Page 127 - IJB-10-6

International Journal of Bioprinting Fluid mechanics of extrusion bioprinting

Figure 2. Different flow regimes for a fluid issuing from a nozzle with (A) We < 1, (B) We ≈ 1 , and (C) We > 1, where the interval between consecutive
52
frames at (A) and (B) is ∆t = 5 ms. Abbreviations: We, Weber number; ∆t: time interval between consecutive images. Adapted with permission from ref.
Copyright © 2009 Cambridge University Press.

The velocity of a filament at the outlet of the nozzle the flowing solution, leading to deformations in the cell
is controlled by the extrusion pressure or the piston/ membrane and further impacting cell viability and stability
screw linear/angular velocity. The difference between the after printing. 36,61,62
filament velocity (U ) and printing head horizontal-moving A study on cell viability in pneumatic and screw-
34
s
speed (U ) affects the diameter of the printed filament. driven bioprinting processes indicate that despite the
p
Theoretically, if these velocities are equal, the diameter of higher accuracy of screw-driven bioprinting, it can result
the filament will be the same as that of the nozzle. If U >
p
U , the filament will be stretched during printing, resulting in a higher percentage of cell damage in comparison
with pneumatic bioprinting. Nevertheless, stresses inside
s
in thinner or even discontinuous filament deposition. the nozzle play a primary role in the survivability and
When U < U , a thicker filament and material bulge are
s
p
formed at the front edge of the needle. 36 viability of cells during the extrusion printing process.
These stresses originate from the velocity gradients in
2.3 Cell viability in extrusion bioprinting the bioink flowing through the nozzle that deform the
Printing of a cell-laden fiber involves the transmission of cells. The extent of cell injury depends on the magnitude
thermal and mechanical energy from the printing head and duration of the applied stresses. Typically, cells can
63
to the bioink, which can influence the cell phenotype endure stresses to a certain extent through adaptation
and viability (e.g., by interacting with DNA), damage mechanisms; nonetheless, if the stresses exceed the cell’s
cell membrane, or alter the osmotic equilibrium between capacity to withstand them, irreversible damage can
cells and the environment. The primary damage to occur, resulting in cell death. 64,65 High shear stress is one
60
cells occurs due to the force or stresses induced within of the most detrimental factors that reduces cell viability
Volume 10 Issue 6 (2024) 119 doi: 10.36922/ijb.3973