133
polytetrahydrofuran- diacrylate (PTHF-DA) groups with different end groups—with
two laser printing technologies, stereolithography processing (SL) and multiphoton
polymerization (MMP). The polymeric coil structure of the PTHF-DA was thought
to contribute to the physical properties of the printed construct (including melting
and crystallization points) as well as to the branched shape of the final construct.
The team further tested the structure for the shape memory effect (SME). The fabricated polymer, which was reshaped by several winding springs, showed an excellent SME by returning to its original shape. This property has important implications
in the application of printed vascular tissue to clinical settings.
Laser bioprinted large-scale vessels were also investigated in vivo. Melchiorri
et al. implanted laser-printed vascular grafts in mice [35]. The group used biodegradable poly(propylene fumarate) (PPF) to fabricate vasculature with DLP technology. The mechanical properties of the printed grafts were evaluated prior to the
implantation surgery. At the 6-month follow-up period, the patency of the graft
in vivo was 100%, and the degradation of the graft mass was noted. However, maintaining structural and mechanical support for the tissue construct has yet been met
due to the demand of adequate neotissue formation. Vascular remodeling in the
interface between the grafted and native vessels was observed, and neovessel formation was mainly noted on the inner surface of the lumens. This experiment provided
an insight into the application of laser-printed vascular constructs and the potential
for vascular remodeling in vivo.
5.2.4 Scaffold-Free 3D Printing
5.2.4.1 Principle
Scaffolds have traditionally been used as supportive infrastructures for 3D printed tissues. Though scaffold-based 3D printing modalities have been successfully used to
print native-like tissue constructs, the scaffolds themselves pose concerns. These
include biocompatibility, immunogenicity, degradation rate, cytotoxicity of the degradation products, and altered properties of printed tissues due to residual polymers [6].
Neotissue formation requires the microenvironment to provide sufficient physical support and nutritional supply to allow for continuous cell growth and uninterrupted cellcell signal transduction, all of which are impacted by the presence of scaffolding. Given
the limitations of scaffold-based printing technologies, scaffold- free 3D printing techniques have been developed. These methods use cell-only bioink to increase the concentration of printed cells. Inkjet (or droplet-based) and extrusion-based 3D printing
approaches have all been used with cell-only bioink to fabricate scaffold-free constructs. Cell-free bioink can be formulated in two ways—as either a cell pellet or as cell
aggregates. In scaffold-free bioprinting, the cellular bioink is printed in a supporting
cast, in which the maturation of the tissue structure takes place [7, 42].
5 3D Printing Technology for Vascularization
polytetrahydrofuran- diacrylate (PTHF-DA) groups with different end groups—with
two laser printing technologies, stereolithography processing (SL) and multiphoton
polymerization (MMP). The polymeric coil structure of the PTHF-DA was thought
to contribute to the physical properties of the printed construct (including melting
and crystallization points) as well as to the branched shape of the final construct.
The team further tested the structure for the shape memory effect (SME). The fabricated polymer, which was reshaped by several winding springs, showed an excellent SME by returning to its original shape. This property has important implications
in the application of printed vascular tissue to clinical settings.
Laser bioprinted large-scale vessels were also investigated in vivo. Melchiorri
et al. implanted laser-printed vascular grafts in mice [35]. The group used biodegradable poly(propylene fumarate) (PPF) to fabricate vasculature with DLP technology. The mechanical properties of the printed grafts were evaluated prior to the
implantation surgery. At the 6-month follow-up period, the patency of the graft
in vivo was 100%, and the degradation of the graft mass was noted. However, maintaining structural and mechanical support for the tissue construct has yet been met
due to the demand of adequate neotissue formation. Vascular remodeling in the
interface between the grafted and native vessels was observed, and neovessel formation was mainly noted on the inner surface of the lumens. This experiment provided
an insight into the application of laser-printed vascular constructs and the potential
for vascular remodeling in vivo.
5.2.4 Scaffold-Free 3D Printing
5.2.4.1 Principle
Scaffolds have traditionally been used as supportive infrastructures for 3D printed tissues. Though scaffold-based 3D printing modalities have been successfully used to
print native-like tissue constructs, the scaffolds themselves pose concerns. These
include biocompatibility, immunogenicity, degradation rate, cytotoxicity of the degradation products, and altered properties of printed tissues due to residual polymers [6].
Neotissue formation requires the microenvironment to provide sufficient physical support and nutritional supply to allow for continuous cell growth and uninterrupted cellcell signal transduction, all of which are impacted by the presence of scaffolding. Given
the limitations of scaffold-based printing technologies, scaffold- free 3D printing techniques have been developed. These methods use cell-only bioink to increase the concentration of printed cells. Inkjet (or droplet-based) and extrusion-based 3D printing
approaches have all been used with cell-only bioink to fabricate scaffold-free constructs. Cell-free bioink can be formulated in two ways—as either a cell pellet or as cell
aggregates. In scaffold-free bioprinting, the cellular bioink is printed in a supporting
cast, in which the maturation of the tissue structure takes place [7, 42].
5 3D Printing Technology for Vascularization