Page 126 - IJB-10-6

International Journal of Bioprinting Fluid mechanics of extrusion bioprinting

Figure 1. Filament extrudability: (A) unextrudable (We ≈ 0), (B) discontinuous (We << 1) , (C) continuous yet uncontrollable (We < 1), and (D) continuous
~
and controllable (We > 1). Abbreviation: We, Weber number. The figure is prepared by authors using Microsoft Publisher.

due to Rayleigh-Plateau capillary instability 56–58 far from extrude. 40,41 In contrast, surface tension helps deposited
the nozzle (>20 Ri), this process does not disrupt the filaments maintain their shape and their cross-sectional
59
deposition of bioink in bioprinting, as the nozzle-stage profile. The wettability of a bioink, as measured by its
spacing is about 2Ri. The aforementioned flow regimes contact angle with a solid surface, governs the contact of
based on We can also occur due to a change in nozzle size. the first layer of the construct with the printing stage. A
Considering mass conservation, for a given flow rate of large contact angle improves the fidelity of the construct;
bioink, an increase in nozzle diameter will decrease We. conversely, a smaller contact angle helps secure the printed
construct to the printing stage, preventing undesired
The printability of a bioink is heavily influenced by deformations and movements during the printing process,
its surface tension and wettability. These properties play ultimately enhancing the structural integrity. Moreover,
36
a critical role in the formation of filaments during the ensuring sufficient wettability between the bioink and the
printing process. On one hand, a high surface tension nozzle can prevent problems, such as leaking, flooding, or
leads to smaller We at a given flow rate, causing poor wetting the exterior surface of the nozzle tip, as the bioink
extrudability with dripping extrusion or even failing to is extruded from the nozzle.
40

Volume 10 Issue 6 (2024) 118 doi: 10.36922/ijb.3973