortices and undesired disturbances at their tips, (iii) covering the entire width of the microchannel influencing
all passing particles, and (iv) providing a large trapping area at their entrance region, as evidenced by extensive
numerical and experimental analyses. These microelectrodes have been successfully applied for a variety of
engineering and biomedical applications including (i) sorting and trapping model polystyrene particles based on
their dimensions, (ii) patterning carbon nanotubes to trap low-conductive particles, (iii) sorting live and dead
cells based on their dielectric properties, (iv) real-time analysis of drug-induced cell death, and (v) interfacing
tumour cells with environmental scanning electron microscopy to study their morphological properties. The
DEP systems based on curved microelectrodes have a great potential to be integrated with the future lab-on-achip
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.
Microfluidics has the potential to enhance the understanding of the of biological fluids under strain, due to the
laminar nature of the fluid and the possibility to mimic the real conditions. We present advances on characterization
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 siloxane
(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.
Biological fluids such as blood, proteins and DNA solutions moving within fluidic channels can potentially be
exposed to high level of shear, extension or mixed stress, either in vitro such as industrial processing of blood
products or in vivo such as ocurrs in some pathological conditions. This exposure to a high level of strain can
trigger some reactions. In most of the cases the nature of the flow is mixed with shear and extensional components.
The ability to isolate the effects of each component is critical in order to understand the mechanisms behind the
reactions and potentially prevent them. Applying hydrodynamic flow focusing, we present in this investigation
the characterization of microchannels that allow study of the regions of high shear or high extension strain rate.
Micro channels were fabricated in polydimethyl siloxane (PDMS) using standard soft-lithography techniques
with a photolithographically patterned mold. Characterization of the regions with high shear and high extension
strain rate is presented. Computational Fluid Dynamics (CFD) simulations in three dimensions have been
carried out to gain more detailed local flow information, and the results have been validated experimentally. A
comparison between the numerical models and experiment and is presented. The advantages of microfluidic flow
focusing in the study of the effects of shear and extension strain rates for biological fluids are outlined.
Protein aggregation is arguably the most common and troubling manifestation of protein instability, encountered in
almost all stages of protein drug development. The production process in the pharmaceutical industry can induce flows
with shear and extensional components and high strain rates which can affect the stability of proteins. We use a
microfluidic platform to produce accurately controlled strain regions in order to systematically study the main
parameters of the flow involved in the protein aggregation. This work presents a characterization of the pressure driven
flow encountered in arrays of micro channels. The micro channels were fabricated in polydimethyl siloxane (PDMS)
using standard soft-lithography techniques with a photolithographically patterned KMPR mold. We present a
relationship of the main geometrical variables of the micro channels and its impact on the extensional strain rate along
the center line, for different cross sectional shapes and over a range of strain rates typically encountered in protein
processing. Computational Fluid Dynamics (CFD) simulations have been carried out to gain more detailed local flow
information, and the results have been validated with experiments. We show good agreement between the CFD and
experiments and demonstrate the use of microfluidics in the production of a large range of controllable shear and
extensional rates that can mimic large scale processing conditions.