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Highly parallelized biochemical analysis is a significant step toward achieving high throughput processing of patient samples for diagnosis and treatment monitoring. The standard microtiter plate is used to carry out multiple reactions for high throughput screening. By incorporating polymer microfluidic devices at each well in the microtiter plate format, the capability of the format could be significantly enhanced for high throughput processing of large numbers of biochemical samples in a cost-effective manner. Low cost replication of the microtiter plates is done using micro molding techniques, so microfabrication technology for making large area mold inserts (LAMIs) containing microfluidic devices at each well of a microtiter plate format is needed. A large area mold insert (LAMI) in the footprint of the standard microtiter plate was fabricated using an SU-8 based UV-LIGA technique. Excellent lithography results, with vertical sidewalls, were obtained by utilizing flycutting to minimize SU-8 film thickness variation and a UV filter for attenuating high absorbance UV wavelengths. Overplating of nickel in the SU-8 polymeric molds was used to make high quality metallic mold inserts with vertical sidewalls. 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 yielded good sealing results and the developed polymer microfluidic platforms showed good fluidic uniformity.Copyright © 2006 by ASME

Simulations and experiments to assess the predictability of dimensional and locational tolerances of passive alignment structures on injection molded microfluidic components were performed. A center-gated disk with microscale assembly features, to aid metrology, was reproduced using injection molding. The feature dimensions were 100, 200, 300, and 400 μ. Dimensions of the features were measured using optical profilometery and optical microscopy. Simulations using a commercial package overestimated replication fidelity. Mold surface temperatures and injection speeds significantly affected the replication fidelity as the ratio of surface area to volume increased. The location of better replication fidelity, at each mold surface temperature, moved from the edge of the mold cavity to the injection point as the mold surface temperature increased from 100°C to 150°C. Therefore, process parameters and the design of a mold have to be considered for successful replication of the features.Copyright © 2006 by ASME

For connecting polymeric, modular microfluidic devices, precise, passive alignment structures can prevent infinitesimal motions between the devices and minimize misalignment of the devices. The motion and constraint of passive alignment structures were analyzed for the design of assembly features using screw theory. A combination of three v-groove and sphere joints constrained all degrees of freedom of the two mating plates without over-constraint. To validate the designed passive alignment scheme, hot embossing experiments were conducted using a micromilled brass mold insert, containing alignment features. Prototype alignment structures have dimensional variation. The alignment accuracy of the stacked polymeric plates was estimated by the mismatches between alignment marks of two plates. The mismatches ranged from 28 μm to 70 μm.Copyright © 2006 by ASME