Page 400 - IJB-9-4

International Journal of Bioprinting Impingement shear stress during microvalve-based bioprinting

Figure 7. Simulated droplet formation when it touches the building platform at different distances (H) between nozzle tip and platform, for upstream
pressure of (a) 0.6 bar and (b) 1.0 bar. The nozzle size was 300 µm in both simulations.

that at low upstream pressure, i.e., when a droplet with (Figures 7 and 8). Figure 7a and b presents a snapshot of the
a small ligament is forming, nozzle wall shear stress is moment that the droplet/jet lead point touches the platform
dominant (wall shear stresses ratio less than 1.0), while at at various H and for upstream pressure of 0.6 and 1.0 bar,
higher upstream pressure, i.e., when a jet is forming, the respectively. Considering the nozzle size of 300 µm, as H
platform shear stress exceeds the nozzle wall shear stress increased, the nozzle wall shear stress remained constant
and becomes dominant (wall shear stresses ratio more independent of H for two sample upstream pressures of
than 1.0). The rate of increase of wall shear stress ratio as 0.6 bar (Figure 8a) and 1.0 bar (Figure 8b). However, the
a function of upstream pressure was higher for the bigger impingement shear stress changed if H varied (Figure 8c
nozzle size, i.e., a linear functional fit to the data revealed and d). At low upstream pressure, increasing H from 0.3 to
a slope of 1.87 (R = 0.98) for 300-µm nozzle and a slope 3.6 mm resulted in a variation of impingement shear stress
2
of 0.43 (R = 0.97) for 150-µm nozzle (not presented in the between 3.73 and 6.01 kPa with maximum stress occurring
2
graphs). at H = 0.6 mm. At high upstream pressure, the same change
in H resulted in variation of impingement maximum shear
3.5. Effect of nozzle-to-platform distance (H) on stress of between 12.57 and 27.01 kPa, with its maximum
impingement shear stress predicted at H = 2.4 mm. The ratio of impingement shear
The simulation model was used to determine whether stress to the nozzle wall shear stress for both cases is
nozzle-to-platform distance plays a role in the ratio of plotted in Figure 8e and f, demonstrating that regardless of
impingement shear stress to nozzle wall shear stress the nozzle-to-platform distance, at low upstream pressure

Volume 9 Issue 4 (2023) 392 https://doi.org/10.18063/ijb.743