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International Journal of Bioprinting Hydrogels for 3D bioprinting

hydrogel solution and its high shear thinning. In 2015, used a combination of 3D-printed GO with SA and gelatin
Hong et al. demonstrated that adding nanoclay to a SA- as the basis for a novel bioink to support human adipose-
[53]
PEG-blended hydrogel solution can adjust its viscosity derived stem cells (ADSCs). After investigating the effects
and improve rheological properties for the first time. They of different GO concentrations on cell affinity and viability,
soaked the printed SA-PEG-nanoclay grid scaffold in a they found that GO concentrations in the range of 0.05%
collagen solution containing human embryonic kidney to 0.5% (w/w) were widely distributed in the SA/gelatin
cells (HEK). Then, the collagen solution formed gels in the scaffold and could promote the growth and differentiation
pores of the scaffold, and the cells maintained high viability of human ADSCs. Cheng et al. [115] loaded GO nanoparticles
during the 7-day culture process. The nanocomposite (GO-np) into the hydrogel to protect cartilage tissue through
hydrogel is tougher than natural cartilage and has the the Rank/Rankl/OPG signaling pathway (Figure 6B). At a
ability to encapsulate cells. It can be used to print some wavenumber of 2400 cm , it proved that C≡C in GO-np is
-1
bionic tissues, such as human ears and noses (Figure 5B). involved in the adsorption process. CCK8 test shows that
Overall, compared with the polymer-based hydrogels GO-np nanocomposite hydrogel is beneficial to improve
mentioned above, inorganic nanocomposite hydrogels as cell viability (Figure 5C(i) and (ii)). The results showed
3D bioprinting inks can facilitate repair not only by forming that GO-np may be used as a carrier for drug delivery to
solid chemical bonds with adjacent tissue surfaces through control its release to achieve the purpose of protecting
the elements released during their degradation, but also cartilage tissue. GO has certain advantages as a drug carrier,
by forming gels with other materials through electrostatic and it can be widely used in the field of biomedicine as an
interactions to anchor cells in 3D structures, thus enabling intelligent nanomaterial in future.
high-fidelity printing [21,103] . However, their more complex GO can not only induce cartilage differentiation, but
preparation process and potential immunogenicity are one also has obvious osteogenic differentiation effects on bone
of the main reasons why they are currently not widely used regeneration. The composite material of GO combined
in clinical repair. with SA hydrogel shows a good performance. The bioinks
mixed with 3% SA and 0.5 mg/mL GO combined with
4.2. Carbon-based nanocomposite hydrogels MSCs were printed into a 3D scaffold. MSCs showed
4.2.1. Graphene and its derivatives good proliferation and high survival rate in an oxidative
As the basic structure of graphitized materials, graphene stress environment. The addition of GO overcomes the
is considered one of the most powerful materials so far. disadvantages of low printing quality and poor structural
Graphene oxide (GO) and reduced graphene oxide (rGO) stability of SA hydrogel to a certain extent, which could
are common derivatives. Because graphene has unique enhance the mechanical properties of the hydrogel
physicochemical, biological, and electronic properties, the scaffold, promote cell proliferation, and induce osteogenic
applications of graphene and its derivatives in the field of differentiation [116] . It can be seen that the nanocomposite
biomedicine are mainly in tissue engineering, biosensors, of GO and hydrogel polymer has the potential to
drug delivery, gene therapy, bioimaging, etc. [107,108] In recent become a candidate material in bone tissue and cartilage
years, 2D graphene has been introduced into the hydrogels tissue engineering. Besides, in the field of neural tissue
to form composite materials, which were used as a bioink to engineering, graphene and GO are suitable for printing
obtain a 3D structure through 3D bioprinting technology. neural tissue structures containing stem cells. It has been
This is an innovative and revolutionary technological proven that an extremely lower content of graphene or
change, which has broad application prospects in GO (25 ppm) mixed with biodegradable PU hydrogel
tissue engineering [109,110] . can be used for the bioprinting of neural stem cells. To

GO can be obtained by oxidative exfoliation of graphite, reduce the toxic effects of graphene on cells, a layer of
which is several nanometers to several micrometers in Pluronic was coated on the surface. This research proposes
size. It has a variety of chemical functional groups such a successful solution to the major cytotoxicity problem of
as carboxyl groups, hydroxyl groups, and epoxy groups, graphene-based materials. The rheological properties of
which can combine with various molecules to show strong this graphene-based composite nanomaterial provide a
interaction. Therefore, GO can stably exist in an aqueous suitable living environment for cell survival, increase cell
solution [111,112] . The nanocomposite formed by GO and the oxygen metabolism, and have a significant neurological
hydrogel exhibits enhanced mechanical properties. Besides, differentiation phenomenon [117] .
it interacts with the polymer with hydrogen donor/acceptor
functional groups in the hydrogel to act as a physical 4.2.2. Carbon nanotubes
crosslinker through hydrogen bonding. Therefore, the Like graphene and its derivatives, carbon nanotubes
hydrogel can form a stable network structure [113] . Li et al. [114] (CNTs) also have excellent electrical conductivity, optical

Volume 9 Issue 5 (2023) 221 https://doi.org/10.18063/ijb.759