Page 191 - IJB-9-1

International Journal of Bioprinting 3D bioprinting of tissue with carbon nanomaterials

on the back of the silicate glass, and a substrate receiver. The cell viability (>85%) without any shear force on the cells
focused laser beam on the metal film induces local heating are made possible through SLA bioprinting [25,26] . The only
and subsequently evaporates the bioink deposited on the limitation of SLA is that transparent liquid must be used
glass, which is then sprayed onto the substrate as liquid to allow light to pass through the material and achieve
drops [15,16] . Koch et al. employed laser-assisted printing to uniform crosslinking. Hence, the maximum cell density in
print skin fibroblast cells and human mesenchymal stem the bioink is restricted to approximately 10 cells/mL [27,28] .
8
cells (hMSCs) and reported a cell survival rate of ~98% and Unlike SLA, a DLP bioprinter immediately solidifies a
~90%, respectively . The main advantage of the system complete layer, instead of point-by-point photocuring. A
[17]
is that picogram-level printing resolution can be achieved typical bottom-to-top DLP bioprinter prints the bottom
using a nanosecond laser with an ultraviolet (UV) energy layer first and successively each new layer over the
wavelength. Furthermore, the equipment does not have previous one. The printing process uses a dynamic mask
a nozzle, and thus performs noncontact printing. The carrying a design pattern to transmit the light pattern to
disadvantage of laser-assisted bioprinting is the slow the substrate and a layering software to slice the 3D digital
gelation mechanism, which limits its high-throughput model to a certain thickness. Liquid crystal display, digital
printing [18,19] . micromirror device, and spatial light modulator have been

In electrohydrodynamic jetting (EHDJ), the metallic employed as dynamic masks in DLP printing . DLP offers
[29]
nozzle is loaded with bioink to form a spherical meniscus at a remarkable advantage over DBB and EBB technologies
the nozzle tip. An electric field is created on the meniscus by in terms of printing speed, wherein there is no increase in
generating a high voltage between the nozzle and substrate. printing time despite a more complex structure. Besides,
The accumulated mobile ions at the meniscus deform into DLP can fabricate a smoother 3D structure with improved
the Taylor cone due to electrostatic repulsions, and the structural integrity and mechanical strength, unlike the
droplets are ejected under an optimized voltage . The artificial interface formed between the droplets or fibers in
[20]
bioink adopts different modalities, such as Taylor jetting, DBB or EBB, respectively .
[20]
intermittent jetting, micro-dripping, unsteady status,
and breakdown, depending on the voltage . In EHDJ 1.1.3. Extrusion-based bioprinting
[21]
bioprinting, the size of droplets and the concentration In EBB, bioink containing cells is printed into a 3D
of cells affect the viability of cells. In addition, material construct through layer-by-layer formation with the aid of
propagation significantly reduces when the droplet size is fluid distribution and automated machine systems. Under
above 400 μm . The advantage of EHDJ is that the process the control of a computer, bioink is passed through a micro-
[22]
prevents excessive pressure, which may be destructive nozzle using piston, screw, or pneumatic approaches as a
to the cells. This method is selected for printing bioink continuous filament [30,31] . Screw-driven printers produce a
through a small orifice with large cell concentration and a more stable 3D-printed tissue structure from high-viscosity
high weight-to-volume ratio . bioink, whereas pneumatic-type printers inject hydrogels
[20]
with shear-thinning behavior, maintaining the filament
1.1.2. Photocuring-based bioprinting state of hydrogels even after extrusion . Recently, EBB
[32]
PBB is an approach of bioprinting that engages the bioprinters have been designed to simultaneously deposit
photopolymerization property of photosensitive polymers different bioinks with less cross-contamination using
under precisely controlled light without the issues of nozzle multiple printer heads [33,34] . The main advantage of EBB is
plugging and shear stress to the cells. This approach can the use of various types of printable bioinks, consisting of
be divided into stereolithography (SLA) and digital light cell clumps, microcarriers, acellular matrix components,
processing (DLP), depending on different light scanning and high-viscosity hydrogels. The printing speed and
modes. mechanical strength of the structure printed by EBB are
better compared to those printed by DBB . Although EBB
[35]
Charles W. Hull invented the SLA printing technology is a versatile method for fabricating prosthetic implants for
in 1984. An SLA bioprinter contains a tank filled with bioink TE, it has a low resolution exceeding 100 µm .
[36]
and a platform that moves up and down while printing.
The platform moves to the bioink surface and solidifies the 1.2. Printed gel properties
liquid upon exposure to UV light. The precision of SLA Among the different biomaterial forms, hydrogels are
is determined by various factors, including the scanning often used as printable bioinks in 3D printing because
speed, laser power, wavelength, and exposure time [23,24] . they can hold live cells, yield good resolution, and are
Through this method, porous structured tissue scaffolds chemically modifiable and mechanically adjustable with
can be printed in high resolution of approximately 1 µm in biodegradation properties [37,38] . Thus far, many polymeric
the desired geometric shape. Rapid bioprinting and higher biomaterials (natural and synthetic) have been used as a

Volume 9 Issue 1 (2023) 183 https://doi.org/10.18063/ijb.v9i1.635