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Microfluidic devices play an increasingly important role in healthcare-related fields, but integration of electrodes and electronic components has been restricted at the prototyping stage of product development by a limited range of fabrication methods. In this work a new fabrication methodology is presented for embedding metallic microelectrodes in thermoplastic microfluidic devices. Microelectrodes are fabricated on steel wafers by means of photolithographic patterning and electrodeposition and then transferred to a thermoplastic sheet using hot embossing, resulting in embedded metal electrodes flush with the polymer surface. The unique shape of the microelectrodes provides an anchoring mechanism that ensures structural stability and reliability of the devices. A wide variety of thermoplastics can be used in this process including polycarbonate, polymethylmethacrylate (PMMA), and cyclic olefin copolymer (COC). Devices are assembled by a solvent-assisted bonding process, after drilling the inlets and outlets. This method allows for rapid fabrication of robust embedded electrodes and wiring connections from a broad range of metals for thermoplastic microfluidic devices. Finally, embedded interdigitated microelectrodes are used to measure conductivity within a microchannel via impedance spectroscopy analysis. The use of this technology is relevant to a wide range of analytical applications. [ABSTRACT FROM AUTHOR]

Fluid dynamics and heat transfer of flow through periodic open-cellular microlattice structures are characterized for varying superficial flow orientations and flow rates to investigate heat transfer and pressure loss anisotropy. For given Reynolds number, friction factor is lowest when flow is aligned with the largest straight-through passages in the microlattice. A maximum friction factor, over twice the optimally aligned friction factor, exists for flow orientations between π/8 and π/4 rad off the optimal alignment, with little variation in friction factor for π/8 and π/4 rad. Heat transfer is maximized at π/4 rad off axis from the largest straight-through passages; however, less angular variation occurs in Nusselt number than in friction factor. Empirical correlations involving superellipses yield analytical equations describing Nusselt number dependence on flow angle and Reynolds number. This work enables selection of optimal flow orientations and optimal cellular architecture in convective heat transfer implementations of microlattice materials for lightweight and multifunctional applications. © 2012 American Institute of Chemical Engineers AIChE J, 59: 622-629, 2013 [ABSTRACT FROM AUTHOR]

The fluid dynamics of flow through microscale lattice structures is characterized for different unit cell sizes, flow angles, and flow rates. The structures consist of an octahedral-type periodic unit cell, which is formed from an interconnected pattern of self-propagating photopolymer waveguides. The periodic unit cell of each sample has a node-to-node spacing between 800 and 2400 μm and a truss member diameter between 148 and 277 μm. Water is directed through the microscale lattice structures, and the resulting pressure drop is investigated for two different flow angles and superficial flow rates between 0.5 and 4.8 L/min. Finite element analysis is used to determine pressure drop in the laminar flow regime. The results are used to develop a correlation describing friction factor as a function of flow direction, geometric characteristics, and Reynolds number. This work enables control of the fluid dynamics in microarchitected multifunctional truss materials through design and superficial flow angle. © 2010 American Institute of Chemical Engineers AIChE J, 2011 [ABSTRACT FROM AUTHOR]