Three-dimensional Microfluidic Networks Research Articles

Fabrication of Three-dimensional Paper-based Microfluidic Devices for Immunoassays

Paper wicks fluids autonomously due to capillary action. By patterning paper with hydrophobic barriers, the transport of fluids can be controlled and directed within a layer of paper. Moreover, stacking multiple layers of patterned paper creates sophisticated three-dimensional microfluidic networks that can support the development of analytical and bioanalytical assays. Paper-based microfluidic devices are inexpensive, portable, easy to use, and require no external equipment to operate. As a result, they hold great promise as a platform for point-of-care diagnostics. In order to properly evaluate the utility and analytical performance of paper-based devices, suitable methods must be developed to ensure their manufacture is reproducible and at a scale that is appropriate for laboratory settings. In this manuscript, a method to fabricate a general device architecture that can be used for paper-based immunoassays is described. We use a form of additive manufacturing (multi-layer lamination) to prepare devices that comprise multiple layers of patterned paper and patterned adhesive. In addition to demonstrating the proper use of these three-dimensional paper-based microfluidic devices with an immunoassay for human chorionic gonadotropin (hCG), errors in the manufacturing process that may result in device failures are discussed. We expect this approach to manufacturing paper-based devices will find broad utility in the development of analytical applications designed specifically for limited-resource settings.

Three-dimensional fit-to-flow microfluidic assembly

Three-dimensional microfluidics holds great promise for large-scale integration of versatile, digitalized, and multitasking fluidic manipulations for biological and clinical applications. Successful translation of microfluidic toolsets to these purposes faces persistent technical challenges, such as reliable system-level packaging, device assembly and alignment, and world-to-chip interface. In this paper, we extended our previously established fit-to-flow (F2F) world-to-chip interconnection scheme to a complete system-level assembly strategy that addresses the three-dimensional microfluidic integration on demand. The modular F2F assembly consists of an interfacial chip, pluggable alignment modules, and multiple monolithic layers of microfluidic channels, through which convoluted three-dimensional microfluidic networks can be easily assembled and readily sealed with the capability of reconfigurable fluid flow. The monolithic laser-micromachining process simplifies and standardizes the fabrication of single-layer pluggable polymeric modules, which can be mass-produced as the renowned Lego(®) building blocks. In addition, interlocking features are implemented between the plug-and-play microfluidic chips and the complementary alignment modules through the F2F assembly, resulting in facile and secure alignment with average misalignment of 45 μm. Importantly, the 3D multilayer microfluidic assembly has a comparable sealing performance as the conventional single-layer devices, providing an average leakage pressure of 38.47 kPa. The modular reconfigurability of the system-level reversible packaging concept has been demonstrated by re-routing microfluidic flows through interchangeable modular microchannel layers.

Nanofluidics in chemical analysis

Nanofluidic architectures and devices have already had a major impact on forefront problems in chemical analysis, especially those involving mass-limited samples. This critical review begins with a discussion of the fundamental flow physics that distinguishes nanoscale structures from their larger microscale analogs, especially the concentration polarization that develops at nanofluidic/microfluidic interfaces. Chemical manipulations in nanopores include nanopore-mediated separations, microsensors, especially resistive-pulse sensing of biomacromolecules, fluidic circuit analogs and single molecule measurements. Coupling nanofluidic structures to three-dimensional microfluidic networks is especially powerful and results in applications in sample preconcentration, nanofluidic injection/collection and fast diffusive mixing (160 references).

Fabrication of a poly(dimethylsiloxane) membrane with well-defined through-holes for three-dimensional microfluidic networks

We report a simple method for the fabrication of a poly(dimethylsiloxane) (PDMS) membrane with through-holes by blowing a residual prepolymer away from a photoresist (PR)-patterned Si wafer. The fabrication method for the perforated polymer membrane is crucial to achieve both complicated three-dimensional microfluidic devices and polymer sieve sheets. This method has several advantages over the previous methods in that we can repeatedly make the well-defined holes on the PDMS membranes even if the excess prepolymer remains on the PR mold after spincoating at a relatively low rpm. In addition, the desired pattern can be selectively perforated from the whole wafer even if the mold is fabricated by single-step lithography.

Monolithic fabrication of three-dimensional microfluidic networks for constructing cell culture array with an integrated combinatorial mixer

We present a novel method to monolithically fabricate three-dimensional (3-D) microfluidic networks and based on this fabrication technology, we have constructed the first cell culture device with an integrated combinatorial mixer. The device is designed for screening the combinatorial effects of multiple compound exposure on cultured cells, and a 1 cm × 1 cm proof-of-concept chip having a three-input combinatorial mixer and eight individually isolated micro culture-chambers has been fabricated. The 3-D microfluidic networks are fabricated utilizing the surface micromachining of parylene C (poly(chloro-p-xylylene)), and the monolithic method enables the device to achieve precise alignment in between microchannels and favorably obviates multilayer bonding processes. By incorporating several microfluidic “overpass” structures to allow one microfluidic channel to cross over other microfluidic channels, the combinatorial mixer is able to simultaneously generate all the combinations of the input fluidic streams for output to the microchambers. Cell culturing inside parylene C micro culture-chambers has been successfully performed, and the ability to simultaneously treat arrays of cells with different combinations of compounds has been demonstrated with experiments using three different cell stains. Our scaleable process can enable the fabrication of devices with a high-input combinatorial mixer with applications not only for high-throughput cell-based assays but also for conducting researches in combinatorial chemistry or the pharmaceutical industry. At the same time, the fabrication technique will have general applicability for building complex 3-D microfluidic devices, which can broaden the applications for current lab-on-a-chip systems.

On-chip genotoxic bioassay based on bioluminescence reporter system using three-dimensional microfluidic network

Microchip-based genotoxic bioassay using sensing Escherichia coli strains has been performed. In this method, the assay was conducted in three-dimensional microfluidic network constructed by a silicon perforated microwell array chip and two poly(dimethylsiloxane) (PDMS) multi-microchannel chips. The sensing strains having firefly luciferase reporter gene under transcriptional control of umuD as an SOS promoter were put into the channels on one of the PDMS chips and immobilized in the silicon microwells. Samples containing genotoxic substances and substrates for luciferase were into the channels on the other PDMS chip. The optimum conditions of the assay in the on-chip format have been investigated using mitomycin C (MMC) as a genotoxic substance. As a result, the dose-dependence of bioluminescence intensity was obtained at once on the chip. Additionally, the response ratios of the bioluminescence between mutagen- and non-induced strains were successfully enhanced by improving the on-chip assay methods and conditions. Several well-known genotoxic substances were subjected to the on-chip assay, and were detected with the detection limits comparable to those in the conventional method with reduced time.

Three-Dimensional Microfluidic Tissue-Engineering Scaffolds Using a Flexible Biodegradable Polymer.

Three-dimensional microfluidic networks using a flexible biodegradable polymer have been fabricated using modified microfabrication processes tailored specifically for poly(glycerol-co-sebacate). A model hepatocyte cell line (HepG2) is seeded and perfused in the microfluidic networks to demonstrate cell viability and function, which is maintained in long-term perfusion culture (see Figure; scale bar is 50 μm). The seeded, fully degradable device can potentially be integrated into a patient's existing vasculature in order to restore organ function.

Ligase Detection Reaction/Hybridization Assays Using Three-Dimensional Microfluidic Networks for the Detection of Low-Abundant DNA Point Mutations

We have fabricated a flow-through biochip assembly that consisted of two different microchips: (1) a polycarbonate (PC) chip for performing an allele-specific ligation detection reaction (LDR) and (2) a poly(methyl methacrylate) (PMMA) chip for the detection of the LDR products using an universal array platform. The operation of the device was demonstrated by detecting low-abundant DNA mutations in gene fragments (K-ras) that carry point mutations with high diagnostic value for colorectal cancers. The PC microchip was used for the LDR in a continuous-flow format, in which two primers (discriminating primer that carried the complement base to the mutation being interrogated and a common primer) that flanked the point mutation and were ligated only when the particular mutation was present in the genomic DNA. The miniaturized reactor architecture allowed enhanced reaction speed due to its high surface-to-volume ratio and efficient thermal management capabilities. A PMMA chip was employed as the microarray device, where zip code sequences (24-mers), which were complementary to sequences present on the target, were microprinted into fluidic channels embossed into the PMMA substrate. Microfluidic addressing of the array reduced the hybridization time significantly through enhanced mass transport to the surface-tethered zip code probes. The two microchips were assembled as a single integrated unit with a novel interconnect concept to produce the flow-through microfluidic biochip. A microgasket, fabricated from an elastomer poly(dimethylsiloxane) with a total volume of the interconnecting assembly of <200 nL, was used as the interconnect between the two chips to produce the three-dimensional microfluidic network. We successfully demonstrated the ability to detect one mutant DNA in 100 normal sequences with the biochip assembly. The LDR/hybridization assay using the assembly performed the entire assay at a relatively fast processing speed: 6.5 min for on-chip LDR, 10 min for washing, and 2.6 min for fluorescence scanning (total processing time 19.1 min) and could screen multiple mutations simultaneously.

Chip-Based Bioassay Using Bacterial Sensor Strains Immobilized in Three-Dimensional Microfluidic Network

A whole-cell bioassay has been performed using Escherichia coli sensor strains immobilized in a chip assembly, in which a silicon substrate is placed between two poly(dimethylsiloxane) (PDMS) substrates. Microchannels fabricated on the two separate PDMS layers are connected via perforated microwells on the silicon chip, and thus, a three-dimensional microfluidic network is constructed in the assembly. Bioluminescent sensor strains mixed with agarose are injected into the channels on one of the two PDMS layers and are immobilized in the microwells by gelation. Induction of the firefly luciferase gene expression in the sensor strains can be easily carried out by filling the channels on the other layer with sample solutions containing mutagen. Bioluminescence emissions from each well are detected after injection of luciferin/ATP mixtures into the channels. In this assay format using two multichannel layers and one microwell array chip, the interactions between various types of samples and strains can be monitored at each well on one assembly in a combinatorial fashion. Using several genotypes of the sensor strains or concentrations of mitomycin C in this format, the dependence of bioluminescence on these factors was obtained simultaneously in the single screening procedure. The present method could be a promising on-chip format for high-throughput whole-cell bioassays.

Using three-dimensional microfluidic networks for solving computationally hard problems

This paper describes the design of a parallel algorithm that uses moving fluids in a three-dimensional microfluidic system to solve a nondeterministically polynomial complete problem (the maximal clique problem) in polynomial time. This algorithm relies on (i) parallel fabrication of the microfluidic system, (ii) parallel searching of all potential solutions by using fluid flow, and (iii) parallel optical readout of all solutions. This algorithm was implemented to solve the maximal clique problem for a simple graph with six vertices. The successful implementation of this algorithm to compute solutions for small-size graphs with fluids in microchannels is not useful, per se, but does suggest broader application for microfluidics in computation and control.