Page 386 - IJB-10-5

International Journal of Bioprinting Tunable anisotropic gyroid bioscaffolds

proliferation efficiency, with a higher cell count observed sintering 3D-printed ceramic structures, such as crack
at day 7. Conversely, the γ.25-FGgy scaffold exhibited the formation, thus offering a promising solution to enhance
slowest cell proliferation rate. This decrease in proliferation the quality of 3D-printed ceramic scaffold. By integrating
rate correlates with the reduction in total surface area, advanced functional materials like piezoelectric ceramics,
which decreases from 1551.9 mm² for γ.50-FGgy to 1363.8 this processing method will accelerate the development of
mm² for γ.25-FGgy. Additionally, as the aspect ratio of 3D-printed ceramic structures for cutting-edge biodevices.
the unit cell of the gyroid structures increases with lower The comparative study between SMWH process and
γ values, the average Gaussian curvatures of the scaffolds conventional furnace heating revealed advantages of MW
are affected. This alteration in curvature can significantly technology in enhancing the physical and mechanical
impact the proliferation behavior of mesenchymal stem properties of the ceramic specimens. The compressive
cells, as supported by previous studies. To further strength of the MW120m was measured at 86.62 ± 8.2 MPa,
7,36
evaluate the cell seeding efficiency, the cell density on over 1.8 times higher than the compressive strength of
the scaffold over the 7-day culture period was calculated RCS120m. The SMWH process resulted in higher relative
by normalizing the cell number to the surface area densities and different crystalline structures compared to
(Figure 10d). As the γ value decreased (indicating a conventional furnace heating, which contributed to the
higher aspect ratio), the cell counts per square millimeter mechanical enhancement of the 3D-printed specimens.
of scaffold surface area decreased significantly, from 46 The SMWH process facilitates rapid and efficient energy
cells/mm² for γ.50-FGgy to 33 cells/mm² for γ.25-FGgy. transfer to 3D-printed ceramic specimens through a two-
This finding suggests that while anisotropic properties of way heating mechanism. 23,32 This rapid energy transfer of
the scaffold can be achieved by tuning the γ value, there MW heating decreases sintering activation energy and
is a trade-off in cell proliferation rates. In comparison, processing temperature, 19,20 promoting densification,
37
the 57.55VF-gy specimens, which lacked porosity which result in an improvement in relative density from
gradients, exhibited the highest cell density after 7 days 95.02% to 96.95%. Additionally, the intrinsic heating
of culture. This indicates that the presence of structural mechanism of MW technology reduces activation energy
gradients, while beneficial for mimicking natural bone for nucleation and enhances crystallization during the
anisotropy, may reduce the overall cell proliferation sintering process. Despite the significant enhancements
20
rate due to the decreased effective surface area and in the mechanical properties, severe crack formation was
altered curvature. Overall, these results indicate that observed, indicating the need for further improvement of
gyroid scaffolds with anisotropic properties offer notable the SMWH process.
benefits in mimicking natural bone structures and could
potentially mitigate in vivo stress shielding. In addition, An innovative SHPS process was established to reduce
designing them requires careful consideration to strike a the defects caused by debinding and sintering. From
balance between mechanical properties and optimal cell the morphological and physical characterizations, the
proliferation rates. process led to denser ceramic specimens after sintering
with minimized defects compared to both SMWH and
4. Discussion conventional furnace heating. SEM and µ-CT analyses
(Figure 6) confirmed the reduction in crack formation
This study introduces a mathematical design approach and defect volume in SHPS specimens. Compared with
for customizing 3D bioscaffolds. By setting appropriate RCS120m which had a defect volume of 4.64%, the defect
geometric parameters (α, β, and γ) and the iso-surface volume of SHPS120m was reduced by 16.80–3.86%.
function C (x, y, z) in the level-set equations, sheet gyroid Consequently, a significant improvement in mechanical
scaffolds with spatially controlled porosity and anisotropic properties for SHPS120m specimens was recorded, with
properties were generated. Given that other types of TPMS
share similar mathematical descriptions, this design about 335% increase in compressive strength (158.35 ±
approach does not limit to sheet gyroid structures but can 19.76 MPa) and a 28.2% in Young’s modulus (3.14 ± 0.04
also be applied to other TPMS variations. Moreover, we GPa), respectively.
established an innovative SHPS processing method, utilizing The reduction of defects is primarily attributed to
MW heating technology, to effectively debind and sinter the additional pyrolysis step during the SHPS process.
the 3D-printed ceramic green specimens. The comparison Unlike traditional debinding methods that involve
between SMWH process and conventional furnace heating removing the polymer, the polymer is transformed
highlights the advantages of MW technology in ceramic into carbon during pyrolysis. Pyrolysis transforms the
processing. Additionally, the SHPS process addresses polymer into carbon. This transformation potentially
the critical challenge associated with MW technology in reduces gas formation and release during the process,

Volume 10 Issue 5 (2024) 378 doi: 10.36922/ijb.3609