135
macrovascular tissue in a porcine abdominal aortic model [30]. The team optimized
their 3D printing algorithm to consider the precise geometries of the aorta. A tubular
construct was printed, in a self-support model with mouse embryonic fibroblasts
(MEFs), using this proposed algorithm.
More recently, Itoh et al. tested a scaffold-free 3D printed vascular graft in vivo,
using an aortic graft interposition surgery in a rat model [23]. In this study, the vascular graft was printed using HUVECs, human aortic smooth muscle cells
(HASMCs), and human normal dermal fibroblasts (HNDFBs). The graft underwent
remodeling in vivo, demonstrating enlargement of the lumen. The biocompatibility
of the graft was demonstrated by the significantly larger amount of extracellular
matrix that was secreted in the scaffold-free graft, when compared to a scaffoldbased graft.
5.3 Discussion
There are various 3D bioprinting modalities, each with particular strengths and
weaknesses, depending on the type of vascular construct that is desired. Inkjet printing is very cost-effective and provides medium to high resolution of printed constructs. However, the cell density of bioinks that can be successfully printed and the
capacity to construct complex, precise 3D structures are limited due to the dropletbased technology, despite controlled positioning of the print head improving the
precision of droplet deposition [22]. Furthermore, even with the development of
“droplet-on-demand technology”, the nozzle used in inkjet printing may have detrimental effects on cell survival due to the thermal and physical stress exerted on the
bioink [5, 16].
Extrusion-based printing is also cost-effective and provides the versatility of
using bioinks that consist of cells encapsulated in hydrogel prior to printing. This
technology produces constructs with good mechanical properties because it allows
for printing with high viscosity and high cell density materials. Another advantage
of extrusion printing is the ability to form solid 3D structures using filament form
deposition of the hydrogel. However, printed cell viability is lower than that of the
other modalities [37]. Also, the even spacing of cells within the hydrogel cannot be
guaranteed using this technique, which could compromise the cell-to-cell contact.
Additionally, the printing resolution of extrusion printing is limited, compared to
other 3D printing methods [13].
Laser-based 3D printing also allows for printing with high cell density bioink
and provides excellent resolution due to the nozzle-free approach. However, there
are disadvantages associated with this technique, including its high cost and long
printing times. Furthermore, the long-term cytotoxicity effects, from the irradiation
of the high-power laser, are yet to be determined [17].
The scaffold-free approach to 3D bioprinting also carries the advantage of being
able to print bioinks with high cell densities and for creating constructs that preserve
and promote cell-cell interactions. However, the structural integrity and mechanical
5 3D Printing Technology for Vascularization
macrovascular tissue in a porcine abdominal aortic model [30]. The team optimized
their 3D printing algorithm to consider the precise geometries of the aorta. A tubular
construct was printed, in a self-support model with mouse embryonic fibroblasts
(MEFs), using this proposed algorithm.
More recently, Itoh et al. tested a scaffold-free 3D printed vascular graft in vivo,
using an aortic graft interposition surgery in a rat model [23]. In this study, the vascular graft was printed using HUVECs, human aortic smooth muscle cells
(HASMCs), and human normal dermal fibroblasts (HNDFBs). The graft underwent
remodeling in vivo, demonstrating enlargement of the lumen. The biocompatibility
of the graft was demonstrated by the significantly larger amount of extracellular
matrix that was secreted in the scaffold-free graft, when compared to a scaffoldbased graft.
5.3 Discussion
There are various 3D bioprinting modalities, each with particular strengths and
weaknesses, depending on the type of vascular construct that is desired. Inkjet printing is very cost-effective and provides medium to high resolution of printed constructs. However, the cell density of bioinks that can be successfully printed and the
capacity to construct complex, precise 3D structures are limited due to the dropletbased technology, despite controlled positioning of the print head improving the
precision of droplet deposition [22]. Furthermore, even with the development of
“droplet-on-demand technology”, the nozzle used in inkjet printing may have detrimental effects on cell survival due to the thermal and physical stress exerted on the
bioink [5, 16].
Extrusion-based printing is also cost-effective and provides the versatility of
using bioinks that consist of cells encapsulated in hydrogel prior to printing. This
technology produces constructs with good mechanical properties because it allows
for printing with high viscosity and high cell density materials. Another advantage
of extrusion printing is the ability to form solid 3D structures using filament form
deposition of the hydrogel. However, printed cell viability is lower than that of the
other modalities [37]. Also, the even spacing of cells within the hydrogel cannot be
guaranteed using this technique, which could compromise the cell-to-cell contact.
Additionally, the printing resolution of extrusion printing is limited, compared to
other 3D printing methods [13].
Laser-based 3D printing also allows for printing with high cell density bioink
and provides excellent resolution due to the nozzle-free approach. However, there
are disadvantages associated with this technique, including its high cost and long
printing times. Furthermore, the long-term cytotoxicity effects, from the irradiation
of the high-power laser, are yet to be determined [17].
The scaffold-free approach to 3D bioprinting also carries the advantage of being
able to print bioinks with high cell densities and for creating constructs that preserve
and promote cell-cell interactions. However, the structural integrity and mechanical
5 3D Printing Technology for Vascularization