Page 422 - IJB-9-2

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

weak resistance to deformation under load. Conversely, largest and the amplitude is the smallest, so the fluctuation
the elastic modulus of primitive is the lowest among the range is narrow, which means the flow of fluid in the
four TPMS scaffolds, and their elastic modulus are 18.67, Gyroid is stable and gentle. In addition, the flow velocity is
22.76, 23.38, and 13.97 MPa, respectively. generally kept at a high level even at the outlet. In contrast,
In addition, the cells in the scaffold need to go through the fluid velocity in diamond, I-WP, and primitive
the process of adhesion, extension, proliferation, and scaffolds fluctuates greatly and changes rapidly. From the
pressure curves (Figure 3F), it can be seen that the pressure
migration, and these processes require sufficient site and generally shows a downward trend with the increase of
space. Therefore, the specific surface area (ratio of surface flow depth. In the Diamond scaffold, the fluid pressure
area to volume) of the scaffold is important for cell growth.
Among the four TPMS scaffolds, the specific surface area drops particularly rapidly. As mentioned earlier, there is no
of diamond is the largest, which is 2.97 mm (Figure 3C), channel penetrating through the Diamond scaffold, so the
-1
while the primitive is the smallest, which is 1.73 mm , even fluid transport efficiency is low, causing fluid accumulation
-1
so, this value is 5.8 times that of the cubic scaffold of the at the inlet, increasing the fluid pressure at the inlet,
same size. Therefore, TPMS scaffold has more advantages resulting in a large pressure difference between the inlet
and outlet, which is about 7 Pa. The fluid pressure changes
than traditional cubic scaffold in providing cell growth in the other three types of scaffolds tend to approach and
space.
are relatively gentle. Their pressure drops between the inlet
The permeability of the scaffold determines the and the outlet are 3.69Pa (Gyroid), 3.25Pa (I-WP) and
transportation of nutrients and oxygen and the excretion 2.56Pa (Primitive), respectively. The permeability of TPMS
of waste in the scaffold. Good permeability allows the scaffolds (Figure 3G) shows that diamond scaffold has the
normal activities of cells in the scaffold, which is the lowest permeability of 2.82 × 10 m which is much higher
−9
2
basis of breast repair and reconstruction. In this study, we than that of breast tissue (5.44 × 10 m ) , indicating
2 [47,48]
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successfully established the permeability model of TPMS the strong permeability of TPSM scaffold loaded with
scaffold loaded with hydrogel for the understanding of hydrogel.
the flow behavior and the evaluation of the permeability According to the analysis of the above, it can be
of the breast scaffold. According to the results of the fluid seen that the fluid flow in diamond and I-WP scaffold
flow velocity nephogram (Figure 3D) in the scaffold, the is unstable with large fluctuation, while the primitive
different fluid flow patterns were exhibited in four TPMS scaffold shows poor resistance to deformation. In general,
scaffolds due to diverse internal structures. For instance, the Gyroid scaffold is more appropriate for breast
in Gyroid, I-WP, and Primitive scaffolds, channels reconstruction due to its acceptable mechanical properties
penetrated through the scaffold, facilitating fluid flow in and permeability. However, the designed Gyroid scaffold
these channels, which is conducive to the transportation exhibits a much higher elastic modulus compared to breast
of materials. However, in I-WP and primitive scaffolds, tissue (0.002 – 1 MPa), which may lead to inefficient cell
there are fewer channels penetrating through compared growth and breast tissue formation. Therefore, the Gyroid
with Gyroid, and these channels are vertically connected structure was further optimized in this research.
to other channels, resulting in the low fluid transportation
efficiency between channels. As for Gyroid, the penetrated 3.2. The optimization of TPMS scaffold
channels are evenly distributed and the connection between The relative density of TPMS scaffold directly influences
channels is smooth, which contribute to the fluid transport its elastic modulus. Thus, four types of Gyroid scaffolds
efficiency between channels; therefore, the fluid velocity (Figure 4A) with a relative density of 15%, 25%, 35%, and
distribution in the scaffold is relatively more uniform. 45% were designed and named Gyr-15, Gyr-25, Gyr-35,
While in diamond scaffold, there is no penetrated channels and Gyr-45, respectively. The mechanical properties of
and all channels are vertically connected with each other, these scaffolds were evaluated by the compression model
which leads to low efficiency of fluid transportation in the and then their elastic modulus was predicted (Figure 4B). It
scaffold. is obvious that the elastic modulus of the scaffold decreases
To further evaluate the flow of fluid in the scaffold, with the decrease of its relative density, and on the
the curve of fluid velocity varying with the depth of contrary, the average stress value increases continuously.
the flow was obtained through the simulation model Although the relative density of the scaffold decreased
(Figure 3E). The results show that the fluid velocity to 15%, its elastic modulus still shows a high value of
changes periodically in the TPMS scaffold, which is due to 6.56 MPa. However, the relative density of Gyroid is not
the periodic arrangement of the TPMS unit. Among four recommended to be below 15% because of the difficulty
TPMS scaffolds, the flow velocity period in Gyroid is the in fabrication and its fragile and unstable properties.

Volume 9 Issue 2 (2023) 414 https://doi.org/10.18063/ijb.685