Assembly of Polymer Microfluidic Components and Modules: Validating Models of Passive Alignment Accuracy

Abstract

Low-cost modular polymer microfluidic platforms integrating several different functional units may potentially reduce the cost of molecular and environmental analyses, and enable broader applications. Proper function of such systems depends on well-characterized assembly of the instruments. Passive alignment is one approach to obtaining such assemblies. Model modular devices containing passive alignment features, hemispherical pins in v-grooves, and integrated alignment standards for characterizing the accuracy of the assemblies were replicated in polycarbonate using doubled-sided injection molding. The dimensions and locations of the assembly features and alignment standards were measured. The assemblies had mismatches from 16 ± 4 to 20 ± 6 µm along the x-axis and from 103 ± 7 to 118 ± 11 µm along the y-axis. The vertical variation from the nominal value of 287 µm ranged from −10 ± 4 to 34 ± 7 µm. An assembly tolerance model was used to estimate the accuracy of the assemblies based on the manufacturing variations of the alignment structures. Variation of the alignment structure features were propagated through the assembly using Monte Carlo methods. The estimated distributions matched the measured experimental results well, with differences of 2%-13% due to unmodeled aspects of the variations Accurate assembly of advanced polymer microsystems is feasible and predictable in the design phase.[2014-0125] he is working on microfluidic devices/systems for stroke detection and polymer-based micromodels for flow visualization in artifical porous media. His current research interests include micro/nano fabrication techniques and their applications to bioMEMS, enhanced oil recovery, and micro/nano scale sensors and actuators.

Accurate, predictable, repeatable micro-assembly technology for polymer, microfluidic modules

“…A well-defined toolkit of features, which can be used directly in engineering design, with the twist matrix for each was presented by Whitney et al [48] and Adams and Whitney [49]. You et al showed the feasibility of using polymer passive alignment structures, comprised of three pairs of hemisphere-tipped posts mating with v-grooves, to exactly constrain modular devices [50] and the accuracy of that alignment for injection molded parts [51]. Over- and under-constraint can introduce unpredictable dead volumes due to variability in assembly forces and feature dimensions.…”

Microfluidic Gasketless Interconnects Sealed by Superhydrophobic Surfaces

“…Passive alignment structures enable simultaneous alignment of multiple interconnects, and they can be manufactured using the established mass production techniques such as injection molding and hot embossing. Passive alignment structures also determine the gap between the two mating surfaces of two chips (or a module and a motherboard) [17,18].…”

“…The gasketless superhydrophobic fluidic interconnect (GSFI) was formed by a liquid bridge spanning the physical gap, that acts as the fluid passage. The gaps were established using passive kinematic constraints [17,18]. The failure or leakage pressure for the GSFI was calculated using the Young-Laplace equation.…”

Leakage pressures for gasketless superhydrophobic fluid interconnects for modular lab-on-a-chip systems

“…The sample chip geometry, shown schematically in Fig. 1c, consisted of three v-grooves for exact kinematic alignment, alignment standards for assessing the alignment accuracy of the assemblies 29 , elevated isolation zones to facilitate the creation of superhydrophobic surfaces around the fluid ports, and injection-molded through-holes with backside counter bores for fluidic transfer between chips. An assembly consisted of two sample chips with ball bearings seated in the v-grooves to define the gap.…”

“…Each assembly feature or interconnect removes one or more of those DOF. The use of multiple interconnects leads to either an overconstrained system, where additional force is required to assemble component chips, or an under-constrained system, when additional clearances are included around alignment features to ensure assembly 29 . In the overconstrained case, the additional assembly force is proportional to the number of interconnects and the strain it induces in the final assembly creates both indeterminate dead volumes and misalignment between the chip modules.…”