Transparent Microfluidic 3D Printing - Jianlin Zhou

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CHEM-ENG 535: Microfluidics and Microscale Analysis in Materials and Biology

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3D Printing in Microfluidic Device

Figure 1: Microscopic view of the cross-section part printed via FDM[1]

3D printing is being used widely under commercial and laboratory setting. Commonly, microfluidic channels were produced using a mold that transfer the channel patterns into the substrate. The mold can be made under lithography and 3D printing, etc. Since the 3D printing have a great range of resolution, lithography is preferred under many laboratories setting[2]. However, the process complexity and low production rate are the main drawbacks. The automation of printing integrated microfluid devices, which eliminates the hands-on processing, might be the future of microfluid devices.

The most commercially available type of printing style is Fused Deposition Modeling (FDM), which uses opaque filament and it generally have poor printing resolution. In addition, the FDM printed parts have large void space and adhesion quality irregularity. Transparency and high resolution are fundamental for microfluidic applications. In some cases, certain rigidity is critical as well. Under such restrictions, the Stereolithography (SLA) suits the best, by using the commercially available clear resin from FormLabs. Its current SLA 3D printer have the xy-axis resolution of 25 μm[3]. Compared to the limitation of printing PDMS, the use of clear resin and Formlab SLA printer is highly competitive[4] [5].

Materials

In general, the photopolymer solution contains monomer, oligomer, and photo-initiator [2] [6].Based on the clear resin printing technology, the raw materials of the solution are Urethane dimethacrylate (UDMA), Methacrylate Monomer(s) and Diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide[7].

Stereolithography Process

Upon printing, a thin layer of photopolymer solution is targeted by the light sources which can be a scanning laser or a digital light projector (DLP)[2]. Based on the printing part, the light source would trace the desired 2D cross section pattern. The photo-initiator would respond and initiate the polymerization reaction locally. After the entire 2D pattern were traced, the platform will be raised or lowered, depending on the printing style, allowing new layer to be printed. Then, the printing cycle continues until completion[8] [5].

Polymerization

Figure 2: Polymerization steps of PEGDA initiated by Diphenyl(2,4,6- trimethylbenzoyl)phosphine oxide[6] [7]

There are three steps of polymerization:

  1. Initiation
  2. Propagation
  3. Termination

The UV induced initiation step is depicted in figure 2. The initiator molecules form free radicals that combine with the monomers and oligomers under the UV light. The radicalized monomers and oligomers then react and bond with each other[5].

Post Processing

Figure 3: 3D printed microfluidic chip using clear resin by Formlabs[9]

References

  1. ↑ Guide to Stereolithography (SLA) 3D Printing, https://formlabs.com/blog/ultimate-guide-to-stereolithography-sla-3d-printing/(accessed 3/27/2022)
  2. ↑ 2.0 2.1 2.2 Waheed, S., Cabot, J. M., Macdonald, N. P., Lewis, T., Guijt, R. M., Paull, B., & Breadmore, M. C. (2016). 3D printed microfluidic devices: enablers and barriers. Lab on a Chip, 16(11), 1993-2013. https://doi.org/10.1039/C6LC00284F
  3. ↑ Materials Library. https://formlabs-media.formlabs.com/filer_public/ac/89/ac8963db-f54a-4cac-8fe9-fb740a7b06f1/formlabs-materials-library.pdf (accessed 3/27/2022)
  4. ↑ Comina, G., Suska, A., & Filippini, D. (2014). PDMS lab-on-a-chip fabrication using 3D printed templates. Lab on a Chip, 14(2), 424-430. https://doi.org/10.1039/c3lc50956g
  5. ↑ 5.0 5.1 5.2 Mendes‐Felipe, C., Oliveira, J., Etxebarria, I., Vilas‐Vilela, J. L., & Lanceros‐Mendez, S. (2019). State‐of‐the‐art and future challenges of UV curable polymer‐based smart materials for printing technologies. Advanced Materials Technologies, 4(3). https://doi.org/10.1002/admt.201800618
  6. ↑ 6.0 6.1 Yang, W., Yu, H., Liang, W., Wang, Y., & Liu, L. (2015). Rapid fabrication of hydrogel microstructures using UV-induced projection printing. Micromachines, 6(12), 1903-1913. https://doi.org/10.3390/mi6121464
  7. ↑ 7.0 7.1 Clear Resin; MSDS No. FLGPCL04[Online]; Formlabs, Inc: Somerville, MA, February 25, 2020. https://formlabs-media.formlabs.com/datasheets/1801037-SDS-ENEU-0.pdf(accessed 3/27/2022)
  8. ↑ Nielsen, Anna V., et al. "3D printed microfluidics." Annual Review of Analytical Chemistry 13 (2020): 45-65.https://doi.org/10.1146/annurev-anchem-091619-102649
  9. ↑ Guide to Clear 3D Printing, https://formlabs.com/blog/3d-printing-transparent-parts-techniques-for-finishing-clear-resin/(accessed 3/27/2022)
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