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International Journal of Bioprinting dECM bioink for in vitro disease modeling

guidelines for the preparation of dECMs for use in clinical complex tissue structures in conjunction with dECMs. For
study, covering topics such as biocompatibility, viruses, example, Pluronic F-127 (PF-127) is a type of hydrophilic
and bacterium, should be discussed. detergent material that forms a solid gel structure at 37°C
but forms a liquid below the gel point. It can be washed
2.4.2. Fabrication issue of dECM bioink with water or a medium and thus can be applied to form
Different tissues and organs in the human body have a sacrificial structure, such as the hollow structure of a
different mechanical properties. For example, the brain vessel. Gao et al. developed vascular models based on
and other soft tissue have low mechanical stiffness, a vascular dECM together with calcium-PF-127 (CPF-
whereas the bone has high mechanical stiffness. Cells also 127). The usage of CPF-127 allowed the formation of
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exhibit different behaviors, including differentiation and a hollow structure, and by regulating the printing speed,
proliferation, depending on the stiffness of the cultured atherosclerotic models were developed to study the
substrate. Therefore, simulation of specific mechanical vascular disease pathologies. As such, incorporation
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properties in biomaterial for recapitulating native tissue is with supportive biomaterial can improve not only the
essential for predicting cellular behavior and fabricating mechanical properties of the printed structure but also
artificial tissue models. One of the advantages of dECM the fabrication freedom for the complex structure.
bioinks is that their mechanical properties can be changed
by adjusting the concentration of dried dECM; however, 3. Decellularization and evaluation
the adjustability of mechanical properties by changing
the dECM concentration is limited owing to the solubility methodologies
of the dECM. In addition, with a low-viscosity dECM Decellularization is an important procedure for clearing
bioink, it is difficult to maintain the structure during cellular components from the tissue while preserving
the fabrication process, whereas a high-viscosity bioink only the ECM. The decellularization method needs
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can induce nozzle clogging in 3D bioprinting and affect to be optimized depending on the tissue and organ,
the cell growth and morphology. Thus, it is necessary to because mechanical stiffness and protein compositions
adjust the mechanical properties of the dECM so that vary between tissues. This section introduces different
it has similar stiffness to native tissue with sufficient decellularization approaches and the optimization steps
printability. Currently, various supporting materials have for specific tissues, as well as methods for evaluating the
been adapted to overcome mechanical weakness, 102,103 acquired dECMs.
including gelatin methacryloyl (GelMA), poly(ethylene
glycol)-diacrylate (PEG-DA), vitamin B2, and other 3.1. Physical treatment
crosslinkers, which induce rapid crosslinking under The purpose of physical treatment in decellularization
external stimuli such as light or chemical treatment. With is to destroy cellular membranes and achieve cellular
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supporting crosslinkers, the tuned mechanical properties dissolution. Physical treatment is available in different
allow free fabrication before crosslinking, which can forms, including chopping, repeated freeze–thaw
prevent nozzle clogging in the 3D printer and reduce cycles, and sonication. The conditions of these physical
the shear-stress effect on cellular viability. In addition, treatments should be adapted differently according to
it is favorable to recapitulate the stiffness of native tissue tissue characteristics. For example, in the case of extremely
after crosslinking. For example, a spinal cord-derived soft tissues (e.g., the brain and peripheral nerves), the inner
dECM is conducive for neural stem cell adhesion and structure of the ECM could be destroyed if the tissues are
differentiation; however, it is easily degradable and chopped into excessively small pieces. 108,109 In the case
thus requires mechanical-property tailoring. He et al. of retina, the ECM ultrastructure can be damaged in
developed a spinal cord dECM with GelMA to tune and freeze–thaw processes because of ice crystal growth. 110,111
support the mechanical properties until neural stem Conversely, cartilage and bone decellularization requires
cells were sufficiently differentiated. In addition to mechanical destruction to generate small pieces, such
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GelMA, biocompatible polymers such as PEG-DA can that the cellular membrane can be destroyed and the cells
be applied to regulate the mechanical properties. Shin removed from the tissue. 112,113 Therefore, a suitable physical
et al. developed a PEG-DA-incorporated cardiac dECM treatment is essential in pre-treatments for decellularization
to recapitulate the moduli of cardiac tissues. They found to effectively remove cellular components and maintain
that the compressive modulus of PEG-DA/dECM could the ultrastructure of the tissue, depending on the density,
be tuned by regulating the concentration of PEG-DA. mechanical stiffness, and protein/lipid composition.
The enhanced bioink is favorable for maintaining the However, a single physical treatment is inadequate for
shape fidelity and adaptability of the printed construct. sufficiently cleaving the cellular components; therefore,
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Additionally, sacrificial materials allow the formation of a combination of physical and chemical treatments is

Volume 10 Issue 2 (2024) 139 doi: 10.36922/ijb.1970