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The ligase detection reaction (LDR) is a technique that can distinguish low-abundant mutant DNAs from wild-type DNAs. LDR is usually carried out on DNAs amplified using the polymerase chain reaction (PCR). In the realization of modular microfluidic systems, the DNA output of the PCR handed off to the LDR chip needs to be mixed with LDR reagents before continuing the reaction. Polymer, continuous flow ligase detection reaction (CFLDR) devices with integrated passive micromixers, were designed, fabricated and tested. The devices each consisted of: a passive mixer for mixing a PCR sample, a cocktail of primers, and ligase, an enzyme of DNA; an incubator channel (95°C) for preheating the mixture; and a thermal cycling channel for the LDR. The devices were produced by hot embossing polycarbonate (PC) substrates with brass mold inserts manufactured by micro-milling. Experiments using food dyes showed that the appropriate mixture concentrations were delivered to the preheating channel in both the pulling and pushing modes.Copyright © 2007 by ASME

A highly parallel, polymerase chain reaction (PCR) multireactor platform is in high demand to satisfy the high throughput requirements for exploiting the accumulated genetic information from the Human Genome Project. By incorporating continuous flow PCR (CFPCR) devices in a polymer 96-well titer plate format, DNA amplification can be performed with steady-state temperature control and faster reaction speed at lower cost. Prior to the realization of a PCR multi-reactor platform, consisting of a sample delivery chip, a PCR multireactor chip, and a thermal cycler, optimization of the geometry for CFPCR devices in a titer plate-based PCR multi-reactor chip based on manufacturing feasibility is necessary. A prototype PCR multi-reactor chip was designed in a 96-well titer plate format with twelve different CFPCR configurations. High quality metallic, large area mold inserts (LAMIs) were fabricated using an SU-8 based UV-LIGA technique by overplating nickel in SU-8 electroplating templates. Micro molding of polycarbonate (PC) was done using hot embossing, resulting in good replication fidelity over the large surface area. Thermal fusion bonding of the molded PC chips using a custom-made bonding jig yielded acceptable sealing results. The manufacturability investigation throughout the design and the process sequence suggested that the microchannel walls require a minimum width of at least 20 μm and an aspect ratio of 2 for structural rigidity. An optimal CFPCR device for use in a PCR multi-reactor chip can be selected with a series of amplification experiments with the development of a thermal cycler.

A method of collecting and delivering single or precise numbers of cells to assess the feasibility of capturing very rare circulating tumor cells for human breast cancer diagnosis and monitoring was developed. A PMMA device was assembled with minimal assembly variation using passive alignment. Thermoplastic fusion bonding was optimized to yield minimal deformation of the microfluidic channel. UV modification and an anti-epithelial cell adhesion molecule (anti-EpCAM) functionalization process were used to generate capture surfaces and maximized by control experiment. Single or precise numbers of target cells were collected using a cell collecting capillary tube and a hemacytometer and delivered into the microchannel without any loss. Cells from one of the human breast cancer cell lines, the MCF-7 cell line (ATCC, Manassas, VA) which strongly overexpresses EpCAM, were successfully captured on the anti-EpCAM coated microchannel surfaces. Successful capture of early stage breast cancer cells in whole blood may be feasible with further optimization of the microchannel geometry and flow velocity through the microfluidic device.

BioMEMS are compact devices which use microfabrication to miniaturize conventional benchtop instruments. The benefits of using micro devices are the need for less chemical reagents, faster processing, and portability. Realizing a powerful sample-to-answer micro system requires more than just microfabrication technology; thermal management, microfluidic control, and interfacing technology must also be considered. You et al. [1] applied kinematic constraint analysis using screw theory to design the assembly features for passive alignment structures for polymer, modular microfluidic devices. Three pairs of v-groove and hemispherical pin joints were chosen as kinematic pairs for mating two modules. Dimensional variation of the assembly features was one of principal contributions to the mismatch of 28 μm-75 μm between stacked plates in assembly that was reported. This was primarily a result of incomplete mold filling and deformation of the passive alignment structures during the demolding process. Hemisphere-tipped recesses, with additional annular walls as dummy structures, were used to designed to achieve better replication by improving polymer filling and reducing the deformation during demolding. In prototype devices, the posts with the annular dummy structures had a mean height of 922.2 μm – 924.1 μm while the original posts without dummy structures had mean heights of 865.3 μm – 891.2 μm in 10 samples under the same embossing conditions for a design height of 925 μm. Alignment accuracy of better than 10 μm was achieved in the assembly of two plates.Copyright © 2007 by ASME

An experimental study was conducted to investigate the characteristics of gas-liquid two-phase flow in 200 μm square microchannels thermoformed in polymer chips. Polymer microfluidic chips were replicated using hot embossing of poly(methyl methacrylate) (PMMA) with micromachined brass mold inserts. The thermoformed microchannels in polymer chips typically had greater surface roughnesses compared to microchannels etched in the silicon substrate. Two more different polymer chips, a direct micromachined PMMA chip and a chip hot embossed with a LIGA nickel mold insert, were fabricated to compare surface characteristics of the sidewalls and bottoms of fabricated microchannels. Deionized water and dry air were injected separately into the chips at superficial velocities of jL = 0.005 – 0.11 m/s for the liquid and jG = 0.003 – 16.67 m/s for the gas. Capillary bubbly, plug, plug-annular, annular, and dry flows were observed in the microchannels. Two-phase flow pattern maps and transitions between flow regimes were determined for fixed values of the homogeneous liquid fraction defined as βL = QL /(QL + QG ) where QL and QG are the liquid and gas flow rates, and the liquid Weber number fraction defined as γL = WeL /(WeL + WeG ) where WeL and WeG are the liquid and gas Weber number. The surface roughness in submicron range showed minor effect in comparison with the previous work in terms of the gas-liquid two-phase flow patterns and transitions between flow regimes. Dimensionless bubble sizes scaled by the width of observation microchannel were plotted against the homogeneous liquid fraction (βL ). A scaling law for the bubble length developed for the previous work with T-junctions was applicable to the present work used the cross junction for generation of segmented flow. With a fixed value of the fitting parameter, scaling law showed a good agreement with the experimental data. Deviation of the scaled bubble length from predicted bubble length line and irregularity of bubble length with a fixed homogeneous liquid fraction increased with higher gas flow rates.Copyright © 2007 by ASME