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Applications of 3D bioprinted iPSCs
in a spatially controlled layer-by-layer fashion drugs, and scaffolds. Droplet-based bioprinting
precisely to biofabricate 3D tissue constructs. is derived from inkjet printing technology. It has
Extrusion printing permits printing of cell-dense been noted as a prominent technique widely used
high viscous hydrogels, but cells may experience in regenerative medicine to print cells due to its
high shear force stress during the printing process. flexibility. The droplet-based bioprinting can be
All three germ layers , neural tissues , cortical subdivided into inkjet, acoustic, and micro-valve
[66]
[67]
neural constructs , chondrocytes , cardiac bioprinting modalities. The drawback of using
[69]
[68]
tissue, and peripheral blood mononuclear cells this technology is that the rage of biomaterials
[70]
have been bioprinted from iPSC or iPSC derived compatible for this method of bioprinting is
cells using extrusion method. limited . A valve-based bioprinting method is
[77]
SLA and digital light projection (DLP) are used to print iPSCs differentiated post-printing
popular nozzle-free bioprinting techniques work into hepatocyte-like cells (HLC cells). A 40-layer
through photopolymerization. The liquid resin thick alginate bioink containing HLC cells
is solidified by UV laser beam in SLA. The showed typical liver tissue structure and the
DLP uses visible light for polymerization of the construct secreted hepatic albumin throughout
resin [71,72] . There are two types of SLA and DLP, the differentiation protocol. The work proved that
i.e., bottom-up and top-down approach. The layer the valve-based printing process is safe to print
of resin on a support platform is cured by a light human iPSCs by maintaining pluripotency and
from above in bottom-up biofabrication, while the differentiation .
[19]
light source is located under a transparent platform The laser-assisted bioprinting uses pulsed laser
in the top-down fabrication. iPSC-derived 3D beam with a focusing device. It consists of an
liver models which mimic the native liver module energy-absorbing layer coated with further layers
architecture were printed using this technique . of cell-encapsulated hydrogel. It is a nozzle-free
[73]
The flipside of SLA is that, it can be detrimental to bioprinting method that excludes clogging during
the living cells by damaging the genetic materials printing . Human iPSCs combined with bioinks
[78]
due to the use of UV. Moreover, the use of photo- were bioprinted with laser-assisted bioprinting
initiator resins may be cytotoxic to the cells . Vat method and the cells were evaluated for their
[74]
polymerization (VP) based bioprinting is a novel efficacy, pluripotency, and differentiation capacity.
and accurate bioprinting method tissue engineering The hyaluronic acid-based bioinks are ideal for
applications . Various types of photo-initiators laser-assisted bioprinting [16,79] . While designing
[75]
are used for the cross-linking of the printed tissues a tissue structure for bioprinting, factors such as
in the VP based bioprinting. VP use light sensitive shape, size, resolution, scaffold materials, iPSCs,
hydrogels such as polyethylene glycol–diacrylate or iPSC derived cellular components, and post-
(PEGDA) and gelatin-methylacryloyl (GelMA). processing tissue dynamics are to be considered.
Label-free diamagnetophoretic printing is another Bioprinting can be carried out as direct printing,
method for microtissue printing uses intrinsic crosslinking during the bioprinting, post-printing
diamagnetic forces to control positioning of cells crosslinking, and hybrid methods, where more
in a paramagnetic medium. Magnetic bioprinting than one technique is used for printing the final
is a contactless technique which does not use tissue construct. The factors appear to affect
nozzles and therefore promise less contamination cell survival after bioprinting are shear stress,
of cell suspension. Whole blood cells were printed laser exposure, duration, temperature, humidity,
using this technique , this technique may be mechanical pressure, and vibration of the printing
[76]
efficient to adopt to print iPSCs as there is fewer process. The selection of the printing techniques
chemical manipulations that are involved. depends on the end use of the printed tissues, such
Droplet-based bioprinting is simple, fast, and as organ/tissue transplantation, disease modeling,
precisely controlled bioprinting method to deposit or drug evaluation. Among, all the methods
composites of cells, growth factors, biomolecules, mentioned, extrusion bioprinting is the most
64 International Journal of Bioprinting (2020)–Volume 6, Issue 4
