title: 3D printed miniaturised analytical devices (3D MADe)
Creators: name: Gupta, V
Publisher: name: University of Tasmania
Year: 2018

description: 3D printing has gained popularity in almost every field of research, development, and manufacturing due to its ability to fabricate complex three-dimensional prototypes and functional devices with relative ease, which was unimaginable in the past. Herein, different 3D printing techniques have been studied to understand their capabilities and potential to miniaturise and increase the performance of analytical devices. In particular, selective laser melting and PolyJet 3D printing techniques have been used to develop new functional 3D printed miniaturised analytical devices with three-dimensional micro- and milli-fluidic channels.
An initial study was undertaken to assess the ability of selective laser melting technique to fabricate 600 mm long, 0.9 mm I.D. stainless steel (316L) and titanium alloy (Ti-6Al-4V) columns within a footprint of 5 × 30 × 30 mm. The 3D printed stainless steel column was slurry packed with octadecyl silica particles, and it was used for liquid chromatographic separations of small molecules. This study provided a proof of concept for the use of selective laser melting technique to fabricate miniaturised metallic capillary liquid chromatographic columns. However, these 3D printed columns resulted in a channel wall roughness of 20 μm, which limited the chromatographic performance of the slurry packed liquid chromatographic columns. Accordingly, the 3D printed titanium column was functionalised with in-column thermally polymerised poly(butyl methacrylate-\(co\)-ethylene glycol dimethacrylate) (BuMA-\(co\)-EDMA) monolith to circumvent the limitation of channel wall roughness. Silanisation of thermally oxidised titanium channel walls allowed a successful covalent wall bonding between the titanium column and the acrylate monolith. The prepared monolithic column was successfully used for reversed-phase liquid chromatographic (RPLC) separations of intact proteins and peptides. The use of a Peltier thermoelectric module based heating/cooling system allowed the generation of rapid temperature gradients to further improve the RPLC separations of the intact proteins.
The initial study was then extended to explore the ability of 3D printing techniques to design and fabricate geometrically complex 3D column geometries. Three different column geometries were designed and 3D printed in titanium, namely 2D serpentine, 3D spiral, and 3D serpentine. These columns were used to perform an investigation into the effect of 3D column geometry on the liquid chromatographic efficiencies of monolithic columns. All three columns allowed successful in-column thermal polymerisation of mechanically stable and uniform poly(BuMA-\(co\)-EDMA) monoliths. Van Deemter plots indicated higher liquid chromatographic efficiencies of the chromatographic columns with higher aspect ratio turns at higher linear velocities and smaller analysis time as compared to their counterpart columns with lower aspect ratio turns. Computational fluid dynamic (CFD) simulations of a basic monolithic structure indicated 44%, 90%, 100%, and 118% higher flow through narrow channels in the curved monolithic configuration as compared to the straight monolithic configuration at linear velocities of 1 mms\(^{-1}\), 2.5 mms\(^{-1}\), 5 mms\(^{-1}\), and 10 mms\(^{-1}\), respectively. An improvement in the interaction between wide and narrow channels in high aspect ratio coiled columns offers a possible explanation behind the above-mentioned trends in the Van Deemter plots. Use of the highly convoluted 3D serpentine column at higher flow rates as compared to the less convoluted 3D spiral column allowed 58% reduction in the analysis time and 74% increase in the peak capacity for the isocratic separations of the small molecules and the gradient separations of the proteins, respectively.
In addition to the use of the selective laser melting 3D printing technique to fabricate metallic miniaturised analytical devices, the use of the PolyJet 3D printing technique was also explored to fabricate polymeric miniaturised analytical devices. The PolyJet 3D printing technique was successfully used to fabricate a new transparent polymer radial flow-cell for chemiluminescence detection (CLD). The PolyJet 3D printed radial flow-cell resulted in an increase in both the signal magnitude and duration for CLD of H\(_2\)O\(_2\). The new flow-cell design provided an average increase in the peak height of 63% and 58%, in peak area of 89% and 90%, and in peak base width of 41% and 42%, as compared to its coiled-tubing spiral flow-cell and PolyJet 3D printed spiral flow-cell, respectively. CFD simulations indicated that the higher spatial coverage near the inlet and the lower linear velocities in the radial flow-cell could be contributing towards its higher signal magnitude and higher signal duration, respectively. The PolyJet 3D printed radial flow-cell was applied within a developed selective, sensitive, and reproducible ion chromatography coupled chemiluminescence detection (IC-CLD) assay for the determination of H\(_2\)O\(_2\) (a biomarker) in urine and coffee extract samples.