Page 254 - IJB-10-4

International Journal of Bioprinting Cell viability in printing structured inks

from 8.05e+2 Pa to 1.05e+3 Pa, with an increase in height. File). This similarity of average strain rate arises from
Conversely, in conventional printing using ink 1 and ink 2, identical volume flow rates at the inlet and corresponding
the average pressure at all cross-sectional positions exceeded cross-sectional positions, resulting in a similar trend of
2.70e+4 Pa and 3.0e+4 Pa, respectively. Notably, the average flow velocities. Correspondingly, the average strain rate in
and maximum pressures for all cross-sectional positions the domain phase 2, in 2-symmetric ink-based printing,
were significantly lower in structured inks compared to the increased from 3.70e-1 s⁻¹ to 8.22 s⁻¹. Under the condition
corresponding control group. of the same viscosity, the strain rate is proportional to

Regarding shear stress (Figure 4C and D), a decrease shear stress; therefore, shear stress at corresponding ink
in height led to an increase in both average and maximum positions exhibited a similar relationship. Regarding
shear stress. In 2-symmetric ink-based printing, for average pressure, the inlet pressure in 2-symmetric and
instance, at a cross-sectional height of 3.6 mm, the average 4-symmetric ink-based printing was 1.20e+3 Pa and
and maximum shear stress in phase 1 were 2.82e+1 Pa and 1.128e+3 Pa, respectively. The higher inlet pressure in
2.90e+1 Pa, respectively. In phase 2, these values increased 2-symmetric inks is attributed to the larger viscosity of this
39
to 3.00e+1 Pa and 3.10e+1 Pa, respectively. In 4-symmetric inks, while the flow velocity and nozzle remain the same.
ink-based printing, at a cross-sectional height of 3.6 mm, In conventional printing using ink 1 and ink 2, the inlet
the average and maximum shear stress were 2.76e+1 Pa pressures were 2.75e+4 Pa and 3.10e+4 Pa, respectively.
and 2.87e+1 Pa, respectively. In conventional printing The inlet pressure in the structured ink-based printing
with ink 1, at a height of 3.6 mm, the average shear stress group was significantly smaller than in the conventional
exceeded 6.30e+1 Pa, with corresponding maximum printing group (Figure 5C). This difference is largely due
shear stress reaching 7.10e+1 Pa. At other cross-sectional to the use of smaller nozzles in conventional printing.
positions, the average shear stress and maximum shear Given the outlet connection to the air, the pressure
stress for structured ink-based printing were comparable gradient from inlet to outlet is significantly lower in the
to those in conventional printing. However, it can be 2-symmetric and 4-symmetric ink groups compared to
inferred that as the selected height decreases further, their corresponding conventional groups, resulting in a
the differences in shear stress between conventional significant pressure difference.
and structured ink-based printing will become more
pronounced. Of note, the ratios of maximum pressure 3.2. Advantages of structured ink-based printing for
to fluid average pressure and maximum shear stress to vascular tissue engineering
average shear stress were consistently less than 1.03 and 1.2, A critical challenge in engineering large-scale tissues
respectively (Figure S5A and S5B in Supplementary File). is the efficient transport of oxygen and nutrients,
This indicates no significant differences in fluid pressure underscoring the significance of vascularization in tissue
and in shear stress. Given the emphasis of this study on engineering. Conventional E3DP of small-scale vascular
42
examining fluid forces of structured inks compared to structures often employs smaller nozzles to achieve higher
conventional inks, we postulate that fluid forces with resolution, a practice deemed detrimental to cells. Blood
2-symmetric and 4-symmetric inks are lower than those vessels, comprising endothelial cells, smooth muscle
10
for conventional printing. cells, and fibroblasts in inner, middle, and outer layers,
The variations in shear stress were analyzed using the respectively, served as the basis for study with structures
average strain rate at different cross-section positions, with layer distances of 2:1:1. 35,43 We compared fluid forces
as depicted in Figure 5A. This analysis was based on using structured ink-based printing and conventional
the contours of strain rate shown in Figures S4B and methods, specifically examining interactions between
S6 (Supplementary File). In the domain phase 1 using material phases. To determine ink structure parameters
2-symmetric ink-based printing, the strain rate gradually corresponding to specific layer distances, we considered
intensified as the height (relative to the outlet) decreased. cases involving identical biomaterial inks with varying
As the cross-sectional height decreased from 21.6 mm to cells loaded with corresponding material phases.
3.6 mm, the average strain rate increased from 3.89e-1 s⁻¹ Utilizing the bisection method, we evaluated the cross-
to 8.66 s⁻¹. In the domain using 4-symmetric ink-based sectional structures of fibers extruded at the nozzle outlet,
printing, the average strain rate increased from 5.79e- maintaining the defined ratio, by using vascular-like inks
1 s⁻¹ to 8.54 s⁻¹. In conventional printing using ink 1 and with different geometric parameters. Subsequently, we
ink 2, both the average strain rate increased from 3.25e- analyzed average and maximum pressures within nozzle
1 s⁻¹ to 1.96e+1 s⁻¹. Figure 5B presents the quantification domains for phase 1 and phase 2, as well as average and
of average velocities, calculated by the corresponding maximum shear stress at wall and material phase interfaces,
contours in Figure S4C and Figure S7 (Supplementary comparing results with conventional printing processes.

Volume 10 Issue 4 (2024) 246 doi: 10.36922/ijb.2362