Page 212 - IJB-9-6

International Journal of Bioprinting Multi-Cellular tissues/organoids manufacturing strategies

2.1. Jetting-based bioprinting speed, and layer thickness is essential to achieve improved
The mechanism of jetting-based bioprinting is the drop- outcomes. A couple of studies using extrusion-based
on-demand (DOD) patterning of bioink droplets onto bioprinting demonstrated the essential requirement of a
a substrate to create two-dimensional (2D) and 3D multi-cellular composition of the 3D liver model consisting
models, as shown in Figure 3A. This method relies on of hepatic parenchymal HepaRG cells, stellate cells (LX-2),
various mechanisms for generating and ejecting the and human umbilical vein endothelial cells (HUVECs), in
bioink droplets , such as the vaporization of bubbles order to construct a liver fibrogenesis model [38,39] . However,
[27]
by a heater in a thermal style , deformation under due to the complex cellular composition and multi-
[28]
electrode pressure in an electrostatic style , vibration scale spatial arrangement between cells and extracellular
[29]
of a piezoelectric actuator in a piezoelectric style [30,31] , or matrix in MTOs, the formulation of bioinks remains a
the application of high voltage field energy from nozzle challenge . The multi-cellular 3D bioprinting and bioink
[40]
electrodes in an electrohydrodynamic style [32,33] . As material design strategies proposed in the literature [40,41]
stated in Table 1, one of the advantages of jetting-based show great potential in the development of MTOs that
bioprinting is that it selectively ejects droplets when the mimic the native microenvironment of organs. However,
signal reaches the required levels, allowing for the precise this conceptual framework still relies on different types
formation of predetermined patterns. Moreover, due to of scaffolds, making it difficult to construct multi-tissue
the comparable size of the inkjet nozzle (50 μm) to that of organoids that truly reflect their physiological relevance.
a cell, it is also suitable for single-cell printing. The high- 2.3. Vat photopolymerization-based bioprinting
resolution printing capability facilitates the fabrication of Vat photopolymerization-based (VP-based) bioprinting
smaller tissues and organs, while the distinctive printing involves the creation of scaffold structures using
patterns promote enhanced interactions between cells photopolymerization reactions in which a photocurable
and the extracellular matrix . However, shear stress or liquid bioresin is exposed to the light of a specific
[34]
pressure during printing or collision with the substrate wavelength . The mechanism of VP-based bioprinting is
[26]
after ejection in jetting-based bioprinting may damage shown in Figure 3C. This technique encompasses various
the cell. Nonetheless, the proportion of cells affected methods such as stereolithography (SLA), digital light
by such damage is relatively low, and the efficiency and processing (DLP), and two-photon polymerization (2PP).
high-throughput capabilities of inkjet printing outweigh
its drawbacks. A novel method for creating multiple cell SLA utilizes laser refraction and scanning in a vat to
types and extracellular matrix tissue structures uses inkjet cure bioresin, with options for top-down or bottom-up
[26]
printing technology [35,36] . However, the studies highlight printing . It offers high resolution and the ability to print
the potential of inkjet technology for fabricating complex complex structures but has limitations due to harmful UV
hybrid tissue structures requiring multiple cell types. rays. As stated in Table 1, SLA techniques offer advantages
Further investigation is needed to optimize the printing such as high lateral and vertical printable resolution
parameters and analyze the stability and functionality of (around 20–50 μm and 25–100 μm, respectively), the
the printed tissues. ability to print a wide range of viscosities (up to 5 Pa·s),
high printable cell density (up to 10 cells per ml), and
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2.2. Extrusion-based bioprinting the potential to fabricate highly complex structures with
Extrusion-based bioprinting is a commonly employed support structures. On the other hand, DLP uses a digital
technique that allows for precise deposition of bioinks micromirror device to crosslink bioresin, allowing for
by extruding material from a nozzle . In general, the faster printing and large-scale structures with micron-
[37]
biomaterial can be extruded from cartridges using level resolutions . Lastly, the 2PP system employs a near-
[42]
either pneumatic pressure or mechanical forces, such as infrared femtosecond laser light source (around 740 nm
piston-driven or screw-driven mechanisms, as shown in wavelength) to fabricate microstructures with nanoscale
Figure 3B. Extrusion-based bioprinting allows for printing resolution (up to sub-100 nm) . The femtosecond laser
[43]
bioinks with high cell densities (10 –10 cells per ml) and is tightly focused on the bioresin using an oil-immersed
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the simultaneous deposition of multiple cell types to create objective lens. Polymerization in 2PP is initiated by
heterogeneous structures, as shown in Table 1. However, exciting molecules through two-photon absorption. This
this technique presents challenges related to cell viability process occurs rapidly (mm/seconds of scanning speed)
due to shear stress-induced damage and nozzle clogging. To and enables the fabrication of highly complex structures
enhance the performance of extrusion-based bioprinting, at any spatial position. However, the application of 2PP
optimization of bioink composition, selection of appropriate in bioprinting is limited by drawbacks such as material
nozzle size, and careful material choice are necessary. Prior degradation caused by high laser power and bubble
to printing, adjusting printing parameters such as pressure, damage . A manufacturing method for MTOs called
[43]

Volume 9 Issue 6 (2023) 204 https://doi.org/10.36922/ijb.0135