Page 91 - IJB-9-6

International Journal of Bioprinting Review of 3D bioprinted organoids

derived cardiomyocytes (hESC-CMs), they achieved high- spatter is inevitable in the injection process, leading to the
resolution bioprinting of cardiac organoids with systolic decline of resolution . In addition, due to the limitation
[64]
function using FRESH technology. Suspension bioprinting of nozzle size, inkjet bioprinting is only suitable for bioinks
also has some limitations . The first limitation is that the with low viscosity and cell density. Otherwise, the nozzle
[59]
integrity of the printing structure may be compromised blockage is likely to happen during the printing process,
when the structure is extracted from the suspended resulting in poor durability of the print head .
[63]
medium. The second limitation is that the suspended LAB techniques, including laser-guided direct writing
medium restricts the printing process. For example, the (LGDW) and laser-induced forward transfer (LIFT), are
bioink cannot be bioprinted at the temperature that the more commonly used due to their excellent performance.
suspended medium cannot accommodate. The LIFT device for bioprinting consists of three parts:
In addition, the research proves that mixed printing A laser source (mainly nanosecond laser), a target plate,
with other bioprinting technologies was also an effective and a receiving substrate. The target plate consists of clear
measure to improve the limitations of traditional EBB glass, an absorbing layer (made of metal), and a bioink
technology. Yeo et al. developed a hybrid bioprinting layer. The laser energy vaporizes the absorbing layer of
technology combining traditional EBB technology and metal to produce high-pressure bubbles that squeeze the
electrohydrodynamic jetting. Human adipose stem cells in bioink out as droplets. The absorbent layer can also avoid
the cell load structure printed by this technology could still direct contact between the bioink and the laser, protecting
maintain high cell vitality. It has been confirmed that the it from the laser . LIFT has significant advantages over
[65]
hybrid bioprinting technique can achieve rapid and stable inkjet bioprinting, as it is a nozzle-free printing method
bioprinting of cell-loaded structures without loss of cell hence no nozzle clogging problem, making it suitable for
viability . printing bioinks with high viscosity and cell density, with a
[60]
resolution of up to micron, 95% cell viability after printing,
2.2.2. Droplet‑based bioprinting and normal cell proliferation . Sorkio et al. used LIFT
[66]
Droplet-based bioprinting (DBB) technology is printed technology to print limbal epithelial stem cells (hESC-
by stacking independently separated droplets with LESC) and hASCs derived from human embryonic stem
higher resolution than EBB’s technology. According to cells to simulate natural corneal tissue structure, and the
the different principles of droplet formation, bioprinting cells maintained good vitality after printing . However,
[30]
technology can be divided into inkjet bioprinting, laser- LAB still has limitations despite its advantages over others.
assisted bioprinting (LAB), electrohydraulic dynamic jet The vaporization of the metal absorption layer may lead
(EHDJ) bioprinting, acoustic bioprinting, and microvalve to metal residue in the structure of bioprinting, causing
bioprinting. Among these, inkjet bioprinting and LAB are pollution. In addition, it is necessary to manufacture
currently more widely used. multiple target plates when printing multiple bioinks,

Inkjet bioprinting, in which bioink is ejected as a necessitating longer manufacturing time and higher
[67]
droplet from a nozzle when a pressure pulse is generated, cost .
may contain multiple print heads, each equipped with a 2.2.3. Photocuring‑based bioprinting
fluid chamber containing bioink and one or more nozzles Photocuring-based bioprinting uses light to solidify
with a minimum diameter of 18 µm. According to the bioinks. The technique can be subdivided into
driving mechanism of the pressure pulse, inkjet bioprinting stereolithography (SLA) and digital light processing (DLP)
can also be subdivided into thermal inkjet, piezoelectric according to different ways of curing.
inkjet, and electrostatic inkjet . Inkjet bioprinting has
[61]
good performance, based on: Firstly, it can generate SLA uses a UV point light source and point-to-point
droplets at a high-speed rate (up to 30 kHz), and the size irradiation of bioinks to cure layer by layer selectively and
of the droplets generated is tiny, resulting in a very high eventually form complex structures . SLA has no nozzle
[68]
resolution (about 50 µm). Secondly, inkjet bioprinting has limitation compared to extrusion-based bioprinting
good cell activity, and the cell survival rate is generally 80% technology, so it has higher resolution (generally less than
to 95% . As inkjet bioprinting is a non-contact printing 100 µm) and cell viability (up to 85%). It should be noted
[62]
technique, the droplets are not subjected to any harm by that UV light sources may cause damage to cells during
the print head moving after injection. Additionally, inkjet the printing process, resulting in reduced cell viability .
[69]
bioprinting has a print head with multiple nozzles that Grix et al. used SLA technology combined with HepaRG
can print multiple bioinks simultaneously, enabling the and human stellate cells and successfully achieved accurate
creation of multicellular tissues or organs . Nevertheless, bioprinting of liver organoids. The printed liver tissue
[63]
inkjet bioprinting has significant limitations. First, droplet equivalent was found to maintain cell viability for at least

Volume 9 Issue 6 (2023) 83 https://doi.org/10.36922/ijb.0112