Understanding the multiphase process in Laser-Induced-Forward-Transfer (LIFT) bioprinting from thermofluids perspective

Ben Xu

Presidential Frontier Faculty
Department of Mechanical Engineering, University of Houston


Three-dimensional (3D) bioprinting is an emerging technology that covers the knowledge of biology, materials science, and engineering. It has been widely adopted in the field including bio-scaffold fabrication and artificial organ generation (Ozbolat, 2015; Murphy and Atala, 2014). Laser-Induced-Forward-Transfer (LIFT) bioprinting is one of the laser-assisted bioprinting technologies, due to its great advantages in high printing resolution and cell viability, LIFT bioprinting has drawn increasing attention in the field of regenerative medicine (Koch et al., 2010; Morales et al., 2017). In the LIFT bioprinting process, a laser beam passes through a focusing lens, then focuses on the bottom side of a transparent quartz (donor slide). The donor slide is coated with bioink, which is a mixture of live cells and any natural or synthetic polymers (such as hydrogels and matrigels) (Antoshin et al., 2019; Pirlo et al., 2012). Those polymers with biocompatible components and favorable properties can be used as the cell-laden media. With the deepening of LIFT bioprinting technology in recent years, an energy absorbing layer (EAL) is coated between the donor slide and the bioink or printing materials (Riester et al., 2016; Smausz et al., 2006), it can be used to avoid the direct contact of pulse laser and enhance the energy absorbing rate (Sorkio et al., 2018; Gruene et al., 2011; Dias et al., 2014). Once the printing process starts, the laser will irradiate on the donor slide glass, then focus on the interface between the donor slide glass and the EAL. After the bioink absorbs enough energy from the laser, a bubble will be generated inside the bioink layer. The laser-induced bubble will then expand and collapse to form a jet flow in a very short time (less than 10 μs) (Xiong et al., 2017). When the jet reaches the bottom receptive slide, the material transfer process is completed (Qu et al., 2021; Dou et al., 2021). Figure 1 shows the schematic for the jet generation process during the LIFT process and some possible printed patterns in different jet regimes. Apparently, the stable jet is preferred for an organized printing pattern on the receptive slide, since this will lead to a good printing quality.

The schematic for the jet generation process during LIFT and different printed patterns and jet regimes due to various operating parameters (Qu et al., 2021; Dou et al., 2021).

Figure 1. The schematic for the jet generation process during LIFT and different printed patterns and jet regimes due to various operating parameters (Qu et al., 2021; Dou et al., 2021).

The formation of jet during the LIFT printing process is complex, many operating parameters, including input laser energy, bioink layer thickness, and the rheology of the bioink will influence the jet regime and the associated printing patterns. During the LIFT printing, as shown in Fig. 1, when the generated jet does not have enough momentum, the jet is not fully developed and cannot reach the bottom receptive slide to complete the transfer. In some cases, the jet may splash or create a plume of drops, and it eventually leads to an unorganized printing pattern with low printing quality. To figure out the connection between the printing quality and the printing parameters, in our previous study (Qu et al., 2021), we have developed a computational fluid dynamics (CFD) model based on initial bubble model to quantitatively predict the jet flow development in the LIFT printing, the whole jet development process, including the bubble expansion process, bubble collapse process and jet generation process can be quantitatively predicted. The model was validated by the experimental results, parametric study was conducted to determine the appropriate printing parameters based on this CFD model, the simulation results were used to modify the operating parameters in the later experiments, such as input laser pulse energy and the bioink layer thickness, then a better printing quality was achieved. Then, a well-organized pattern with alphabets &ldguo;UT-CUMT&rdguo; based on the chosen printing parameters was successfully printed. Figure 2 shows the comparison between the simulation results and the optimized printing droplet based on this CFD model.

Liquid transfer for different EAL cases; optical microscope image of the hole in graphene EAL after LIFT printing (Note: Yellow dash lines are the bottom boundary of sodium alginate hydrogel layer)

Figure 2. Liquid transfer for different EAL cases; optical microscope image of the hole in graphene EAL after LIFT printing (Note: Yellow dash lines are the bottom boundary of sodium alginate hydrogel layer)

To further explore the effect of EAL materials on the jet formation in LIFT process, in our recent research (Zhou et al., 2022), we experimentally compared the performances of three materials (gold, gelatin, and graphene) as the EAL for low energy absorption rate bioink (sodium alginate solution) in the LIFT printing. As shown in Fig. 3, it was found that the EAL greatly influences the bubble and jet generation process in the LIFT printing. In the first case when no EAL was applied, no jet was formed but the deformation of bioink layer was observed. This implies that the absorbed energy from the laser using pure bioink was not enough to generate a bubble and support the development of bubble in order to form a jet. Therefore, to enhance the energy absorption EAL was adopted, we studied three different EAL materials, gelatin, graphene and gold, and each of them was coated on the donor slide. From Fig. 3, we can conclude that with the adoption of EAL stable jet can be formed using graphene EAL due to its larger laser energy absorption in the infrared range, but gelatin and gold EALs could not form a jet flow due to its selective absorption other than in the infrared range. Furthermore, from the microscope images of EAL after the LIFT process, we found significant mechanical impact signs on the EAL, this indicates that in LIFT cases with EAL, besides the heat effect, the mechanical impact may also bring an initial momentum to the bubble, which may further influence the bubble collapse and jet formation process.

Optimized LIFT droplet printing based on CFD model (Qu, et al., 2021)

Figure 3. Optimized LIFT droplet printing based on CFD model (Qu, et al., 2021)

LIFT bioprinting is a technology with amazing potentials in the next generation of biomedical engineering and tissue engineering, we are trying to figure out all associated mechanisms from the bubble generation to jet development process from thermofluids perspective, outcomes in our studies are expected to provide design strategies for optimizing the laser assisted bioprinting technology, thereby making a significant impact on the recent fast-developing bioprinting and biofabrication.

REFERENCES

Ozbolat, I.T. (2015) Bioprinting Scale-Up Tissue and Organ Constructs for Transplantation, Trends Biotechnol., 33: 395–400.

Murphy, S.V. and Atala, A. (2014) 3D Bioprinting of Tissues and Organs, Nat. Biotechnol., 32: 773–785.

Koch, L. et al. (2010) Laser Printing of Skin Cells and Human Stem Cells, Tissue Eng. – Part C Methods, 16: 847–854.

Morales, M., Munoz-Martin, D., Marquez, A., Lauzurica, S., and Molpeceres, C. (2017) Laser-Induced Forward Transfer Techniques and Applications, Advances in Laser Materials Processing: Technology, Research and Applications, Elsevier Ltd. DOI: 10.1016/B978-0-08-101252-9.00013-3

Antoshin, A.A. et al. (2019) LIFT-Bioprinting, Is It Worth It? Bioprinting, 15: e00052.

Pirlo, R.K., Wu, P., Liu, J., and Ringeisen, B. (2012) PLGA/Hydrogel Biopapers as a Stackable Substrate for Printing HUVEC Networks via BioLP™, Biotechnol. Bioeng., 109: 262–273.

Riester, D., Budde, J., Gach, C., Gillner, A., and Wehner, M. (2016) High Speed Photography of Laser Induced forward Transfer (LIFT) of Single and Double-Layered Transfer Layers for Single Cell Transfer, J. Laser Micro Nanoeng., 11: 199–203.

Smausz, T., Hopp, B., Kecskeméti, G., and Bor, Z. (2006) Study on Metal Microparticle Content of the Material Transferred with Absorbing Film Assisted Laser Induced Forward Transfer when Using Silver Absorbing Layer, Appl. Surf. Sci.: 252, 4738–4742.

Sorkio, A. et al. (2018) Human Stem Cell Based Corneal Tissue Mimicking Structures Using Laser-Assisted 3D Bioprinting and Functional Bioinks, Biomaterials, 171: 57–71.

Gruene, M. et al. (2011) Laser Printing of Three-Dimensional Multicellular Arrays for Studies of Cell-Cell and Cell-Environment Interactions, Tissue Eng. – Part C Methods, 17: 973–982.

Dias, A.D., Unser, A.M., Xie, Y., Chrisey, D.B., and Corr, D.T. (2014) Generating Size-Controlled Embryoid Bodies Using Laser Direct-Write, Biofabrication, 6.

Xiong, R., Zhang, Z., Chai, W., Chrisey, D.B., and Huang, Y. (2017) Study of Gelatin as an Effective Energy Absorbing Layer for Laser Bioprinting, Biofabrication, 9.

Qu, J. et al. (2021) Printing Quality Improvement for Laser-Induced forward Transfer Bioprinting: Numerical Modeling and Experimental Validation, Phys. Fluids, 33.

Dou, C. et al. (2021) A State-of-the-Art Review of Laser-Assisted Bioprinting and Its Future Research Trends, ChemBioEng Rev., 8: 517–534.

Zhou, S. , Li, J., and Xu, B. (2022). Study of the Graphene Energy Absorbing Layer and the Viscosity of Sodium Alginate in Laser-Induced-Forward-Transfer (LIFT) Bioprinting, in ASME 2022 International Mechanical Engineering Congress & Exposition (IMECE), Columbus, OH.

参考文献

  1. Ozbolat, I.T. (2015) Bioprinting Scale-Up Tissue and Organ Constructs for Transplantation, Trends Biotechnol., 33: 395–400.
  2. Murphy, S.V. and Atala, A. (2014) 3D Bioprinting of Tissues and Organs, Nat. Biotechnol., 32: 773–785.
  3. Koch, L. et al. (2010) Laser Printing of Skin Cells and Human Stem Cells, Tissue Eng. – Part C Methods, 16: 847–854.
  4. Morales, M., Munoz-Martin, D., Marquez, A., Lauzurica, S., and Molpeceres, C. (2017) Laser-Induced Forward Transfer Techniques and Applications, Advances in Laser Materials Processing: Technology, Research and Applications, Elsevier Ltd. DOI: 10.1016/B978-0-08-101252-9.00013-3
  5. Antoshin, A.A. et al. (2019) LIFT-Bioprinting, Is It Worth It? Bioprinting, 15: e00052.
  6. Pirlo, R.K., Wu, P., Liu, J., and Ringeisen, B. (2012) PLGA/Hydrogel Biopapers as a Stackable Substrate for Printing HUVEC Networks via BioLP™, Biotechnol. Bioeng., 109: 262–273.
  7. Riester, D., Budde, J., Gach, C., Gillner, A., and Wehner, M. (2016) High Speed Photography of Laser Induced forward Transfer (LIFT) of Single and Double-Layered Transfer Layers for Single Cell Transfer, J. Laser Micro Nanoeng., 11: 199–203.
  8. Smausz, T., Hopp, B., Kecskeméti, G., and Bor, Z. (2006) Study on Metal Microparticle Content of the Material Transferred with Absorbing Film Assisted Laser Induced Forward Transfer when Using Silver Absorbing Layer, Appl. Surf. Sci.: 252, 4738–4742.
  9. Sorkio, A. et al. (2018) Human Stem Cell Based Corneal Tissue Mimicking Structures Using Laser-Assisted 3D Bioprinting and Functional Bioinks, Biomaterials, 171: 57–71.
  10. Gruene, M. et al. (2011) Laser Printing of Three-Dimensional Multicellular Arrays for Studies of Cell-Cell and Cell-Environment Interactions, Tissue Eng. – Part C Methods, 17: 973–982.
  11. Dias, A.D., Unser, A.M., Xie, Y., Chrisey, D.B., and Corr, D.T. (2014) Generating Size-Controlled Embryoid Bodies Using Laser Direct-Write, Biofabrication, 6.
  12. Xiong, R., Zhang, Z., Chai, W., Chrisey, D.B., and Huang, Y. (2017) Study of Gelatin as an Effective Energy Absorbing Layer for Laser Bioprinting, Biofabrication, 9.
  13. Qu, J. et al. (2021) Printing Quality Improvement for Laser-Induced forward Transfer Bioprinting: Numerical Modeling and Experimental Validation, Phys. Fluids, 33.
  14. Dou, C. et al. (2021) A State-of-the-Art Review of Laser-Assisted Bioprinting and Its Future Research Trends, ChemBioEng Rev., 8: 517–534.
  15. Zhou, S. , Li, J., and Xu, B. (2022). Study of the Graphene Energy Absorbing Layer and the Viscosity of Sodium Alginate in Laser-Induced-Forward-Transfer (LIFT) Bioprinting, in ASME 2022 International Mechanical Engineering Congress & Exposition (IMECE), Columbus, OH.
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