18 research outputs found
Stopping microfluidic flow
We present a cross-comparison of three stop-flow configurations--such as
low-pressure (LSF), high-pressure open-circuit (OC-HSF), and high-pressure
short-circuit (SC-HSF) stop-flow--to rapidly bring a high flow velocity within
a microchannel to a standstill. The average velocities inside the microchannels
were reduced from > 1 m/s to < 10 um/s within 2s of initiating the stop-flow.
The performance of the three stop-flow configurations was assessed by measuring
the residual flow velocities within microchannels having three
orders-of-magnitude different flow resistances. The LSF configuration
outperformed the OC-HSF and SC-HSF configurations within the high flow
resistance microchannel, and resulted in a residual velocity of < 10 um/s. The
OC-HSF configuration resulted in a residual velocity of < 150 um/s within a low
flow resistance microchannel. The SC-HSF configuration resulted in a residual
velocity of < 200 um/s across the three orders-of-magnitude different flow
resistance microchannels, and < 100 um/s for the low flow resistance channel.
We hypothesized that the residual velocity resulted from the compliance in the
fluidic circuit, which was further investigated by varying the elasticity of
the microchannel walls and the connecting tubing. A numerical model was
developed to estimate the expanded volumes of the compliant microchannel and
connecting tubings under a pressure gradient and to calculate the distance
traveled by the sample fluid. A comparison of the numerically and
experimentally obtained traveling distances confirmed our hypothesis that the
residual velocities were an outcome of the compliance in the fluidic circuit.
Therefore, a configuration where the fluidic circuit compliance was minimal
resulted in the least residual velocity
Travelling Surface Acoustic Waves Microfluidics
AbstractIn this paper, we demonstrate the working principle of travelling surface acoustic waves (TSAWs) in a microfluidic system. The TSAWs were incorporated to separate polystyrene (PS) particles of variable diameters and perform controlled mixing of different chemicals for concentration gradient generation, both inside a polydimethylsiloxane (PDMS) microfluidic channel. The TSAWs generated an acoustic streaming flow (ASF) upon coupling with a liquid and exerted an acoustic radiation force (ARF) on the suspended particles. The ARF was theoretically estimated for PS microspheres suspended in water, and conditions for ARF dominance over ASF or vice versa were identified. Recently reported TSAW-based PS particles separation and gradient generation results by our group are summarized here
Microparticle self-assembly induced by travelling surface acoustic waves
International audienceWe present an acoustofluidic method based on travelling surface acoustic waves (TSAWs) to induce self-assembly of microparticles inside a microfluidic channel. The particles are trapped above an interdigitated transducer, placed directly beneath the microchannel, by the TSAW-based direct acoustic radiation force (ARF). This approach was applied to trap 10 mm polystyrene particles, which were pushed towards the ceiling of the microchannel by 72 MHz TSAWs to form single-and multiple-layer colloidal structures. The repair of cracks and defects within the crystal lattice occurs as part of the self-assembly process. The sample flow through the first inlet can be switched with a buffer flow through the second inlet to control the number of particles assembled in the crystalline structure. The constant flow-induced Stokes drag force on the particles is balanced by the opposing TSAW-based ARF. This force balance is essential for the acoustics-based self-assembly of microparticles inside the microchannel. Moreover, we studied the effects of varying input voltage and fluid flow rate on the position and shape of the colloidal structure. The active self-assembly of microparticles into crystals with multiple layers can be used in the bottom-up fabrication of colloidal structures with dimensions greater than 500 mm  500 mm, which is expected to have important applications in various fields
Sheathless Focusing and Separation of Microparticles Using Tilted-Angle Traveling Surface Acoustic Waves
Sheathless focusing
and separation of microparticles is an important
preprocessing step in various biochemical assays in which enriched
sample isolation is critical. Most of the previous microfluidic particle
separation techniques have used sheath flows to achieve efficient
sample focusing. The sheath
flow dilutes the analyte and requires additional microchannels and
accurate flow control. We demonstrated a tilted-angle traveling surface
acoustic wave (taTSAW)-based sheathless focusing and separation of
particles in a continuous flow. The proposed device consists of a
piezoelectric substrate with a pair of interdigitated transducers
(IDTs) deposited at two different angles relative to the flow direction.
A Y-shaped polydimethylsiloxane (PDMS) microchannel having one inlet
and two outlet ports was positioned on top of the IDTs such that the
acoustic energy coupling into the fluid was maximized and wave attenuation
by the PDMS walls was minimized. The two IDTs independently produced
high-frequency taTSAWs, which propagated at ±30° with respect
to the flow direction and imparted a direct acoustic radiation force
onto the target particles. A sample mixture of 4.8 and 3.2 μm
particles was focused and then separated by the actuation of the IDTs
at 194 and 136 MHz frequencies, respectively, without using an additional
sheath flow. The proposed taTSAW-based particle separation device
offered a high purity >99% at the both outlets over a wide range
of
flow speeds (up to 83.3 mm/s)
Transfer of Microparticles across Laminar Streams from Non-Newtonian to Newtonian Fluid
Engineering inertial lift forces
and elastic lift forces is explored
to transfer microparticles across laminar streams from non-Newtonian
to Newtonian fluid. A co-stream of non-Newtonian flow loaded with
microparticles (9.9 and 2.0 μm in diameter) and a Newtonian
carrier medium flow in a straight rectangular conduit is devised.
The elastic lift forces present in the non-Newtonian fluid, undeterred
by particle–particle interaction, successfully pass most of
the larger (9.9 μm) particles over to the Newtonian fluid. The
Newtonian fluid takes over the larger particles and focus them on
the equilibrium position, separating the larger particles from the
smaller particles. This mechanism enabled processing of densely suspended
particle samples. The method offers dilution-free (for number densities
up to 10 000 μL<sup>–1</sup>), high throughput
(6700 beads/s), and highly efficient (>99% recovery rate, >97%
purity)
particle separation operated over a wide range of flow rate (2 orders
of magnitude)
Particle Separation inside a Sessile Droplet with Variable Contact Angle Using Surface Acoustic Waves
A sessile
droplet of water carrying polystyrene microparticles
of different diameters was uniformly exposed to high frequency surface
acoustic waves (SAWs) produced by an interdigitated transducer (IDT).
We investigated the concentration behavior of the microparticles as
the SAWs generated a strong acoustic streaming flow (ASF) inside the
water droplet and exerted a direct acoustic radiation force (ARF)
on the suspended particles, the magnitude of which depended upon the
particle diameter. As a result of the ARF, the microparticles were
concentrated according to their diameters at different positions inside
the sessile droplet placed in the path of the SAW, right in front
of the IDT. The microparticle concentration behavior changed as the
sessile droplet contact angle with the substrate was varied by adding
surfactant to the water or by gradually evaporating the water. The
positions at which the smaller and larger microparticles were concentrated
remained distinguishable, even at very different experimental conditions.
The long-term exposure of the droplets to the SAWs was accompanied
by the gradual evaporation of the carrier fluid, which dynamically
changed the droplet contact angle as well as the concentration of
particles. Complete evaporation of the fluid left behind several concentrated
yet separated clusters of particles on the substrate surface. The
effect of the droplet contact angle on particles’ concentration
behavior and consequent separation of particles has been uniquely
studied in this SAW-based report
Particle Separation inside a Sessile Droplet with Variable Contact Angle Using Surface Acoustic Waves
A sessile
droplet of water carrying polystyrene microparticles
of different diameters was uniformly exposed to high frequency surface
acoustic waves (SAWs) produced by an interdigitated transducer (IDT).
We investigated the concentration behavior of the microparticles as
the SAWs generated a strong acoustic streaming flow (ASF) inside the
water droplet and exerted a direct acoustic radiation force (ARF)
on the suspended particles, the magnitude of which depended upon the
particle diameter. As a result of the ARF, the microparticles were
concentrated according to their diameters at different positions inside
the sessile droplet placed in the path of the SAW, right in front
of the IDT. The microparticle concentration behavior changed as the
sessile droplet contact angle with the substrate was varied by adding
surfactant to the water or by gradually evaporating the water. The
positions at which the smaller and larger microparticles were concentrated
remained distinguishable, even at very different experimental conditions.
The long-term exposure of the droplets to the SAWs was accompanied
by the gradual evaporation of the carrier fluid, which dynamically
changed the droplet contact angle as well as the concentration of
particles. Complete evaporation of the fluid left behind several concentrated
yet separated clusters of particles on the substrate surface. The
effect of the droplet contact angle on particles’ concentration
behavior and consequent separation of particles has been uniquely
studied in this SAW-based report
Generation of Dynamic Free-Form Temperature Gradients in a Disposable Microchip
Temperature
gradients (TGs) provide an effective approach to controlling
solvated molecules and creating spatiotemporally varying thermal stimuli
for biochemical research. Methods developed to date for generating
TGs can only create a limited set of static temperature profiles.
This article describes a method for establishing dynamic free-form
TGs in polydimethylsiloxane (PDMS) as well as in gases and liquids
in contact with the PDMS. The heating mechanism relies on the efficient
acoustic absorption by the PDMS of high-frequency (5–200 MHz)
surface acoustic waves (SAWs). MATLAB-aided actuation of a transducer
enabled the generation and propagation of SAWs in a controlled fashion,
which permitted spatiotemporal control over the temperature in the
PDMS microstructures. This technique is exploited to perform one-shot
high-resolution melting (HRM) analysis to detect single nucleotide
polymorphisms (SNPs) in DNA. The experimental results displayed a
10-fold higher resolution and an enhanced signal-to-noise ratio compared
to the results obtained using a conventional real-time PCR machine