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

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