Page 271 - IJB-9-3

International Journal of Bioprinting Performance of Bredigite-based bone scaffolds

Figure 6. Mechanical properties of two scaffolds at different porosities. Green represents the open-rod model support, and orange represents the TPMS
model support. (a) Ultimate tensile strength. (b) Strain when the support collapses and breaks.

and becomes progressively denser under pressure. As of the TPMS model with 70% porosity is approximately
the strain increases, the stress gradually increases until it 10 Mpa higher than that of the open-rod model with 50%
exceeds that of the first dense layer, causing the hole wall to porosity, indicating that the strength of the TPMS model
bend and collapse. The corresponding powder further fills can be improved by optimizing the single-cell structure
the holes in the second layer, and the process is repeated and arrangement of the scaffold, and the TPMS model
until the entire ceramic collapses. bracket has a higher strength than the commonly used
open-rod model. The strain values of the 50, 60, and 70%
3.1.2. Compressive strength open-rod models are 2.89 ± 0.39, 2.85 ± 0.41, and 2.79 ±
Figure 6a shows the ultimate compressive strengths of 0.53, respectively. All of them are smaller than the TPMS
the two supports, and Figure 6b shows the strain when model scaffolds, indicating that the TPMS structure has
collapse occurs. The ultimate compressive strengths of good ductility. Taken together, the mechanical strength of
the TPMS models with 50, 60, and 70% porosity were the TPMS model is higher than that of the open-rod model
65.45 ± 2.45 Mpa, 59.16 ± 5.15 Mpa, and 55.09 ± 3.9 Mpa, and satisfied the requirements for clinical use in repairing
respectively. With an increase in porosity, the ultimate bone defects.
compressive strength of the scaffold decreased significantly.
Generally, the compressive strength of cancellous bone 3.2. Analysis of mechanical properties of scaffolds
is 1–10 Mpa, and that of dense bone is 1–100 Mpa. during degradation
However, in the clinical treatment of bone defects, it is Figure 7 shows the compressive strength and its variation
not clear whether cancellous-like scaffolds will be filled at with the degradation time. With the extension of the
the site of cancellous bone, while the site of dense bone degradation time, the compressive strength of the bredigite
will be filled with scaffolds similar to dense bone. This scaffold gradually decreases; however, this overall trend
necessitates the bone tissue-engineered scaffolds with a gradually slows down. The TPMS scaffolds with 50%
high porosity to achieve the compressive strength, and porosity show the slowest decline in mechanical strength.
the TPMS model scaffolds with three different porosities After 8 weeks of degradation, its ultimate compressive
to meet this requirement. For TPMS models with 50, 60, strength is still 47.89 ± 3.67 Mpa, equivalent to a decrease
and 70% porosity, the strain during collapse and breakage of only 28%. With an increase in porosity, the compressive
is 5.4 ± 0.36, 5.62 ± 0.43, and 5.37 ± 0.41, respectively. The strength decreases rapidly. With the increase in porosity,
strain during collapse does not change significantly with the difference in the compressive strength between the
an increase in scaffold porosity, indicating that the ductility TPMS model scaffold and open-rod scaffold becomes
of bone tissue-engineered scaffolds made of the same increasingly obvious.
material is unrelated to porosity. However, it is related to
the structure of the support. The ultimate compressive 3.3. Analysis of pH change in degradation solution
strength of the open-rod models with 50, 60, and 70% during scaffold degradation
porosity is 43 ± 3.97 Mpa, 38 ± 1.85 Mpa, and 32 ± 5.32 Mpa, As shown in Figure 8, the initial sharp increase in pH over
respectively. Compared with TPMS scaffolds with the same time is due to the exchange of calcium silicate cations,
porosity, the ultimate compressive strength is reduced by especially Ca , with H or H O in the SBF. After 4 days of
2+
+
+
3
approximately 20 Mpa. The ultimate compressive strength degradation, the pH level reaches a relatively stable level,
Volume 9 Issue 3 (2023) 263 https://doi.org/10.18063/ijb.708