A tunable microflow focusing device utilizing controllable moving walls and its applications for formation of micro-droplets in liquids

This study reports a new microfluidic device capable of fine-tuned sample-flow focusing and generation of micro-droplets in liquids by controlling moving wall structures. Two microfluidic components including an 'active microchannel width controller' and a 'micro chopper' can be used to fine-tune the width of the hydrodynamically pre-focused stream and subsequently generate micro-droplets. In this study, a basic concept of a 'controllable moving wall' structure was addressed and applied as the active microchannel width controller and the micro chopper to generate the proposed function. Pneumatic side chambers were placed next to a main flow channel to construct the controllable moving wall structures. The deformation of the controllable moving wall structure can be generated by the pressurized air injected into the pneumatic side chambers. The proposed chip device was fabricated utilizing polymer material such as PDMS (polydimethylsiloxane) to provide the flexibility of the controllable moving wall deformation. The microfluidic chip device with dimensions of 2.5 cm in width and 3.0 cm in length can be fabricated using a simple fabrication process. Experimental data showed that the deformation of the controllable moving wall structure can be adjusted by applying different air pressures, so that the width of the main flow channel can be controlled accordingly. By utilizing the proposed mechanism, the pre-focused dispersed phase stream could be actively focused into a narrower stream, and well-controlled micro-droplets with smaller diameters could be generated. The stream width can be reduced from 30 µm to 9 µm and micro-droplets with a diameter of 76 µm could be generated by utilizing the proposed device. In addition, to generate micro-droplets within smaller diameters, uniform size distribution of the micro-droplets can be obtained. According to the experimental results, development of the microfluidic device could be promising for a variety of applications such as emulsification, nano-medicine and droplet-based microfluidics.

[1]  Minoru Seki,et al.  Characterization of Spontaneous Transformation-Based Droplet Formation during Microchannel Emulsification , 2002 .

[2]  B. Bhandari,et al.  Nano-Emulsion Production by Sonication and Microfluidization—A Comparison , 2006 .

[3]  H. Stone,et al.  Formation of dispersions using “flow focusing” in microchannels , 2003 .

[4]  Magalie Faivre,et al.  Microfluidic flow focusing: Drop size and scaling in pressure versus flow‐rate‐driven pumping , 2005, Electrophoresis.

[5]  George M. Whitesides,et al.  Formation of monodisperse bubbles in a microfluidic flow-focusing device , 2004 .

[6]  Goran T. Vladisavljevic,et al.  Preparation and analysis of oil-in-water emulsions with a narrow droplet size distribution using Shirasu-porous-glass (SPG) membranes☆ , 2002 .

[7]  S. Sugiura,et al.  Preparation Characteristics of Monodispersed Water-in-Oil Emulsions Using Microchannel Emulsification , 2001 .

[8]  L. Rayleigh.  On The Instability Of Jets , 1878 .

[9]  Gwo-Bin Lee,et al.  Formation of Microdroplets in Liquids Utilizing Active Pneumatic Choppers on a Microfluidic Chip , 2006, Journal of Microelectromechanical Systems.

[10]  Minoru Seki,et al.  Effect of Channel Structure on Microchannel Emulsification , 2002 .

[11]  Sebastián Chávez,et al.  Flow Focusing: a versatile technology to produce size-controlled and specific-morphology microparticles. , 2005, Small.

[12]  Flow focusing in microchannels , 2005 .

[13]  Gwo-Bin Lee,et al.  Micro-droplet formation utilizing microfluidic flow focusing and controllable moving-wall chopping techniques , 2006 .

[14]  Levent Yobas,et al.  High-performance flow-focusing geometry for spontaneous generation of monodispersed droplets. , 2006, Lab on a chip.

[15]  H. Schubert,et al.  Production of emulsions using microporous, ceramic membranes , 1999 .

[16]  Toshiro Higuchi,et al.  Droplet formation in a microchannel network. , 2002, Lab on a chip.

[17]  Krassimir D. Danov,et al.  Capillary mechanisms in membrane emulsification: oil-in-water emulsions stabilized by Tween 20 and milk proteins , 2002 .

[18]  Alex Groisman,et al.  Two-dimensional hydrodynamic focusing in a simple microfluidic device , 2005 .

[19]  Yuji Kikuchi,et al.  Production of Oil-in-Water Microspheres Using a Stainless Steel Microchannel. , 2001, Journal of colloid and interface science.

[20]  Vittorio Cristini,et al.  Monodispersed microfluidic droplet generation by shear focusing microfluidic device , 2006 .

[21]  R. V. D. Sman,et al.  Analysis of droplet formation and interactions during cross-flow membrane emulsification , 2002 .