Article pubs.acs.org/ac
Cost-Effective Three-Dimensional Printing of Visibly Transparent Microchips within Minutes Aliaa I. Shallan,†,‡ Petr Smejkal,† Monika Corban,‡ Rosanne M. Guijt,‡ and Michael C. Breadmore*,† †
Australian Centre for Research on Separation Science (ACROSS), School of Physical Sciences Chemistry, University of Tasmania, Dobson Road (off Churchill Avenue), Sandy Bay, Tasmania 7005, Australia ‡ Australian Centre for Research on Separation Science (ACROSS), Pharmacy School of Medicine, University of Tasmania, Dobson Road (off Churchill Avenue), Sandy Bay, Tasmania 7005, Australia ABSTRACT: One-step fabrication of transparent threedimensional (3D) microfluidic to millifluidic devices was demonstrated using a commercial 3D printer costing $2300 with 500 mL of clear resin for $138. It employs dynamic mask projection stereolithography, allowing fast concept-to-chip time. The fully automated system allows fabrication of models of up to 43 mm × 27 mm × 180 mm (x × y × z) at printing speeds of 20 mm/h in height regardless of the design complexity. The minimal cross sectional area of 250 μm was achieved for monolithic microchannels and 200 μm for positive structures (templates for soft lithography). The colorless resin’s good light transmittance (>60% transmission at wavelengths of >430 nm) allows for on-chip optical detection, while the electrically insulating material allows electrophoretic separations. To demonstrate its applicability in microfluidics, the printer was used for the fabrication of a micromixer, a gradient generator, a droplet extractor, and a device for isotachophoresis. The mixing and gradient formation units were incorporated into a device for analysis of nitrate in tap water with standard addition as a single run and multiple depth detection cells to provide an extended linear range.
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microfluidic devices. A hybrid printer, Objet’s Eden 250, combines jetting of photocurable resin with photopolymerization and was reported by Bonyár to make soft lithography templates (width, 4 mm; height, 300 μm) and microfluidic devices containing a mixer and homogenizer for gynecological cervical sample preparation (channel height, 1 mm; width, 2 mm).9 A similar printer, Objet Connex 350, was used to fabricate fluidic devices (3 mm wide and 1.5 mm deep channels) for drug transport studies.10 These studies show limited resolution of FDM printers when they are printing closed channels. Dimensions were in the millimeter range as flushing the support material is more difficult in narrower channels. Printing without the supporting material is limited to designs devoid of large enclosed structures like circular channels (800 μm diameter). Photofabrication or “stereolithography” (SL) is perhaps the oldest and most well-known additive fabrication method. The first SL system used a computer-controlled focused laser beam to polymerize resin using the vector approach (point-to-point line drawn in three dimensions). This was first presented in 1986 and commercialized in 1988,6 and at present, structures can be realized within a few hours.11 Printers employing
hen fast concept-to-chip time is a priority, one-step manufacturing techniques are favored over conventional methods.1 Conventional photolithographic methods struggle with three-dimensional (3D) designs as accurate alignment and bonding of several layers are crucial to realize the 3D structure. The ability to transform digital designs directly into physical models, without the need for masks, will not only accelerate the fabrication process but also make practical evaluation of different designs faster and easier. 3D manufacturing techniques can be subtractive through removal of material with techniques such as femtosecond laser direct writing2 or additive through fused deposition modeling (FDM)3−5 or photofabrication.6,7 Additive methods in particular have rapidly improved over the past decade, and there are now a number of different approaches and materials that can be used.8 FDM employs a heated nozzle to extrude a thermoplastic polymer that solidifies forming structures. McDonald et al. were the first to print templates for casting polydimethylsiloxane (PDMS) and microchip interfaces using the FDM-based Thermojet printer.3 Also FDM-based, Dimension SST 768 and 3DTouch were reported for printing centrifugal devices with 254 μm × 254 μm capillary valves4 and reaction ware with 800 μm diameter channels,5 respectively. FDM resolution is limited by nozzle size, resulting in a minimal feature size of 250 μm and a surface roughness of ≈8 μm. The opaque polymer used to fabricate these devices is not compatible with the use of organic solvents, limiting the scope for directly printed © 2014 American Chemical Society
Received: December 23, 2013 Accepted: February 10, 2014 Published: February 10, 2014 3124
dx.doi.org/10.1021/ac4041857 | Anal. Chem. 2014, 86, 3124−3130
Analytical Chemistry
Article
Figure 1. Miicraft 3D printer. (a) Printing process in progress. A pico-projector below the resin vat (not shown here) projects spatially resolved patterns from the bottom up on the resin through a clear window. First, the stage and pick move down, leaving a 50 μm gap between the pick and the bottom of the resin vat. After each exposure and waiting time, the stage moves up and then down, leaving a 50 μm gap. The process is repeated until the model is created upside down. The model is then rinsed with isopropyl alcohol, air-dried, and postcured for 10 min in the postcure chamber. (b) Printer with the front doors open showing the printing unit on the left and the postcuring unit on the right. The dashed line shows the position of the resin vat in panel a but with the stage at the top in preparation for printing the next object. The printer size is 20.5 cm × 20.8 cm × 33.5 cm (width × depth × height) and weighs 6.5 kg.
3D printers and has an x−y pixel size of 56 μm × 56 μm and a preset Z resolution of 50 or 100 μm. The presented characterization data and the variety of microfluidic applications demonstrate the potential of this printer for fast concept-tochip fabrication of lab-on-a-chip devices. The low cost of the printer makes microfluidic fabrication more readily available to a wider range of researchers, especially those who do not have access to substantial funding.
dynamic digital masks for layer-by-layer projection are faster, cheaper, and more robust than vector-operated printers, as only one translational stage (the Z axis) is required. Also, lasers can be substituted with less expensive components. Digital masks are currently generated using a liquid crystal display (LCD),12 a digital micromirror device (DMD),13,14 or a liquid crystal on silicon (LCoS).15 Although commercial 3D printers have been available since 1988, three limitations currently restrict their widespread uptake in microfluidics. First, except for few examples, the resolution is often incapable of producing a usable microchip because the print process is always a compromise among resolution, processing time, and final print size. Very highresolution systems are capable of printing only objects that are a few millimeters in dimension and therefore too small to be used as a microfluidic device. The second is the use of an appropriate resin that is cheap to use and has suitable mechanical, optical, electrical, and chemical properties. Most printers use opaque materials, which are not suitable when imaging of the process is required, for example, for studying fluid dynamics. The third is the price of the printer. Most of the printers that meet the requirement of a print resolution of
