Page 210 - IJB-9-2

International Journal of Bioprinting Three-dimensional bioprinting in toxicological research

devices. Several studies declare that these techniques could
produce spheroid within 24 – 72 h .
[56]
Several papers accentuate the important role of spheroids
in toxicology studies. Penzes et al. examined the toxic effect
of primycin-sulfate in 2D and 3D HepG2 and hNHEPSco-
cultured with fibroblasts in 1:4 ratio. They used V-shaped
plates to form aggregates within 24 h and observed that the
level of primycin-sulfate induced cell death was lower than in
2D cultures. Furthermore, the non-toxic level of primycin-
sulfate treatment resulted in an increased expression of
IL-11 and IL-24 . Bell et al. used ultra-low attachment
[57]
plates to create spheroids from primary human hepatocytes
and observed that the spheroids are suitable for modeling
of drug-induced liver injury (DILI). They found that bile
acid accumulated on chlorpromazine treatment and viral
infection enhanced trovafloxacin-induced toxicity .
[37]
Figure 3. The micropatterned co-cultures. In these co-cultures, the 7. Organoid
hepatocytes placed in individual islets on a plate, and then fibroblasts
or endothelial cells were seeded around them. Image created with An organoid is “a collection of organ-specific cell types
BioRender.com. that develops from stem cells or organ progenitors and
self-organizes through cell sorting and spatially restricted
6. Spheroids lineage commitment in a manner similar to in vivo” [58,59] .
Spheroids are 3D spherical cellular aggregates in which a Studying the development and the diseases of human
cell-cell interaction is formed, permitting the observation organs using in vivo experiments is challenging due to the
of their morphology and polarity. It is known that in significant interspecies differences between animal models
spheroids made of the HepG2/C3A cell line, a canaliculi- and humans. A better understanding of the biological role
like structure can be observed and bile acid production is of extracellular matrix and mapping of the regulation of
detectable too [44,45] . Spheroids could be generated in both signaling pathways in the microenvironment of stem cells
scaffold-based and scaffold-free ways, but the structure is have been made possible in the development of organoid
divided into three shells in each case. The outer shell is the culture systems. The terms of organoid include a wide
proliferation zone where the cell proliferation potential range of different systems, but Fatehullah et al. set forth
is the highest; the quiescent zone is located at the inner the most accurate definition of the term so far; they define
side where the cells are at rest; and the innermost side, “an organoid as an in vitro 3D cellular cluster derived
the core, has a zone of necrotizing cells because nutrients exclusively from primary tissue, embryonic stem cells,
and oxygen cannot reach there. Their maintenance of or induced pluripotent stem cells (iPSC), capable of self-
spheroids is simple, and they can be generated from renewal and self-organization and exhibiting similar organ
many cell types. Spheroids are involved in many drug functionality as the tissue of origin” .
[60]
development methods, especially tumor spheroids In the human body, cells are present in a highly
used in cancer research, which offer more insights into complex microenvironment, and many synchronized
tumor biology due to their biosimilarity to solid tumors signaling interactions result in a proper development,
in vivo with regard to cell morphology, proliferation, regulation, and maintenance of cell phenotype and
oxygenation, nutrient uptake, waste excretion, and function. Furthermore, cells in tissues are affected by
drug uptake. Since the geometric localization of cells is signaling effector molecules, nutrients, and waste products
crucial for proper function, the spheroid models can be along different concentration gradients. This phenomenon
applied in toxicology tests, so they can serve as suitable is mimicked by some 3D culture systems where cells are
pharmacological tools [38,46-55] .
at the center of an aggregate or organoid and they have
Spheroids can be produced in different ways, such less access to media factors, as opposed to 2D systems.
as using of ultra-low attachment plates, hanging drop The development of physiological, biochemical, and
technique, magnetic levitation and magnetic 3D printing, biomechanical microenvironments by 3D techniques
spinner flasks, matrix encapsulation, matrix-on top and can affect cell proliferation, differentiation, cell survival,
matrix embedding, microcarriers beads, and microfluidic morphogenesis, cell migration, and mechano-reactions.

Volume 9 Issue 2 (2023) 202 https://doi.org/10.18063/ijb.v9i2.663