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3D-printed borate glass scaffolds for bone repair
A B

Figure 2. (A) Unit cells and pore shapes of cubic and spherical architecture scaffolds, (B) pore volume
variation of spherical and cubic scaffolds with porosity. Cylindrical extensions to the spherical pores
were designed to maintain sufficient pore size for powder removal from the scaffold.

Overall, the differences in scaffold compressive Table 3. Compressive modulus of scaffolds at
strength at higher porosities (>55%) were not designed porosities (in GPa).
as significant as they were at lower porosities Scaffold 50 60 70 80
(<35%). Architecture of scaffold contributes to Cubic 1.9±0.3 1.2±0.3 0.7±0.1 0.6±0.2
cell proliferation, tissue growth, and scaffold Spherical 1.8±0.2 1.1±0.4 0.8±0.1 -
structural integrity. Therefore, it is crucial to X 1.0±0.2 0.8±0.2 0.3±0.0 -
optimize the porosity and architecture of a Diamond 1.0±0.2 1.0±0.1 0.6±0.1 0.3±0.0
scaffold, depending on the application. Another Gyroid 1.4±0.3 1.1±0.2 0.8±0.2 0.4±0.1
important aspect of the scaffold structural integrity
is the elastic modulus during compression which σ σ = o e − BP (1)
measures the scaffold stiffness. Scaffolds with where,
higher stiffness are not desired in load-bearing σ - Strength of porous part; σ - Strength of dense
applications as they are known to cause stress part; o
shielding effect. However, as borate glass B - Empirical constant (pore shape factor);
scaffolds fabricated using the SLS process do p - Porosity fraction;
not possess enough structural strength for load-
bearing applications and are suitable for non-load Mechanical properties of porous ceramic parts
bearing applications and, the scaffold stiffness are dependent on porosity and pore shape. The
may not play a major role in bone regeneration. results reported in the studies above showed that
Nevertheless, compressive modulus values of the B value in the equation above varied between
all scaffold types are summarized in Table 3. 5 and 9 for different ceramic materials and pore
Although the values are significantly less than shapes [43-46] . This model was adopted for structures
the human trabecular bone elastic modulus (~10 with basic pore shapes of oblate, elliptical, and
[47]
GPa), the values are similar to or slightly lower spherical . Although the equation was developed
than that of a rat calvaria (1.5 – 4 GPa) [39-41] . for nonrandom porous mullite ceramic parts,
Regression models have been proposed to it was reported that the compressive strength
estimate the strength of a porous ceramic part of ceramic lattice structures fit the model with
based on the void shape [42-45] . Duckworth first independent modification of either the pore shape
proposed the exponential dependence of relative or the pore size . In our current study, scaffolds
[46]
strength using the equation below : had an open lattice structure and pores were highly
[44]
88 International Journal of Bioprinting (2020)–Volume 6, Issue 2