Microassembly technology for modular, polymer microfluidic devices
Assembly of modular, polymer microfluidic devices with different functions to obtain more capable instruments may significantly expand the options available for detection and diagnosis of disease through DNA analysis and proteomics. For connecting modular devices, precise, passive alignment structures can be used to prevent infinitesimal motions between the devices and minimize misalignment. The motion and constraint of passive alignment structures were analyzed using screw theory. A combination of three v-groove and hemisphere-tipped post joints constrained all degrees of freedom of the two mating modules without overconstraint. Simulations and experiments were performed to assess the predictability of dimensional and location variations of injection molded components. A center-gated disk with micro scale assembly features was replicated. Simulations using a commercial package (Moldflow) overestimated replication fidelity. Mold surface temperatures and injection speeds significantly affected the experimental replication fidelity. The location of features for better replication, 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. Prototype modular devices were replicated using double-sided injection molding for the experimental demonstration. Dimensional and location variations of the assembly features and alignment standards were quantified for an assembly tolerance analysis. Monte Carlo methods were applied to the assembly tolerance analysis to simulate propagation and accumulation of variation in the assembly. In simulations, mean mismatches with standard deviations ranged from 115±29 to 118±30 µm and from 17±11 to 19±13 µm along the X- and Y-axes, respectively. Vertical gaps with standard deviations at the X- and Y-axes were 312±37~319±37 µm, compared to the designed value of 287µm. The measured lateral mismatches were 103±7~116±11 µm and 15±9~20±6 µm along the X- and Y-axes, respectively. The vertical gaps ranged from 277±4 µm to 321±7 µm at the X- and Y-axes, respectively. The present study combined an investigation of microassembly technology with a better understanding of the micro injection molding process, to assist in realizing cost-effective mass production of modular, polymer microfluidic devices enabling biochemical analysis.
Underconstraint, Micro Injection Molding, Overconstraint, Passive Alignment, Assembly Tolerance Analysis, Monte Carlo Simulation
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