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ABSTRACT: Many analytical microsystems use molecular diffusion to mix small quantities of different liquids. However, this passive mixing process requires a relatively long microchannel which may impose design restrictions on the physical dimensions of the fluidic network. To shorten the length of the mixing channels, an active micromixer driven by a focused laser beam is described in this paper. The proposed solution improves the mixing rate by using low power laser radiation to heat the disparate fluids being transported through the channels. The operating principle is ba sed on the observation that the rate of molecular diffusion for non-reactive fluids increases with elevated temperatures. Preliminary experiments on a Y-channel micromixer were conducted using a 1mW, 670nm laser. The laser beam was focused on the microchannel using a 100mm focal length objective lens. The laser-assisted mixing of the test fluids showed a 36.4% increase in the average diffusion coefficient value with 1 to 10μL/min flow rates. The maximum percentage difference of diffusion distances had increased by approximately 7.85% over the non-laser-assisted conditions.
Optomechatronic Technologies (ISOT), 2010 International Symposium on; 11/2010
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ABSTRACT: A low cost manufacturing method for creating polymer microfluidic devices with microfeatures that have near optical surface quality is described in this paper. The manufacturing method involves laser micromachining, partial hot embossing, and molding (LHEM) to create polymethylmethacrylate (PMMA) mold masters for device replication. A metallic hot intrusion mask with the desired microfeatures is first machined by laser and then used to produce the mold master by pressing the mask onto a PMMA substrate under applied heat and pressure. The resultant 3D micro-reliefs have near optical quality surface finishes. Design parameters such as the height and width of the extruded features are investigated in this study. The experimental results demonstrate that different heights of the extruded features of a mold master can be fabricated using a single mask at a set of process parameters. Examples of curved microchannels of the PMMA mold masters and an integrated microchannel/microlens of the mold master are presented to illustrate the proposed methodology.
Microsystems and Nanoelectronics Research Conference, 2008. MNRC 2008. 1st; 11/2008
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ABSTRACT: This paper presents a new method for rapid fabrication of polymeric micromold masters for the manufacture of polymer microfluidic devices. The manufacturing method involves laser micromachining of the desired structure of microfluidic channels in a thin metallic sheet and then hot embossing the channel structure onto poly(methyl methacrylate) PMMA substrate to form the mold master. The channeled layer of the microfluidic device is then produced by pouring the polydimethylsiloxane (PDMS) elastomer over the mold and curing it. The method is referred to as LHEM (laser micromachining, hot embossing and molding). Polymers like PDMS are preferred over silicon as the material for building microfluidic devices because of their biocompatibility properties as well as because of their lower cost. The proposed manufacturing method involves fewer processing steps than the conventional soft lithography process and enables manufacture of non-rectangular channels in microfluidic devices. To test the method, a mold for a micro capillary electrophoresis microfluidic chip was fabricated. The experimental results confirmed that high quality (Ra 10 to 100 nm) molds can be fabricated quickly and inexpensively. Advantages and limitations of the proposed method are discussed in the concluding section of the paper.
Journal of Micromechanics and Microengineering 01/2008; 18(2):025012. · 2.11 Impact Factor
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ABSTRACT: Lab-on-a-chip (LOC) and other microfluidic devices for medical applications need to be mass produced at a low fabrication cost because the disposable device is destroyed after a single use to avoid sample contamination. In this paper, a new method for rapidly fabricating metallic micromold masters for manufacturing large volumes of polymeric microfluidic devices is presented. Polymers are preferred over silicon as the device material due to their better compatibility with biological and chemical substances. The manufacturing method involves laser micromachining of the desired imprint features from thin metallic sheets and then microwelding them onto a substrate to form the final mold master. The polydimethylsiloxane (PDMS) elastomer is then poured over the mold and cured to produce the microfluidic device. The proposed method involves fewer processing steps than the soft lithography, electroplating and molding (LIGA) process. To verify the method, a metallic mold for a passive Y-channel microfluidic mixer was fabricated. The mold master was made from low-cost steel and the mold manufacturing process can be completed within an hour. PDMS elastomer is then poured over the mold and cured to produce the mixer. The channels of the mixer were 75 micrometers wide and 50 micrometers high. The mixer created from the mold was tested by mixing two streams of colored water in it. The maximum flow rate achieved by the prototype was 6.4 microlitres per minute. The experimental results confirm that a viable metallic mold master for microfluidic devices can be created by combining laser micromachining and microwelding processes. Finally, the limitations of the proposed rapid fabrication method are discussed.
Electrical and Computer Engineering, 2007. CCECE 2007. Canadian Conference on; 05/2007
