Page 441 - IJB-10-5

International Journal of Bioprinting Bioprinting for large-sized tissue delivery

presenting compressive stress–strain curves were included The lattice architectures were first 3D printed and
to compare with this study. GelMA is commonly used photocrosslinked (Figure S7A, Supporting Information)
as a control group in these studies, and we highlighted to assess the shape fidelity of GP hydrogel using equations
the optimal conditions for GelMA (Figure 2H; Table previously established by our group. The Pr was calculated
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S2, Supporting Information). Compared to previous to be 1.03 ± 0.02, suggesting good shape fidelity with a
studies, this is the first study to report on a GP mixture Pr value in the range of 0.9~1.1 (Figure S7B, Supporting
with superelasticity and fatigue resistance features. Information). Thereafter, architectures with different
The preparation and crosslinking procedure of GP was filling patterns, i.e., sinusoidal, Hilbert, and zigzag curves,
versatile and did not require a complicated dispersion were designed and smoothly printed (Figure 3D). The
or freezing process, providing a generalized strategy for decoupled strategy enables independent photocrosslinking
developing novel mechanically reinforced hydrogels for with the culture dish lid closed, maintaining sterility and
tissue delivery applications. reducing water evaporation from the hydrogel (Figure S8,
Supporting Information). The crosslinked architectures
3.2. 3D printing, stability, and deformation behavior were then immersed in the culture medium at 37°C for
of GP architectures 16 days to evaluate the material degradation under cell
3D printing technology is widely used to fabricate culture conditions. Semi-quantitative analysis displayed no
architectures with customized geometries. To fabricate significant differences in filament diameter after the 16-day
large-sized architectures with high injection capacity using culture (Figure 3E), suggesting good structural stability and
GP hydrogel, a decoupled strategy of micro-extrusion potential for long-term cell culture. Next, the deformation
and photocrosslinking was utilized instead of commonly behavior of circular ring-shaped printed architectures was
used DLP methods. The reversible thermal crosslinking assessed. The samples presented exemplary deformation
of GelMA was employed to regulate the gelation status capacity and fatigue resistance, enduring 30 pinch cycles
during cooling for smooth extrusion. Subsequently, the and five stretch cycles, as well as recovering with intact
primary printed architectures were photocrosslinked structure (Figure 3F; Video S2, Supporting Information).
by the white light source to establish a stable covalent This deformation behavior warranted further investigation
network. This strategy enables independent regulation into the injection capacity of large-sized printed
of bioprinting and photocrosslinking and is compatible architectures with more complex geometries.
with widely accessible bioplotting devices.
3.3. 3D printing of large-sized architectures with
The rheological characteristics of the hydrogel matrix high injection capacity
are vital for a stable extrusion process. Upon rheological Repetitive units with different geometries exhibit tunable
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analysis, 10G2.5P without photocrosslinking displayed Poisson’s ratios during deformation: honeycomb patterns
typical thermoresponsive characteristics and sol-gel display a positive Poisson’s ratio (PPR); semi-re-entrant
phase transition with a gelation point at 19°C (Figure 3A). honeycomb repetitive patterns mostly display zero Poisson’s
At a 20 min temperature preservation process at 19°C, ratio (ZPR); while re-entrant honeycombs, sinusoidal
10G2.5P maintained a constant gel phase and exhibited meshes, lozenge grids, and curved meshes demonstrate an
stable viscoelasticity with G’ of 306.6 Pa and G” of 9.7 auxetic effect, inducing a negative Poisson’s ratio (NPR).
Pa (Figure 3B), similar to that of gelatin/alginate bioink, In this study, the models mentioned above were designed
thereby facilitating high cell viability after bioprinting. (Figure 4A). The corresponding architectures were printed
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The viscosity curve suggests that GP expresses a typical with a dimension of 15 × 15 × 1 mm for parallel studies
shear-thinning behavior under shear force (Figure 3C). (Figure 4B). A systematic evaluation of injection capacity
These results indicate that GP is compatible with micro- was performed utilizing silicone tubes and dispensing
extrusion printing, displaying suitable thermoresponsive needles with inner diameters ranging from 1 to 5 mm,
and shear-shining properties. Using the multi-nozzle comparable to the sizes of medical catheters or syringe
bioprinter with a precise temperature-control module needles widely used for clinical applications (Table S4,
(Regenovo, China), the gelation conditions of the bioink Supporting Information). After injection through the
can be accurately controlled to facilitate continuous silicone tubes and needles, the injection capacity was
extrusion of smooth filaments (Figure 3C). Hence, the evaluated via the integrity of geometric features and the
temperature of the syringe holder was set at 2°C higher fracture of filaments. Additionally, the injection capacity
than the gelation point to enhance bioink flow and cell was semi-quantitatively calculated from the values of S inject
survival. The temperature of the nozzle holder was set (minimum sectional area of the needle used) and S architecture
at 2°C lower than the gelation point to facilitate rapid (maximum sectional area of the architecture; i.e., 15 × 15
gelation and filament formation. mm), using the equation listed below:

Volume 10 Issue 5 (2024) 433 doi: 10.36922/ijb.3898