Page 424 - IJB-9-2

International Journal of Bioprinting Design and 3D printing of TPMS breast scaffolds

235% of that at 2.6 mm. Excessive stress may lead to weak area of the Gyroid structure becomes small and narrow,
bearing capacity and instability of the scaffold. Therefore, and structural deformation and material loss occurred
with respect to elastic modulus and stress level, Gyr-2.6 was when the high-temperature nozzle contacts these areas
considered to be the best choice for breast reconstruction. during the printing process, causing the scaffold structure
Subsequently, this study also evaluated the permeability to be damaged and accompanied by the generation of fine
of Gyroid scaffolds with channels by the permeability filaments between channels, which leads to the blockage
model established before. The fluid velocity nephogram of channels. Therefore, from the manufacturing point
(taking Gyr-2.0 as an example) (Figure 4E) displays a more of view, it can be considered that the channel diameter
uniform fluid flow due to the integration of penetrated in Gyroid should not exceed 2.6 mm, otherwise, it will
channels, which further enhanced the connectivity between become more difficult to fabricate the scaffold through
channels, improving the fluid transport efficiency in the FDM. The porosity test results (Figure 5B) of the scaffolds
scaffold. The fluid velocity curves (Figure 4F) indicate that showed that the porosities of the printed scaffolds are close
the fluid velocity also shows the feature of periodicity in the to that of the designed models with deviations around 5%,
optimized Gyroid scaffold similar to the scaffold without owing mainly to the structural deformation and materials
optimization (named Gyr). However, the fluctuation loss occurred in the printing process. The actual channel
amplitude of the flow velocity is significantly decreased by diameters (Figure 5B) in the printed scaffolds are similar
adding channels. Specifically, the flow velocity fluctuation to that of the designed models, but due to the above
is 0.17 mm/s in the Gyr, while the flow velocity fluctuation printing defects, the diameter difference between channels
is 0.063 mm/s in the Gyr-2.0 and its flow stability is in a single scaffold is large, which may affect the expected
2.7 times that of Gyr. Moreover, with the increase of the mechanical performance of the scaffold.
channel diameter, the flow velocity fluctuation decreases In this study, the mechanical properties of the printed
gradually, especially when the diameter increases to TPMS scaffolds were evaluated by uniaxial single and cyclic
2.6 – 3.0 mm, the fluid flow tends to be gentler and more compression tests. The stress-strain curves (Figure 6A) of
stable. The fluid pressure curves (Figure 4G) prove that the TPMS scaffold were obtained through a uniaxial single
addition of channels in Gyroid scaffold did not change the compression test, from which three deformation stages of
fluid pressure trend. A significant change was observed in the scaffold can be observed. In the first stage, the stress
the initial fluid pressure where the pressure is decreased increases linearly with the strain, and the scaffold shows
from 3.70 Pa to a range of 0.60–1.12 Pa because of the elasticity. Therefore, this stage is called the elastic stage,
addition of channels, which indicates that the efficiency of which is the most important stage for the scaffold to resist
fluid transportation near the inlet is improved obviously. deformation. The elastic stage occupies 0 – 15% strain of
The permeability results (Figure 4H) also proved this scaffold during compression, and elastic modulus is the
speculation. The permeability of Gyroid scaffold with slope of the stress-strain curve at this stage. The results
added channels is much higher than that of Gyr, and the (Figure 6B) indicate that the elastic modulus of the scaffold
permeability increases with an increase of the channel decreases with the increasing of channel diameter. The
diameter generally. elastic moduli of Gyr-2.6, Gyr-2.8, and Gyr-3.0 are 0.83MPa,
0.33MPa, and 0.2MPa, which are consistent with the model
3.3. Fabrication and characterization of TPMS results and matched with natural breast tissue (0.002 – 1
scaffold MPa) [25-28] . When the strain increases to 15% the scaffold

The optimized TPMS scaffolds were successfully begins to yield, where the stress is maintained at a certain
manufactured through FDM (Figure 5A). Although there level with the increase of strain and the stress level decreases
are many pores in the structure, the Gyroid scaffold does with the increase of scaffold channel diameter. In this yield
not need to be supported during the printing process due process, the scaffold is constantly deformed under stress,
to its excellent printing self-supporting property which is contributing to the absorption of compression energy;
benefited from the continuity of the structure, omitting the therefore, this stage is called energy absorption stage. The
post-processing time and cost. The structural integrity and ability of the scaffold to absorb load energy depends on
features fidelity of Gyr-2.0, Gyr-2.2, Gyr-2.4, and Gyr-2.6 the level of stress and strain during this stage. The stress
were good and their channels were clearly visible. However, level decreases with the increase of channel diameter, while
when the channel diameter increased to 2.8 mm and 3.0 mm, the strain at this stage is approximately equal in every
the structural integrity of the local area of the scaffolds was scaffold, thus the energy absorption of scaffold is inversely
broken, and the filaments between the channels increase correlated to channel diameter. The energy absorption
significantly, causing partial channel blockage. The reason stage lasts until 50% strain is reached, accounting for
is that with the increase of the channel diameter, the local 35% of the strain window, indicating that TPMS scaffold

Volume 9 Issue 2 (2023) 416 https://doi.org/10.18063/ijb.685