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 ([Ca2+]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
systems.
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.
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