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International Journal of Bioprinting Exosome-based bioink for bioprinting

Figure 4. Bioink systems for printing. Reprinted with permission from ref. . Copyright 2019 Royal Society of Chemistry.
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cross-linked hydrogels and chemically cross-linked such as a limited cell survival rate and relatively low
hydrogels (Figure 4). The specific principles and examples resolutions .
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for hydrogel preparations can refer to the review by
Valot et al. . 3.2.2. Jetting-based bioprinting
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Inkjet bioprinting is derived from commercial two-
3.2. Printing methods dimensional (2D) inkjet printing technologies (Figure 5B).
There are several distinct available printing methods. Here, The main difference between this technology and
we briefly introduce three printing methods categorized extrusion-based bioprinting is that the bioink is produced
according to ASTM standards, which are extrusion-based, at a point where the nozzle head hits. Therefore, jetting-
jetting-based, and vat photopolymerization (VP)-based based bioprinting has the advantage of high resolution.
bioprinting. For jetting-based bioprinting, its bioink must be liquid-
like in case of blocking the nozzle. Besides, the viscosity
3.2.1. Extrusion-based bioprinting of biological ink is also difficult to control . Meanwhile,
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One of the most common bioprinting methods is the side effect brought by high resolution is slow printing
extrusion-based bioprinting (Figure 5A). It combines a speed. In addition, the discontinuous droplets can also
fluid distribution system and an automated robotic system. lead to a weak mechanical strength of the bioprinted
The fluid-dispensing system can be driven by a pneumatic-, structure . Therefore, it is recommended to adjust the
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mechanical-(piston or screw-driven), or solenoid-based mechanical properties of bioink to guarantee the printing
system . The working procedure of extrusion-based quality. For instance, Suntornnond et al. modified GelMA
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bioprinting includes three steps: (i) the hot-melt material through saponification and heat treatment, effectively
(as the bioink) is liquidized through the heater; (ii) the improving its printability and biocompatibility in thermal
bioink is pumped into filaments and sent to the hot-melt injection printing .
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nozzle; (iii) the nozzle head squeezes out of the bioink.
Through printing, CAD layered data can control the 3.2.3. Vat photopolymerization (VP)-based
path during the squeezing out of bioink and place it in bioprinting
the specified positions to solidify. The printed materials The working principle of VP-based bioprinting (laser-
can bond with the surrounding materials, stacking layer assisted bioprinting [LAB]) is that the laser focuses on the
by layer . Therefore, a stable bioink is needed for this glass plate absorption layer to produce a high-pressure
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approach. However, this technology has shortcomings, liquid foam and to push the cells to the acceptable

Volume 9 Issue 6 (2023) 115 https://doi.org/10.36922/ijb.0114