Three-dimensional Flow Focusing Research Articles

Structural Formation of Oil-in-Water (O/W) and Water-in-Oil-in-Water (W/O/W) Droplets in PDMS Device Using Protrusion Channel without Hydrophilic Surface Treatment.

This paper presents a simple method of droplet formation using liquids that easily wet polydimethylsiloxane (PDMS) surfaces without any surface treatment. Using only structural features and uniform flow focusing, Oil-in-Water (O/W) and Water-in-Oil-in-Water (W/O/W) droplets were formed in the full PDMS structure. Extrusion channel and three-dimensional flow focusing resulted in effective fluidic conditions for droplet formation and the droplet size could be precisely controlled by controlling the flow rate of each phase. The proposed structure can be utilized as an important element for droplet based research, as well as a droplet generator.

A Three-Dimensional Flow Focusing Microsecond Mixer for Dynamic Assessment of Nanoparticle Formation

This paper reports the design, fabrication, and characterization of a three-dimensional flow focusing microfluidic mixer. By hydrodynamically focusing the sample stream into a very confined jet in both vertical and horizontal directions, the mixer can achieve ultrafast mixing of reagents within ∼3 ± 1 μs. Such rapid mixing allows us to dynamically assess the formation of nanomaterial and study their assembly kinetics on microsecond timescale. Using the mixer, we investigated the formation of the hexaphenylsilole (HPS) nanoparticles. Compared to those formed by bulk nanoprecipitation, the HPS nanoparticles formed in the mixer have smaller size with narrower size distribution. We also kinetically resolved that the microsecond molecular self-assembly of HPS molecules displays two distinct steps. These results suggest that the formation of HPS nanoparticles follows the classical nucleation and growth theory.

Glass capillary microfluidics for production of monodispersed poly (dl-lactic acid) and polycaprolactone microparticles: Experiments and numerical simulations

HypothesisDroplet size in microfluidic devices is affected by wettability of the microfluidic channels. Three-dimensional countercurrent flow focusing using assemblies of chemically inert glass capillaries is expected to minimize wetting of the channel walls by the organic solvent. ExperimentsMonodispersed polycaprolactone and poly(lactic acid) particles with a diameter of 18–150μm were produced by evaporation of solvent (dichloromethane or 1:2 mixture of chloroform and toluene) from oil-in-water or water-in-oil-in-water emulsions produced in three-dimensional flow focusing glass capillary devices. The drop generation behaviour was simulated numerically using the volume of fluid method. FindingsThe numerical results showed good agreement with high-speed video recordings. Monodispersed droplets were produced in the dripping regime when the ratio of the continuous phase flow rate to dispersed phase flow rate was 5–20 and the Weber number of the dispersed phase was less than 0.01. The porosity of polycaprolactone particles increased from 8 to 62% when 30wt% of the water phase was incorporated in the organic phase prior to emulsification. The inner water phase was loaded with 0.156wt% lidocaine hydrochloride to achieve a sustained drug release. 26% of lidocaine was released after 1h and more than 93% of the drug was released after 130h.

Universally applicable three-dimensional hydrodynamic microfluidic flow focusing

We have demonstrated a microfluidic device that can not only achieve three-dimensional flow focusing but also confine particles to the center stream along the channel. The device has a sample channel of smaller height and two sheath flow channels of greater height, merged into the downstream main channel where 3D focusing effects occur. We have demonstrated that both beads and cells in our device display significantly lower CVs in velocity and position distributions as well as reduced probability of coincidental events than they do in conventional 2D-confined microfluidic channels. The improved particle confinement in the microfluidic channel is highly desirable for microfluidic flow cytometers and in fluorescence-activated cell sorting (FACS). We have also reported a novel method to measure the velocity of each individual particle in the microfluidic channel. The method is compatible with the flow cytometer setup and requires no sophisticated visualization equipment. The principles and methods of device design and characterization can be applicable to many types of microfluidic systems.

Ultrafast microfluidic mixer with three-dimensional flow focusing for studies of biochemical kinetics

Studies of the kinetics of biochemical reactions, especially of folding of proteins and RNA, are important for understanding the function of biomolecules and processes in live cells. Many biochemical reactions occur rapidly and thus need to be triggered on very short time scales for their kinetics to be studied, which is often accomplished by mixing in a turbulent flow. More rapid and sample-efficient mixing is achieved in laminar flow in a microfluidic device, in which the sample is two-dimensionally (2D) focused to a thin sheet. Here we describe the design and operation of an ultrafast microfluidic mixer with three-dimensional (3D) flow focusing. The confinement of a 3D-focused sample to a narrow stream near the middle of a microchannel renders its velocity nearly uniform and makes it possible to monitor the reaction kinetics without exclusion of any parts of the sample. Hence, the sample consumption is substantially reduced and the fluorescence of the sample can be monitored without a confocal setup. Moreover, the 3D-focusing allows facile measurements of velocity of the sample with a high spatial resolution using a specially developed technique based on epi-fluorescence imaging. The data on the velocity vs. position are used to precisely calibrate the conversion between position and the reaction time, which is essential for accurate kinetic measurements. The device performs mixing on a 10 micros scale, which is comparable to that of the laminar mixers with 2D focusing. Unlike previous ultrafast laminar mixers, which were machined in hard materials, the present microfluidic device is made of a single cast of poly(dimethylsiloxane), PDMS, and is thus simpler and less expensive to manufacture.

Investigations of micrometer sample stream profiles in a three-dimensional hydrodynamic focusing device

Abstract In this work we describe the design and fabrication of a novel three-dimensional flow focusing device with channel dimensions of 50 μm × 50 μm at the focusing region. The device is suitable for one-by-one cell or particle detection near the channel bottom, in for example a Coulter counter or for optical near field detection. The device comprises a silicon-glass sandwich with SU-8 resist in between. The sample flow is hydrodynamically focused between three sheath flows. At the fourth side the sample flow is moving along the channel bottom. We investigated the focusing limitation of the sample flow and found that the minimum width amounts to 2.5 μm at a channel width of 50 μm. Confocal laser scanning measurements were constituted to obtain the sample flow profile. We show the experimental and numerical images of the focused stream shape from a cross-section perspective. Furthermore, we analyzed the measured fluorescent color intensity of the sample stream and from that, calculated the sample flow height. These results were compared with the corresponding confocal images. Additionally, the influence of the hydrodynamic focusing on the sample profile and its uniformity over a certain distance was investigated.