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Among various growth processes, hydrothermal synthesis has been widely employed to produce ZnO nanowires because of its simplicity and cost effectiveness. However, the successful hydrothermal synthesis of ZnO nanowires on multi-layered polymer structures has been limited due to growth inhibitors in the polymer. For example, alpha-hydroxy ketone resolved in a UV-curable polyurethane acrylate (PUA) resin forms carboxyl groups (COOH) consisting of hydroxyl groups (OH) on the -position of a carbonyl group (CO) during the UV-curing process. The carboxyl groups suppress the nucleation and growth of ZnO nanowires. In this paper, multi-layered polymer structures were fabricated by liquid transfer imprint lithography (LTIL), and the enriched carboxyl groups on the UV-cured PUA structures were pre-treated with hexamethylenetetramine (HMTA) solution to reduce the inhibitive influence of the carboxyl groups. The HMTA pre-treatment enabled ZnO nanowires to grow hydrothermally on multi-layered PUA structures despite the initial presence of carboxyl groups. Display Omitted Multi-layered polymer structures were fabricated using a polyurethane acrylate by liquid transfer imprint lithography.UV-cured PUA structures have carboxyl groups that suppress the nucleation and growth of ZnO nanowires.Carboxyl groups were pretreated in aqueous hexamethylenetetramine (HMTA) solution prior to ZnO seed layer coating.ZnO nanowires were grown on the multi-layered polymer structures by hydrothermal synthesis.

Hot embossing is one of the most popular fabrication methods to replicate polymer microdevices in the field of micro-fluidics and micro-optics. Numerical models for hot embossing were constructed to analyze the advance of flow front of the molten polymer using commercial software, DEFORM-2D. A hemisphere tipped post, used as an alignment structure in the assembly of micro devices, was modeled to demonstrate the flow behavior of the molten polymer in mold filling. Hot embossing experiments were performed to validate the feasibility of the numerical models. Most of the simulations showed agreement with experiments. The mold filling was estimated with the heights of the embossed posts in the analysis. No significant mold filling with the molten polymer was observed below the glass transition temperature of 105 °C. The mold cavity was completely filled with the polymer at the molding temperature of 137.5 °C and 150 °C while the embossing forces were 300, 600, and 900 N.

Injection molding has been widely used in the manufacturing of various polymer products, including housewares, home appliances, and automotive parts. A disposable medical device based on polymeric material at a low cost is another important area for injection molding. The numerical analysis was performed to predict the potential problem, often occurring during the manufacturing process of the medical device. Computer-aided engineering model was developed using industry-standard molding software, MOLDFLOW®. The flow pattern of the molten polymer was investigated in the replication of butterfly shaped Catheter Support for various catheterization. The flow pattern and temperature distribution of the molded part were investigated through a series of analysis. The results of analysis with original design predicted non-uniform polymer flow with a poor weld line, unbalanced cavity filling, and uneven temperature distribution of the part. An appropriate gate location to achieve uniform flow pattern for mold filling was determined on the base of the predicted results and experience, considering the performance of the product and limitation of the production.

An increasing interest in low-cost polymer micro-fabrication techniques demands an increasing necessity for characterizing such techniques. In this research, polymethylmethacrylate (PMMA) and polydimethylsiloxane (PDMS) microprisms were realized by hot embossing and replica molding processes, respectively. In both replication methods, the polymer microprisms were patterned with the same brass master mold. This mold was fabricated via high precision micro-milling, which accommodates a wide range of achievable sidewall angles and a large workable surface area relative to lithographic fabrication technologies. The pattern designed for replication contained a microprism array of 20 parallel, equal length prisms, grouped into four sets of distinct prism geometries. The four geometries include three triangular microprisms with varying interior angles and one semicircular microprism with a radius of 500 μm. The polymer microprisms replicated by PMMA hot embossing and PDMS replica molding were found to exhibit interior angle reductions relative to the brass master mold dimensions. This paper includes a description and analysis of a surface treatment process by which the RMS surface roughness of the mentioned PMMA microprisms was shown to reduce by 28 % after controlled thermal exposures just above their glass transition temperature.

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\pm 6~\mu $ m along the x -axis and from 103 ± 7 to $118\pm 11~\mu $ m along the y -axis. The vertical variation from the nominal value of $287~\mu $ m ranged from −10 ± 4 to $34\pm 7~\mu $ m. 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]

A polymer-based, multiplex single molecule detection module (SMD) was developed with a fluidic substrate and a cover plate. The fluidic substrate was fabricated using a single-step, double-sided hot embossing in poly(methyl methacrylate) (PMMA) with sampling zone microchannels on the bottom side and microlenses on the top. Shallow sampling zone microchannels (5 μm deep and 100 μm wide) were made to improve sampling efficiency and microlenses were adopted to collect the fluorescent radiation from the sampling zone microchannels. A cyclic olefin copolymer (COC) embedded waveguide in PMMA along with an integrated coupling prism was fabricated using polydimethylsiloxane (PDMS) stencils and melted COC (40% w/v in toluene) on the cover plate. The COC waveguide with a COC integrated coupling prism will be used for evanescent excitation of fluorescent samples in the sampling zone microchannels. The fluidic substrate was bonded with the cover plate using thermal fusion bonding based on a pressure-assisted boiling point control system. This approach allowed for sealing of shallow microchannels without observable sagging of the cover plate, which was confirmed by leakage testing with fluorescent dyes. The completed SMD module will be tested for characterization of the optical performances such as signal-to-noise ratio and sampling efficiency and it will provide the capability for rapid screening of stroke at low cost.Copyright © 2013 by ASME

Numerical analysis to predict the flow behavior of polymers was conducted using commercial finite element software, DEFORM-2D. An alignment structure, a hemisphere-tipped post with an annular ring, was modeled to demonstrate the flow front of the polymer during molding. The cavity filling process was evaluated by measuring the heights of the molded posts and confirmed and validated by experimental data. Estimated and measured heights showed better replication accuracy with the increase of molding temperature and embossing force. Results exposed complete cavity filling at embossing forces of 600 and 900 N at a molding temperature of 137.5°C. The FEM prediction tool can be used to select the adequate process parameters for a high fidelity replication of polymer microstructures.

The flow behavior of polymers was analyzed using a commercial finite element software, DEFORM-2D, for the replication of microstructures. An alignment structure for microassembly, a hemisphere-tipped post, was modeled to demonstrate the polymer flow in hot embossing. The mold filling with polymer was evaluated by the heights of molded posts. The results of simulation showed better replication fidelity of the post with the increase of the molding temperature and displacement of the mold insert. The complete filling of a mold cavity was achieved at the molding temperatures of 112.5, 125, 137.5, and 150°C when the displacements were 1.5, 2.0 and 2.5 mm. The model can be used to design the process parameters for the reliable replication of microstructures.

A high throughput microfluidic system including a 96 continuous flow (CF) thermal reactors and a multi-zone thermal control system was designed and fabricated. An infrared camera (IR) was used to analyze and verify the uniformity of the temperature distribution. Temperature variations from the nominal values were ±2°C in the denaturation zone and ±1°C in the renaturation and extension zones. Six different DNA fragments, with lengths ranging from 99 bp to 997 bp, were obtained from a λ-DNA template, each with a distinct renaturation temperature. As an initial demonstration of the biochemical performance of the polymerase chain reaction (PCR) reactor arrays, a column device comprised of eight 25-cycle CFPCRs was used to amplify identical PCR cocktails for each DNA fragment simultaneously at a flow velocity of 2 mm/s. All but the 997 bp were successfully amplified. Yields for the 99 bp fragment varied from 15%–36% of the amplicon on block thermal cycler. In a second experiment, a row device composed of six 25-cycle CFPCRs was used to successfully, simultaneously amplify cocktails for all six DNA fragment lengths at a flow velocity of 1 mm/s in parallel. Each device in the row had a distinct renaturation temperature to match the DNA fragment length. The parallel thermal arrays can be used in modular systems including both PCR for amplification and, for example, ligase detection reaction (LDR) for mutation detection.Copyright © 2009 by ASME

Validation of a tolerance analysis for the assembly of modular, polymer microfluidic devices was performed using simulations and experiments. A set of three v-groove and hemisphere-tipped post joints was adopted as a model assembly features. An assembly function with assembly feature dimensions and locations was modeled kinematically. Monte Carlo methods were applied to the assembly function to simulate variation of the assembly. Assembly accuracy was evaluated assuming that the variations of the assembly features were randomly distributed. The estimated mismatches were 118 ± 30 μm and 19 ± 13 μm along the X- and Y-axes, respectively. The estimated vertical gap between the modules at the alignment standards along the X- and Y-axes 312 ± 37 μm and 313 ± 37 μm, compared to the designed value of 287 μm. To validate the tolerance model, two micromilled brass mold inserts containing the assembly features and alignment standards were used to double-sided injection mold polymer parts. The accuracy of the assembly of the modular microdevices was estimated by measuring the mismatch and vertical gaps between alignment standards on each axis. The measured lateral mismatches were 103 ± 6 μm and 16 ± 4 μm along the X- and Y-axes, respectively. The vertical gaps measured for the assemblies were 316 ± 4 μm and 296 ± 9 μm at the X- and Y-axes, compared to the designed distance of 287 μm. Simulation and experimental results were in accordance with each other. The models can be used to predict the assembly tolerance of polymer microfluidic devices and have significant potential for enabling the realization of cost-effective mass production of modular instruments.Copyright © 2008 by ASME

A 96-well solid-phase reversible immobilization (SPRI) reactor plate was designed to demonstrate functional titer plate-based microfluidic platforms. Nickel, large area mold inserts were fabricated using an SU-8 based, UV-LIGA technique on 150 mm diameter silicon substrates. Prior to UV exposure, the prebaked SU-8 resist was flycut to reduce the total thickness variation to less than 5 mum. Excellent UV lithography results, with highly vertical sidewalls, were obtained in the SU-8 by using an UV filter to remove high absorbance wavelengths below 350 nm. Overplating of nickel in the SU-8 patterns produced high quality, high precision, metal mold inserts, which were used to replicate titer plate-based SPRI reactors using hot embossing of polycarbonate (PC). Optimized molding conditions yielded good feature replication fidelity and feature location integrity over the entire surface area. Thermal fusion bonding of the molded PC chips at 150 degrees C resulted in leak-free sealing, which was verified in leakage tests using a fluorescent dye. The assembled SPRI reactor was used for simple, fast purification of genomic DNA from whole cell lysates of several bacterial species, which was verified by PCR amplification of the purified genomic DNA.

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

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

A novel thermoplastic fusion bonding method using a pressure-assisted boiling point (PABP) control system was developed to apply precise temperatures and pressures during bonding. Hot embossed polymethyl methacrylate (PMMA) components containing microchannels were sealed using the PABP system. Very low aspect ratio structures (AR = 1/100, 10 μm in depth and 1000 μm in width) were successfully sealed without collapse or deformation. The integrity and strength of the bonds on the sealed PMMA devices were evaluated using leakage and rupture tests; no leaks were detected and failure during the rupture tests occurred at pressures greater than 496 kPa. The PABP system was used to seal 3D shaped flexible PMMA devices successfully.