Page 94 - IJB-9-1

International Journal of Bioprinting Progress in bioprinting of bone

printable ECM-based bioink containing 2% octapeptide gene expression of VEGFA and HIF1A. In athymic mice,
FEFEFKFK with AMP particles (ECM/AMP bioink) were short-term hypoxia (7-day hypoxia and 14-day normoxia)
developed [126] . Dental pulp stem cells were added to ECM/ promoted microvessel formation in vivo at 4 weeks and
AMP bioink and maintained 90% viability after 5 days in integration with the host vascular network but did not
bioprinted constructs. In comparison with the AMP-free affect osteogenic differentiation of SVFCs, representing
control group, ECM/AMP constructs showed greater the beneficial effects of short-term hypoxia in bone
mineralization and increased RUNX2, OPN, and COL1A1 regeneration.
mRNA expression at 21 days without the presence of With coaxial EBB, Raja et al. created 3D scaffolds
[92]
growth factors. Eight weeks after implanting ECM/AMP that used CDHA (core) and MC3T3-E1 cell-laden
constructs in rat cranial defects, a remarkable increase alginate (shell), thereby avoiding conventional sintering
in bone density as well as new bone formation were of ceramics after simultaneous printing of CDHA and
observed in the defect. Using a microparticulate bioink the cell-laden hydrogel. Compared to alginate-only
composed of poly(lactic-co-glycolic acid) (PLGA), PEG, scaffolds (0.3 MPa), core/shell scaffolds have a higher
and carboxymethyl cellulose, Sawkins et al. [127] achieved compressive modulus (7 MPa), and CDHA-only scaffolds
a bioprinted construct with mechanical properties disintegrated after compression, showing that core/shell
comparable to those of human cancellous bone (Young’s scaffolds balance the poor mechanical properties of
modulus: 57.3 MPa) and the pore sizes of 65 – 77 μm. hydrogel with the brittleness of ceramic. Kim et al.
[84]
Furthermore, the bioprinted constructs released lysozyme fabricated an α-TCP/collagen cell-laden scaffold with
for 15 days, and a high level of protein activity was observed MC3T3-E1 cells, where a layer of porous α-TCP/collagen
for 9 days.
fibers without cells was extruded for mechanical stability,
3.1.6. Hybrid constructs with mechanical followed by deposition of collagen bioinks onto the
reinforcement porous layer, and this process was repeated until a 3D
scaffold was obtained. On the bioprinted scaffolds, more
As mentioned in section 2.6., to obtain a clinically viable cells and a more homogenous distribution of cells
relevant mechanical strength, hybrid constructs are usually were found compared with the controls, namely, the cell-
fabricated by EBB, such as using a dual-nozzle setup to laden collagen-only scaffold and α-TCP/collagen scaffold
print mechanical supporting frames along with cell-laden with dipping-loaded cells. Ahlfeld et al. [128] prepared
bioinks and coaxial nozzle to print core-shell filaments biphasic scaffolds by alternately extruding two materials,
(Figure 2A). Lee et al. demonstrated a hybrid scaffold namely, the cell-laden alginate-methylcellulose blend
[44]
containing PCL and cell-embedded alginate fibers, where (ALG/MC) and calcium phosphate cement (CPC). The
the alginate fibers provided biological functionality to the compression modulus of the biphasic scaffold containing
construct, while the PCL fibers regulated the mechanical 50% CPC and ALG/MC was much higher than that of
properties. Such a design resulted in a notable increase in the monophasic scaffolds of ALG/MC (31 ± 9 MPa vs.
Young’s modulus and ultimate tensile strength compared to 37 ± 5 kPa). Osteochondral scaffolds were generated with
alginate-only scaffolds. Furthermore, an integrated tissue- calcified cartilage between CPC and ALG/MC zones,
organ printer able to handle several biomaterials (including which resembled articular cartilage and subchondral
gelatin, fibrinogen, HA, and PCL) was established by Kang bone, respectively.
et al. to construct human-scale and mechanically-stable
[91]
tissues. In the process of reconstructing the mandible Zhai et al. [129] developed a biodegradable material
bone, authors bioprinted an amniotic fluid-derived stem (bioink A) composed of poly(ethylene glycol) diacrylate
cell-laden hydrogel, a mixture of PCL and TCP, as well as (PEGDA) and laponite nanoclay (PEG-Clay). A structure
Pluronic F127. Furthermore, rat calvarial bone constructs was created using a two-channel 3D bioprinting method
were generated in a circular shape using human amniotic together with another composite (bioink B) composed
fluid-derived stem cells (hAFSCs), revealing restored of rat osteoblasts (ROBs) loaded within HA. Bioink A
vascularized bone without necrosis at all implant regions, improved the mechanical properties and cell adhesion, and
while the control group treated with scaffold only had the release of magnesium and silicon bioactive ions was
negligible bone tissue formation. Kuss et al. adopted conducive to the osteogenic differentiation of cells. The
[27]
SVFCs, which maintained the characteristics of ECs, bioink B ensured the uniform distribution of cells in the
in creating bone constructs with PCL/HAp and SVFC- scaffold and a high survival rate (e.g., >95% after 1 day).
laden MeHA/GelMA bioinks. In a short-term (<21 days) In vitro experiments showed that the ALP activity of ROBs
hypoxic culture in vitro, osteogenic differentiation of within the PEG4K-Clay scaffolds was remarkable. In vivo
SVFCs was not affected, which, in turn, promoted vascular tibia repair showed that the regenerated bone size using

Volume 9 Issue 1 (2023) 86 https://doi.org/10.18063/ijb.v9i1.628