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

Tunable Picoliter-Scale Dropicle Formation Using Amphiphilic Microparticles with Patterned Hydrophilic Patches.

Microparticle-templated droplets or dropicles have recently gained interest in the fields of diagnostic immunoassays, single-cell analysis, and digital molecular biology. Amphiphilic particles have been shown to spontaneously capture aqueous droplets within their cavities upon mixing with an immiscible oil phase, where each particle templates a single droplet. Here, an amphiphilic microparticle with four discrete hydrophilic patches embedded at the inner corners of a square-shaped hydrophobic outer ring of the particle (4C particle) is fabricated. Three dimensional computational fluid dynamics simulations predict droplet formation dynamics and differing equilibrium conditions depending on the patterning configuration. Experiments recapitulate equilibrium conditions, enabling tunable dropicle configurations with reproducible volumes down to ≈200 pL templated by the amphiphilic particles. The dropicle configurations depend predominantly on the size of the hydrophilic patches of the 4C particles. This validates that the modeling approach can inform the design of dropicles with varying volumes and numbers per particle, which can be harnessed in new amplified bioassays for greater sensitivity, dynamic range, and statistical confidence

One‐Way Particle Transport Using Oscillatory Flow in Asymmetric Traps

One challenge of integrating of passive, microparticles manipulation techniques into multifunctional microfluidic devices is coupling the continuous‐flow format of most systems with the often batch‐type operation of particle separation systems. Here, a passive fluidic technique—one‐way particle transport—that can conduct microparticle operations in a closed fluidic circuit is presented. Exploiting pass/capture interactions between microparticles and asymmetric traps, this technique accomplishes a net displacement of particles in an oscillatory flow field. One‐way particle transport is achieved through four kinds of trap–particle interactions: mechanical capture of the particle, asymmetric interactions between the trap and the particle, physical collision of the particle with an obstacle, and lateral shift of the particle into a particle–trapping stream. The critical dimensions for those four conditions are found by numerically solving analytical mass balance equations formulated using the characteristics of the flow field in periodic obstacle arrays. Visual observation of experimental trap–particle dynamics in low Reynolds number flow (<0.01) confirms the validity of the theoretical predictions. This technique can transport hundreds of microparticles across trap rows in only a few fluid oscillations (<500 ms per oscillation) and separate particles by their size differences.Passive fluidic particle transport using asymmetric traps in nonacoustic oscillatory flow is developed. The conditions to achieve this technique are based on the mass balance of fluid flows, the theory of deterministic lateral displacement of microparticles, and experimental validation. This technique can transport or separate microparticles in a closed chamber and facilitate the integration of the microparticle system into portable lab‐on‐a‐chip devices.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/142443/1/smll201702724-sup-0001-S1.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/142443/2/smll201702724.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/142443/3/smll201702724_am.pd

집중적인 표면 진행 탄성파를 이용한 입자 분리 및 화학적 구배 제어

학위논문(석사) - 한국과학기술원 : 기계공학전공, 2013.8, [ vii, 48 p. ]A novel focused travelling surface acoustic waves (F-TSAW) based micro-chip is demonstrated here to continuously separate microparticles, generate chemical gradient, and uniformly mix fluids inside a PDMS mi-crofluidic channel. A pair of curved interdigitated electrodes deposited on a piezoelectric substrate (LiNbO3) produced unidirectional F-TSAW when high frequency AC signal is applied across the terminals of the trans-ducer. F-TSAW, when interacted with the fluid inside the microfluidic channel, imparted acoustic radiation force (ARF) to the suspended microparticles and induced acoustic streaming flow (ASF). ARF is used to sepa-rate the particles whereas ASF generated chemical gradient and uniformly mixed fluids. Previously reported acoustofluidic based particle separators use standing surface acoustic waves (SSAW) whereas chemical gradi-ent generator and micro-mixer depends on acoustic streaming induced by oscillating bubbles. F-TSAW based micro-chip did not require a trapped bubble and a cumbersome microchannel alignment step, which is essential for the working of SSAW particle separator, is also eliminated. All three functions - separation, gradient genera-tion and mixing - are performed on a single micro-chip with performance comparable with already reported devices. After selecting appropriate microchannel (w×h: 200um×40um) and flow rate (100uL/h-1200uL/h or 3.5mm/s-41.67mm/s), variable size polystyrene particles suspended in DI water are successfully separated with power input in excess of 235mW (23.7dBm) and separation efficiency of 100%. ARF separated micropar-ticles with diameter 10um from 3um by inducing an acoustophoretic separation distance whereas effect of ASF is negligible with the aforementioned experimental conditions. The trajectory of separated microparticles is slightly effected by the ASF but it does not affect the separation efficiency. F-TSAW micro-chip harnessed ASF to generate chemical gradient and mix fluids inside a microchannel. ...한국과학기술원 : 기계공학전공

음향파를 이용한 마이크로채널과 정지액적 내 마이크로입자 조작

학위논문(박사) - 한국과학기술원 : 기계공학과, 2018.2,[181 p. :]In this thesis, acoustofluidic platforms have been developed to manipulate microparticles inside a microfluidic channel and a sessile droplet. Acoustofluidic devices utilized for this purpose are based on surface acoustic waves and Lamb waves. Separation of two different sized particles, with diameter difference less than one micrometer, is realized by the high frequency travelling waves. Another travelling waves-based device is further used to demonstrate tri-particle separation where waves originate from two opposite locations of the microchannel and form uniquely observed microchannel anechoic corners within the channel. The acoustofluidic platform is used to perform size-independent separation of particles as well. Similarly, particles manipulation and separation have been demonstrated within sessile droplets. The fundamental principles behind the efficient manipulation of microparticles are the direct acoustic radiation forces by the travelling and standing acoustic waves which are combined with the acoustic streaming flow based drag force to obtain desired results. The dimensions of the fluidic domain carrying the particles are important parameters along with the frequency of the incident waves and the diameter of the particles. Theoretical estimation of the acoustic radiation force provides the necessary framework to choose appropriate experimental conditions for a particular application.한국과학기술원 :기계공학과