Page 136 - IJB-10-5

International Journal of Bioprinting Liver printing: from structure to application

biliary organoids. The hepatocyte-like cells could absorb duct structures to model alcohol-related liver disease
indocyanine green, accumulate lipids and glycogen, secrete (ALD) by co-culturing primary hepatocytes, hepatic
ALB and urea, and possess drug metabolism capabilities. sinusoidal endothelial cells, and stellate cells. Upon
Likewise, cholangiocytes exhibited γ-glutamyl transferase exposure to blood alcohol levels, the chip exhibited
activity and could store bile acids. Additionally, when ALD biomarkers, including lipid accumulation and
96
transplanted into immunodeficient mice, organoids could oxidative stress. Moreover, Ewart et al. conducted
survive for over 8 weeks. Currently, the main limitation tests on 870 liver chips based on the same design using
84
of organoids is the undefined growth environment, which 27 known drugs recommended by the Innovation and
leads to high variability and poor reproducibility, thereby Quality (IQ Consortium) with or without hepatotoxicity
75
restricting their clinical translation. Sorrentino et al. used and compared the results with 3D culture spheroids of
poly(ethylene glycol) (PEG) hydrogels incorporated with primary human hepatocytes. The findings indicated that
RGD peptides as a substitute for Matrigel in liver organoid liver chips exhibited higher accuracy, sensitivity, and
97
culture. The stiffness of this hydrogel was adjustable economic value. By constructing biomimetic liver lobule
and could be designed to match the stiffness of the liver chips to simulate the physicochemical microenvironment
(≈1.3 kPa). Compared to PEG hydrogels incorporating of the liver, it is possible to more accurately replicate liver
laminin, collagen IV, and fibronectin, the efficiency of disease models, extend cell culture time in vitro, and
organoid formation in PEG-RGD hydrogels was closer to facilitate testing for acute and chronic hepatotoxicity. 98,99
that in Matrigel, displaying similar morphology and gene Currently, the limitations of chips lie in their maintenance
expression patterns (Figure 4C and D). This study paves duration and the challenge of achieving substance and
85
the way for the future clinical application of organoids. information (signaling molecules) exchange between
multiple organs. 100,101
3.4. Liver-on-a-chip
Organ-on-a-chip is a microfluidic cell culture device 4. Bioprinting of liver tissue
where cells are cultured in continuously perfused 3D bioprinting technology generally refers to the
chambers. It is designed to mimic tissue- and organ- computer-assisted transfer process of patterning and
level physiological functions and replicate multicellular assembling biological and non-biological materials to
structures, tissue–tissue interfaces, physicochemical create bioengineered structures, according to specified
microenvironments, and vascular perfusion found 2D or 3D tissue designs. The advantage of 3D printing
in the human body. Organ-on-a-chip technology technology lies in its ability to simulate the structure and
86
holds great potential in various fields, such as tissue function of natural tissues through precise deposition and
development, organ physiology, disease modeling, and assembly of materials and cells, enabling spatiotemporal
drug screening. 87–92 Specifically in the liver, organ-on- control of cell–cell and cell–ECM communication for
a-chip technology supports the co-culture of multiple reconstructing tissue-like structures. This technology
liver cell types while incorporating vascular channels. has broad applications in tissue engineering, organ
This enables the establishment of liver disease models transplantation, drug screening, and other fields.
102
and the screening of hepatotoxic drugs. 93,94 Jang et al. Furthermore, compared to organ-on-chip and organoid
designed a liver-on-a-chip composed of rat, dog, or technologies, bioprinting can manufacture larger volumes
human hepatocytes, human liver sinusoidal endothelial (up to centimeters) and intricate tissue structures in
cells (LSECs), Kupffer cells, and hepatic stellate cells. vitro, achieving higher fidelity to physiological tissues.
The chip exhibited various hepatotoxicity phenotypes, Generally, the entire 3D bioprinting process can be divided
including hepatocyte injury, lipid accumulation, bile into three stages: (i) before printing, the design of the
stasis, and fibrosis, enabling the assessment of species- print is determined by obtaining the required anatomical
specific differences in drug metabolism and toxicity structures and dimensional information through imaging
95
(Figure 4E). Compared to traditional sandwich techniques (e.g., computed tomography [CT], magnetic
monoculture plates, this model is more sensitive in resonance imaging [MRI], X-ray) and defining the
detecting bosentan toxicity. Co-treatment of bosentan structure and dimensions of the print with computer-
(30 μM) with the bile salt export pump (BSEP) substrate aided design (CAD) software; (ii) the selection of bioink
cholyl-lysyl-fluorescein (CLF) inhibited CLF efflux, (cells, materials) and printing method (extrusion-based
leading to its intracellular accumulation in the liver bioprinting, photopolymerization-based bioprinting,
chip. This was consistent with the known mechanism of etc.) is made; and (iii) the printed structure is cultured
bosentan hepatotoxicity in humans (Figure 4F). Building and utilized for subsequent applications. Among these,
103
upon this work, Nawroth et al. established a liver organ- the most important aspects are determining the printing
on-a-chip with biomimetic hepatic sinusoids and bile method and selecting the bioink (Figure 5).

Volume 10 Issue 5 (2024) 128 doi: 10.36922/ijb.3819