Page 379 - IJB-10-5

International Journal of Bioprinting Tunable anisotropic gyroid bioscaffolds

its potential as a post-processing technique for 3D-printed The Young’s modulus of the specimens prepared
green parts to produce denser and more structurally robust through the SMWH process shows a similar trend with
ceramic materials. compressive strength with longer dwell times, which
were also notably higher compared to the specimens
Figure 4d and e presents the 3D reconstructed image
obtained through µ-CT showing the defect distribution prepared through the conventional furnace heating. At a
dwell time of 10 min, the MW10m exhibited a modulus
in the CS120m and MW120m specimens, respectively. of 1.94 ± 0.02 GPa, which gradually increased to 2.79 ±
Abundant cracks were formed, and larger defect volumes 0.17 GPa for MW180. In contrast, the modulus values of
were observed in the CS120m specimens after sintering the specimens prepared through the conventional heating
compared to MW120m. Under conventional heating, process were over 50% lower at each dwell time, ranging
the fast heating rate leads to uneven heating, creating from 0.87 ± 0.07 to 1.07 ± 0.14 GPa. The significant
thermal stress, and thus promote crack formation during improvement in mechanical properties observed in
the heating process. Cracks were also observed for the ceramic cube specimens is primarily attributed to
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the MW120m specimens, despite their smaller defect the accelerated densification process facilitated by the
volume. This can be attributed to the rapid generation SMWH process. In addition, the increased formation of
of gas from the decomposition of the binder during the cristobalite phase further contributes to the enhancement
debinding stage, leading to the formation of larger voids of mechanical strength. The specimens prepared through
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within the specimens and making them prone to crack conventional heating exhibit lower relative density, and
formation. Besides, the cracks were found on the lamellar therefore lower mechanical strength was recorded. The
facets. Owing to the layer-by-layer formation mechanism SMWH process offers several advantages including rapid
inherent to the DLP technology, weak points were created and more homogenous heating. This is achieved through
that are susceptible to crack initiation and propagation. a unique two-way heating mechanism that combines the
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Despite the advantages offered by the SMWH process, conventional mode of heating transfer from the MW
the formation of cracks may have a detrimental effect susceptor with the direct interaction between the MW field
on the mechanical properties of the sintered specimens. and the target materials. While prolonged sintering time
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Therefore, it becomes imperative to develop an appropriate can improve the mechanical properties of the specimens, it
heating process utilizing the MW technology in order to was found when the dwell time further increased from 120
minimize defects. to 180 min, the improvement in the mechanical properties
3.1.2. Effect of processing conditions on is limited. Consequently, a 120-min dwell time for the
mechanical properties sintering stage of the ceramic specimens was chosen for
The effect of dwell time on the mechanical properties the remaining of the study.
of the sintered ceramic cube specimens was evaluated. 3.2. Susceptor-assisted hybrid
The stress–strain relations of the specimens under pyrolysis-sintering process
uniaxial compression are presented in Figure 5a, while To address defects caused by debinding and sintering and
the compressive strength and the Young’s modulus improve the quality of the sintered ceramic specimens, we
of the specimens are summarized in Figure 5b and c, developed an innovative SHPS process. Figure 6a illustrates
respectively. The mechanical properties of the sintered the SHPS process for the DLP-printed specimens. During
specimens showed an increasing trend with longer dwell the first heating stage, instead of directly removing the
times. Specimens fabricated through the SMWH process binder in the 3D-printed structures in conventional
exhibited better mechanical properties compared to those process, a pyrolysis step at 600°C under N atmosphere
2
prepared through conventional furnace heating. At a dwell was introduced. Based on the TGA analysis, the majority
time of 10 min, the compressive strength of MW10m was of heteroatoms, including oxygen and hydrogen, were
measured to be 34.92 ± 3.49 MPa, which is 80% higher eliminated at this temperature. Consequently, the organic
than that of the CS180m. The compressive strength constituents underwent a transformation into pyrolytic
sharply increased to 86.62 ± 8.2 MPa for MW120m. As carbon, resulting in substantial structural shrinkage.
the dwell time was further increased, the enhancement in After pyrolysis, the SiO particles were brought closely
2
compressive strength became less pronounced, reaching a together before the complete removal of the residual
peak of 101.35 ± 19.62 MPa for the MW180m specimens. In pyrolytic carbon. This particle motion can improve the
comparison, the specimens prepared using a conventional densification during sintering. After the pyrolysis step,
furnace exhibited much lower compressive strength values the specimens were then subjected to a sintering step
at each dwell time, indicating significant enhancement of under air atmosphere. An intermediate heating step was
mechanical properties through the SMWH process. introduced at 800°C for complete removal of the pyrolytic

Volume 10 Issue 5 (2024) 371 doi: 10.36922/ijb.3609