Niall P. Macdonald

Comparing Microfluidic Performance of Three-Dimensional (3D) Printing Platforms

Three-dimensional (3D) printing has emerged as a potential revolutionary technology for the fabrication of microfluidic devices. A direct experimental comparison of the three 3D printing technologies dominating microfluidics was conducted using a Y-junction microfluidic device, the design of which was optimized for each printer: fused deposition molding (FDM), Polyjet, and digital light processing stereolithography (DLP-SLA). Printer performance was evaluated in terms of feature size, accuracy, and suitability for mass manufacturing; laminar flow was studied to assess their suitability for microfluidics. FDM was suitable for microfabrication with minimum features of 321 ± 5 μm, and rough surfaces of 10.97 μm. Microfluidic devices >500 μm, rapid mixing (71% ± 12% after 5 mm, 100 μL/min) was observed, indicating a strength in fabricating micromixers. Polyjet fabricated channels with a minimum size of 205 ± 13 μm, and a surface roughness of 0.99 μm. Compared with FDM, mixing decreased (27% ± 10%), but Polyjet printing is more suited for microfluidic applications where flow splitting is not required, such as cell culture or droplet generators. DLP-SLA fabricated a minimum channel size of 154 ± 10 μm, and 94 ± 7 μm for positive structures such as soft lithography templates, with a roughness of 0.35 μm. These results, in addition to low mixing (8% ± 1%), showed suitability for microfabrication, and microfluidic applications requiring precise control of flow. Through further discussion of the capabilities (and limitations) of these printers, we intend to provide guidance toward the selection of the 3D printing technology most suitable for specific microfluidic applications.

One-Step Fabrication of a Microfluidic Device with an Integrated Membrane and Embedded Reagents by Multimaterial 3D Printing.

One of the largest impediments in the development of microfluidic-based smart sensing systems is the manufacturability of integrated, complex devices. Here we propose multimaterial 3D printing for the fabrication of such devices in a single step. A microfluidic device containing an integrated porous membrane and embedded liquid reagents was made by 3D printing and applied for the analysis of nitrate in soil. The manufacture of the integrated, sealed device was realized as a single print within 30 min. The body of the device was printed in transparent acrylonitrile butadiene styrene (ABS) and contained a 400 μm wide structure printed from a commercially available composite filament. The composite filament can be turned into a porous material through dissolution of a water-soluble material. Liquid reagents were integrated by briefly pausing the printing before resuming for sealing the device. The devices were evaluated by the determination of nitrate in a soil slurry containing zinc particles for the reduction of nitrate to nitrite using the Griess reagent. Using a consumer digital camera, the linear range of the detector response ranged from 0 to 60 ppm, covering the normal range of nitrate in soil. To ensure that the sealing of the reagent chamber is maintained, aqueous reagents should be avoided. When using the nonaqueous reagent, the multimaterial device containing the Griess reagent could be stored for over 4 days but increased the detection range to 100-500 ppm. Multimaterial 3D printing is a potentially new approach for the manufacture of microfluidic devices with multiple integrated functional components.

Direct production of microstructured surfaces for planar chromatography using 3D printing

Through optimization of the printing process and orientation, a suitably developed surface area has been realized upon a 3D printed polymer substrate to facilitate chromatographic separations in a planar configuration. Using an Objet Eden 260VS 3D printer, polymer thin layer chromatography platforms were directly fabricated without any additional surface functionalization and successfully applied to the separation of various dye and protein mixtures. The print material was characterized using gas chromatography coupled to mass spectrometry and spectroscopic techniques such as infrared and Raman. Preliminary studies included the separation of colored dyes, whereby the separation performance could be visualized optically. Subsequent separations were achieved using fluorescent dyes and fluorescently tagged proteins. The separation of proteins was affected by differences in the isoelectric point (pI) and the ion exchange properties of the printed substrate. The simple chromatographic separations are the first achieved using an unmodified 3D printed stationary phase.

Using Printing Orientation for Tuning Fluidic Behavior in Microfluidic Chips Made by Fused Deposition Modeling 3D Printing

Fluidic behavior in microfluidic devices is dictated by low Reynolds numbers, complicating mixing. Here, the effect of the orientation of the extruded filament on the fluidic behavior is investigated in fused deposition modeling (FDM) printed fluidic devices. Devices were printed with filament orientations at 0°, 30°, 60°, and 90° to the direction of the flow. The extent of mixing was observed when pumping yellow and blue solutions into the inlets of a Y-shaped device, and measuring the extent of mixing of two colored solutions under different angles and at flow rates of 25, 50, and 100 μL/min. Fluidic devices printed with filament extruded at 60° to the flow showed the highest mixing efficiency, but results obtained at 30° suggested more complex fluid movement, as the measured degree of mixing decreased along the fluidic channel at higher flow rates. To explore this, a device with -37° filament orientation on the top surface was designed to align with the direction of the first fluid input channel and +37° on the bottom surface of the channel to align with the direction of the second fluidic input. Results indicated a rotational movement of the fluids down the microchannel, which were confirmed by computational fluid dynamics. These results demonstrate the impact of the filament extrusion direction on fluidic behavior in microfluidic devices made by FDM printing. Two chips with laminar flow (0° filament direction) or mixing flow (+37/-37° filament direction) were used to perform isotachophoresis and colorimetric detection of iron in river water, respectively, demonstrating the simplicity with which the same device can be tuned for different applications simply by controlling the way the device is printed.

Fibre-based electrofluidics on low cost versatile 3D printed platforms for solute delivery, separations and diagnostics; from small molecules to intact cells

A novel and effective fibre-based microfluidic methodology was developed to move and isolate charged solutes, biomolecules, and intact bacterial cells, based upon a novel multi-functional 3D printed supporting platform, with potential applications in the fields of microfluidics and biodiagnostics. Various on-fibre electrophoretic techniques are demonstrated to separate, pre-concentrate, move, split, or cut and collect the isolated zones of target solutes, including proteins and live bacterial cells. The use of knotting to link different fibre materials, and the unique ability of this approach to physically concentrate solutes in different locations are shown such that the concentrated solutes can be physically isolated and easily transferred to other fibres. Application of this novel fibre-based technique within a potential diagnostic platform for urinary tract infection is shown, together with the post-electrophoretic incubation of live bacterial cells, demonstrating the cell survival following on-fibre electrophoretic concentration.

3D Printed Micrometer-Scale Polymer Mounts for Single Crystal Analysis

3D printed micrometer-scale polymer mounts for single crystal analysis have been prepared by photopolymerization using digital light projection stereolithography (DLP-SLA), with a commercially available digital light projection stereolithography printer (US

Enhanced physicochemical properties of polydimethylsiloxane based microfluidic devices and thin films by incorporating synthetic micro-diamond

4000) and 3DM-ABS resin (US

3D printed microfluidic devices: enablers and barriers

150 per liter). The polymer mounts were prepared in batches of 49 in 1 h 15 min, which allowed for rapid prototyping and testing of new crystal mounting designs, with a resin cost of 0.2¢ US per mount. The suitability of the 3D printed mounts for single crystal crystallography has been demonstrated through their use in Cu Kα X-ray diffraction experiments of Rochelle salt (sodium potassium tartrate), the protein lysozyme, and has been employed for routine crystallographic analysis of organic and inorganic materials.

Fibre-based platforms for microfluidics, sensing and diagnostic applications

Synthetic micro-diamond-polydimethylsiloxane (PDMS) composite microfluidic chips and thin films were produced using indirect 3D printing and spin coating fabrication techniques. Microfluidic chips containing up to 60 wt% micro-diamond were successfully cast and bonded. Physicochemical properties, including the dispersion pattern, hydrophobicity, chemical structure, elasticity and thermal characteristics of both chip and films were investigated. Scanning electron microscopy indicated that the micro-diamond particles were embedded and interconnected within the bulk material of the cast microfluidic chip, whereas in the case of thin films their increased presence at the polymer surface resulted in a reduced hydrophobicity of the composite. The elastic modulus increased from 1.28 for a PDMS control, to 4.42 MPa for the 60 wt% composite, along with a three-fold increase in thermal conductivity, from 0.15 to 0.45 W m−1 K−1. Within the fluidic chips, micro-diamond incorporation enhanced heat dissipation by efficient transfer of heat from within the channels to the surrounding substrate. At a flow rate of 1000 μL/min, the gradient achieved for the 60 wt% composite chip equalled a 9.8 °C drop across a 3 cm long channel, more than twice that observed with the PDMS control chip.