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International Journal of Bioprinting Simulation-based comparative analysis of nozzles for bioprinting

Figure 6. Maximum velocity (cm/s) of pneumatic and piston-driven simulations.
multiaxial needle, a velocity of 36.70 cm/s. They used a value of shear stress for all simulations is 455.43 Pa,
similar material mainly composed of alginate and also which are in both cases more than ten times lower than
fitted to the standard potential law, but their alginate bioink the threshold proposed by Blaeser et al. . In addition,
[38]
seems to be more viscous than ours. Nevertheless, their the shear stress distribution has little or no change over the
inlet was composed of three different needle entrances, simulation time, and a representation of the shear stress
and they set one velocity for each entrance (0.4, 1.81, and distribution can be seen in Figure 8. In this sense, the
6.57 cm/s). Therefore, similar to what happened in Reid shear stress distribution is much more concentrated in the
et al.’s experiment, results of Smith et al. are not directly tip of the nozzle than in the conical tip. This means that
comparable to ours due to these major differences in the cells are exposed to high shear stress for a longer time in
inlet. the conical tip than in the nozzle due to the difference in
geometry lengths, which may cause cell viability problems
3.3. Shear stress as described by Blaeser et al. . Thus, it can be concluded
[38]
Shear stress is the most important parameter to determine that both geometries generate a shear stress below what is
the cellular viability of any bioprinting process. Boularaoui reported as inappropriate for cells, and both can be used in
et al. and Blaeser et al. performed a thorough study these conditions for bioprinting.
[26]
[38]
of shear stress in bioprinting and both concluded that the
shear stress has a direct negative impact on the cellular In addition to Bleaser et al., other authors also studied
viability. Additionally, Blaeser et al. also determined that the shear stress for bioprinting purposes. Liu et al.
[38]
[39]
shear stress lower than 5 kPa might not have an important obtained low shear stress (30, 180, and 300 Pa) using
influence on cell survival. Figure 7 shows the shear stress different concentrations of a bioink with lower viscosity
and Figure 8 shows the shear stress distribution for all and using both needle and conical tips. Despite that they
simulations. We report the worst-case scenario, which used similar geometries, the different material and the
corresponds to the highest stress peak for each simulation. much lower inlet volumetric flow (1.67 mm /s) make
3
Bearing this in mind, the values of shear stress are 455.43 the comparison of results unfair. Müller et al. also
[55]
and 242.16 Pa for Nozzle and Cone pneumatic simulations, studied the shear stress using several needle and conical
respectively, and 362.85 and 383.24 Pa for Nozzle and Cone tips (namely 22, 23, 25, 27, and 30G) with a very similar
piston-driven simulations, respectively. Based on these alginate with nanocellulose bioink, obtaining results
results, the Nozzle geometry provokes higher shear stress around 160 Pa. Specifically, shear stress of the same 22G
than the Cone one in all cases. Nevertheless, the maximum conical tip geometry is 151.88 Pa. While this result is lower
difference is approximately 213 Pa and the maximum than any of our shear stress, they used 6 kPa, instead of

Volume 9 Issue 4 (2023) 216 https://doi.org/10.18063/ijb.730