Page 267 - IJB-10-4

International Journal of Bioprinting Cell viability in printing structured inks

pressure and shear stress during the printing process with lower average and maximum pressures, as well as average
this kind of structured inks. and maximum shear stress, compared to their conventional
Creating the vascular-like structure with the same cell counterparts. For instance, considering vascular-like inks
distribution using conventional printing would require with extruded fiber layer distances of 2:1:1, the average
smaller nozzles to achieve the same printing resolution. and maximum wall shear stress did not exceed 6.595e+0
Taking the example of cell distribution in the intermediary Pa and 2.069e+2 Pa, respectively. In contrast, conventional
and outer layers of the structured inks, 27G needles printing exhibited corresponding values of 3.046e+1 Pa
were used in conventional printing for comparison, as and 3.657e+4 Pa, respectively. These examples highlight
chosen in the simulation. Figure 14C shows viable and the potential of structured inks to mitigate fluid forces,
dead cells of fibers printed with the vascular-like ink in particularly in the context of tissue engineering.
longitudinal view, whereas Figure 14D depicts the control To further enhance cell viability, we introduced
group, demonstrating viable and dead cells in fibers equivalent analyses of fluid forces, focusing on commonly
printed using conventional printing. As shown in Figure used symmetric inks with different ink combinations, as
S21 (Supplementary File), cell viability in conventional well as core–shell inks with varying core layer radii. The
printing was significantly lower than that in structured equivalent analysis centered on the maximum shear stress
ink-based printing. The difference in viability was likely at the wall and at material phase interfaces. Validating the
primarily attributed to the different needle sizes, which reasonability of equivalent homogeneous inks was based
directly resulted in a significant difference in pressure on assessing average shear stress, considering minimal
and shear stress experienced by cells during the printing fluctuations in average and maximum pressures under
processes. Therefore, structured ink-based printing, which various structured parameters, along with comparable
enables direct printing of heterogeneous tissue structures, average shear stress at the wall and material phase
has an advantage in improving cell viability.
interfaces. For example, with a core layer radius of 2.8
The next stage of the work will focus on more in- mm in core–shell inks, the equivalent viscosity was 3.70
depth bioprinting experiments, initially emphasizing the Pa·s for cells in the flow domain of the shell layer, while
validation of cell viability via 3D printing of equivalent in the core layer, it was 1.72 Pa·s. We also found that the
homogeneous inks and, ultimately, refining the design of viscosity of equivalent homogeneous inks was positively
structured inks. Subsequently, a thorough comparative correlated with their experienced maximum and average
study on cell viability and the functional expression of shear stress, to some extent. Based on the simulation
cells in vitro will then be performed between structured results, the general workflow for structured ink design was
ink-based printing and conventional printing. The proposed, emphasizing considerations for cell viability.
experimental results will be compared with the simulated This workflow opens the door to a more efficient and
outcomes. The objective in later stages is to biofabricate cell-friendly method for structured ink-based printing.
functional tissues using structured inks, followed by in Furthermore, the simulation results were preliminarily
vivo animal experiments and clinical applications. validated by experiments using vascular-like ink-based
printing as an example, which demonstrated significantly
4. Conclusion enhanced cell viability compared to conventional printing.

This study presents a comprehensive exploration of fluid While the primary focus of fluid force analysis has
forces, examining maximum and average pressure, as centered on structured ink-based printing, this research
well as maximum and average shear stress, within the also contributes valuable insights into fluid forces in
context of structured ink-based 3D printing processes. conventional printing, paving the way for advancements in
The innovative application of this technology enables the printing materials and improved cell viability in the realm
bioprinting of tissue structures with significantly enhanced of 3D printing.
cell viability, surpassing the capabilities of conventional
printing methods.
Acknowledgments
By employing 18G needles for the proposed method
and their counterparts for conventional E3DP, we unveiled None.
the advantages of structured inks through quantitative Funding
analyses. These analyses encompassed 2-symmetric inks,
4-symmetric inks, vascular-like inks, and hepatic lobule This research is supported by the National Nature Science
analogue-like inks. Structured inks consistently exhibited Foundation of China (grant number 52275326).

Volume 10 Issue 4 (2024) 259 doi: 10.36922/ijb.2362