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Peer-reviewed articles


Ramaswamy,M., Ho,B., Phan,C. M., Qin,N., Ren,C. L., Jones,L. Inexpensive and rapid fabrication of PDMS microfluidic devices for biological testing applications using low cost commercially available 3D printers Journal of Micromechanics and Microengineering 2023;Online ahead of print [ Show Abstract ]

Polydimethylsiloxane (PDMS) elastomers have been extensively used in the development of microfluidic devices, capable of miniaturizing biomolecular and cellular assays to the microliter and nanoliter range, thereby increasing the throughput of experimentation. PDMS has been widely used due to its optical clarity and biocompatibility, among other desirable physical and chemical properties. Despite the widespread use of PDMS in microfluidic devices, the fabrication process typically requires specialized facilities, instruments, and materials only available in a limited number of laboratories. To expand microfluidic research capabilities to a greater scientific population, we developed and characterized a simple and robust method of fabricating relatively inexpensive PDMS microfluidic devices using readily available reagents and commercially available 3D printers. The moulds produced from the 3D printers resolve designed microfluidic channel features accurately with high resolution ( >100 µm). The critical physical and chemical post-processing modifications we outline here are required to generate functional and optically clear microfluidic devices.

Scientific Presentations


Ho B, Phan CM, Ramasamy M, Hui A, Jones L. PDMS microfluidic devices fabricated from commercial 3D printers support growth of viable HCECs and enable cell biological assays for low-cost high-throughput screening The Association for Research in Vision and Ophthalmology, New Orleans, LA, USA, April, 2023 [ Show Abstract ]

Purpose: To integrate human corneal epithelial cells (HCECs) into a PDMS microfluidic chip fabricated from a novel 3D printing method to perform cell biological assays.
Introduction: The advent of microfluidic devices has enabled tight control over the physical and chemical cellular environment in vitro, while allowing for large-scale imaging and biochemical reactions at single-cell resolution. These devices are capable of miniaturizing assays to the microliter and nanoliter range, thereby increasing assay throughput with high sensitivity, a feature that is highly advantageous in high-throughput cell-based screens. Polydimethylsiloxane (PDMS) has been widely used in microfluidics devices due to its optical clarity and non-toxicity to cells, among other desirable features. However, the fabrication of PDMS devices traditionally requires specialized facilities and instruments. Additionally, PDMS itself is highly hydrophobic and does not support mammalian cellular viability and growth.

Methods: PDMS devices were cured in 3D-printed moulds generated using the FormLabs stereolithography (SLA) printer (FormLabs 3B+, FormLabs, Somerville, MA). These devices were sterilized by autoclaving, and coated with 0.01% polydopamine (PDA) and 20μg/mL collagen. HCECs were seeded onto the device, and allowed to grow for 18-36 hours in DMEM/F12 media at 37oC. HCECs were imaged by light microscopy, and viability was assessed by alamarBlue assays.

Results: Here, we present a novel and simple method of generating PDMS microfluidic devices suitable for mammalian cell biology assays using commercial 3D printing. We show that PDMS devices coated with polydopamine (PDA) support the growth of human corneal epithelial cells (HCECs) that are metabolically active (~60-90% viability) and are comparable to HCECs cultured in standard tissue culture plastic consumables. Finally, HCECs cultured in our devices are capable of growth with fluid flow rates of up to 1mm/s.

Conclusion: Our study shows that PDMS devices manufactured through the aid of a novel 3D printing pipeline support the growth of HCECs. We aim to utilize these microfluidic devices as a tool to screen different compounds and formulations while assessing cellular viability and acquiring high resolution microscopic and fluorescence images of HCECs.

Phan CM, Ramasamy M, Ho B, Hui A, Jones L. Fabrication of a microfluidic chip using 3D printing for evaluating ocular cytotoxicity The Association for Research in Vision and Ophthalmology, New Orleans, LA, USA, April, 2023 [ Show Abstract ][ PDF ]

Purpose: To develop a PDMS (polydimethyl siloxane) microfluidic chip to evaluate ocular cytotoxicity with ophthalmic formulations and materials.

Methods: The microfluidic chip was designed using CAD software (FreeCAD), and the moulds of the chips were printed using (1) a stereolithography (SLA) and (2) digital light processing (DLP) 3D printer. The printed moulds were washed with isopropyl alcohol (IPA), UV-cured for 1-hour at 60oC, followed by heating in an oven at 120oC for 2 hours to remove any unreacted polymers. The surface of the chips was smoothed with sandpaper with increasing grit, followed by an application of nail polish. The moulds were then cast with PDMS, a gas-permeable and clear polymer commonly used for the fabrication of microfluidic chips. The moulds and chips were imaged using SEM (scanning electron microscopy). The light transmittance of the chips was also measured. The PDMS top half of the chip was adhered to a microscope slide using medical-grade double-sided tape. For a pilot study, the PDMS chips were sterilized via autoclaving, coated with 0.1% polydopamine to improve their surface wettability, and then seeded with immortalized human corneal epithelial cells (HCEC). After 2 days of incubation in a nutrient media broth (no flow), cell adhesion and growth were evaluated using light microscopy.

Results: Both 3D printers were able to print moulds with high resolution, with channel dimensions as low as 50 µm, and with faster print times for the DLP printer. SEM images revealed that moulds that were both sanded and had a nail coating were significantly smoother than the original 3D-printed moulds. The chips cast from the polished moulds were transparent, with >85% transmittance from 450-700 nm, and could be used to image cells through a microscope. The microfluidic chips were able to handle flow rates up to 1 mL/min for 24 hours without any signs of leakage. HCEC cells were able to adhere and grow on the coated PDMS microfluidic chip after 2 days.

Conclusion: This study showed that SLA and DLP printers could be used to fabricate PDMS microfluidic chips as a low-cost rapid prototyping approach. The fabricated chips were clear and could be used to incorporate HCEC cells. Future work will examine the viability of cells under different flow rates and shear stress conditions on these chips.

Ramasamy M, Ho B, Phan CM, Jones L. Fabrication of a microfluidic chip for ophthalmic drug delivery studies using 3D printing The Association for Research in Vision and Ophthalmology, New Orleans, LA, USA, April, 2023 [ Show Abstract ]

Purpose: To develop a microfluidic chip for testing the release of ocular drugs from soft contact lenses using 3D printing.

Methods: The microfluidic chips were designed using CAD (computer-aided design) software consisting of a top and bottom portion. The top portion comprised of inlet, outlet, and channels for fluid flow. The lower portion contained a dome-shaped mount to mount a contact lens. The chips were printed using clear resin on a commercial stereolithography (SLA) 3D-printer. The printed chips were washed in isopropyl alcohol (IPA) for 30 minutes, air dried and UV cured for 30 minutes. The top and bottom portions of the chip were fused by applying a thin layer of resin, followed by UV-curing for 10 minutes. In another design iteration, moulds for the chips were 3D printed and casted with polydimethylsiloxane (PDMS). The two halves of the PDMS chips were fused using double-sided adhesive tape. In a preliminary study, two commercial contact lenses, etafilcon A and senofilcon A, were soaked in 2 ml of red food dye for 2 hours. The release of the dye was measured using the PDMS chip with phosphate-buffered saline at a flow rate of 1.5 L/min over 24 hours via absorbance at 520 nm. The dye extraction from both lenses was
performed by incubating the dye-soaked lenses in 1:1 acetonitrile/water solution for 24 hours with gentle shaking.

Results: Both the chip and moulds were printed in less than 5 hours, with a minimum resolution of 50 μm. The resulting resin and PDMS chips can also be sterilized by autoclaving. The top and bottom parts of the chips were completely sealed such that no leakage was detected at a flow rate of up to 100 μL/min for 24 hours. The release kinetics of the dye was linear throughout the 24 h period for both lens types under the current parameters. The total amount of dye released after 24 h was higher for etafilcon A (26.26 mg/lens) than senofilcon A (18.41 mg/lens), which corresponded to approximately 83.1% and 40.01% release, respectively. Both the lens types were still visibly red after 24 hours. The output of the microfluidic chip could be used as an input for subsequent analyses.

Conclusions: This study showed a cost- and time-efficient approach to fabricate a microfluidic chip for evaluating drug release from contact lenses. Future work will examine the release profile of various ocular drugs from contact lenses using different flow conditions.