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International Journal of Bioprinting Review of 3D bioprinted organoids

Figure 2. Bioinks for stem cell and organoid bioprinting. (A) Oxidized alginate and ADSCs for bioprinting as bioinks. Reprinted with permission from
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[36]
ref. . Copyright 2014 Elsevier. (B) Gel-UPy-Tyr bioink for extrusion bioprinting. Reprinted with permission from ref. . Copyright IOP Publishing. (C)
hMSCs activity in printed bioinks, 0% PEGDMA (10% GelMA + 1.25% alginate + 0% PEGDMA + 3% gum), Gum (10% GelMA + 1.25% alginate + 2%
PEGDMA + 3% gum), M-Gum (10% GelMA + 1.25% alginate + 2% PEGDMA + 3% crosslinked gum). Reprinted with permission from [39] . Copyright
2022 Elsevier. (D) hASCs live and dead staining in KEGC mixed bioink printed showed that living cells were stained green, with a high cell survival rate
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and good migration ability. Reprinted with permission from . Copyright 2023 ACS Publications. (E) Preparation of intestinal organoids and submucosal
cell co-culture system using bioprinting and dECM bioink (from ref. licensed under Creative Commons Attribution 4.0 license). (F) Bioprinting using
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SF-dECM bioinks and BMSCs activity in print structures measured by CCK-8. Reprinted with permission from ref. . Copyright 2023 Elsevier.
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other bioprinting technologies . Reducing the size of the suspension medium, which deposits bioink in a support
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nozzle is an effective method to improve the resolution. bath containing the suspension medium. A suspension
However, the decrease in the size of the nozzle is prone medium is a yield stress material, showing solid and liquid
to blockage and increases the extrusion pressure, which properties according to the critical stress. When no external
leads to a decrease in cell survival rate. Therefore, when force is applied, the suspended medium behaves like a
using extrusion-based bioprinting technology, appropriate solid under critical stress. When the printing nozzle moves
parameters should be set in combination with multiple in the suspended medium, the generated force exceeds
factors such as viscosity, printability, and cell survival the critical stress, above which the suspended medium
rate of bioink . In light of this, developing new EBB flows like a liquid. When the nozzle passes through, the
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technologies can effectively improve the areas where the suspended medium quickly returns to the solid form
limitations of traditional EBB technologies are found. in a self-healing manner [56,57] . The characteristics of the
suspended medium support the printing of low-viscosity
The shear stress generated by the extrusion of bioinks bioink, maintain the stability of the printing structure,
with low viscosity is minor and will not significantly impact and realize all-around printing, free from the constraints
cell activity, but the complex organizational structure of construction direction, complex geometric shape, and
cannot be firmly maintained after printing . Suspension other factors . Lee et al. developed a freeform reversible
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bioprinting (also known as embedded bioprinting) enables embedded suspended hydrogel (FRESH) technology, which
the printing of low-viscosity bioinks that effectively uses gelatin particles as the suspension medium to support
improve cell survival. Unlike the traditional extrusion the printing process. When heated to 37°C, the suspension
printing method, which deposits bioink in cylindrical medium will melt and release the printed structure .
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silk on a flat surface, suspension printing introduces a Using collagen as bioink and human embryonic stem cell-

Volume 9 Issue 6 (2023) 80 https://doi.org/10.36922/ijb.0112