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Zhang, et al.

Figure 11. Millimeter-level pores in novel gyroid lattices . (Reprinted from Journal of Material Science & Technology, 62, P. Wang, X.
[75]
Li, S. Luo, et al., additively manufactured heterogeneously porous metallic bone with biostructural functions and bone-like mechanical
properties, 173–179, Copyright (2021), with permission from Elsevier).

A B ∏ 1 ρ = − scaffold /ρ material (1)

In which ρ is the density of material itself, and
material
ρ scaffold is the apparent density of the scaffold measured
by dividing the mass of the scaffold by the volume of the
scaffold .
[65]
The type of bone in-growth depends on the pore size
and porosity. Larger pores are conducive to direct bone
C D formation because they allow blood vessel formation
and hyperoxygenation, while smaller pores lead to
osteochondrosis . However, the mechanical properties
[86]
and degradation rate determine the upper limits of pore
size and porosity.
The intrinsic properties of a material, porosity,
and processing methods can determine the mechanical
Figure 12. Basic single unit and computer-aided design of porous- properties of porous implants. As the material and
surfaced titanium plates. (A) A single unit of diamond crystal processing method fixed, the porosity cannot be so
lattice. (B) P300. (C) P600. (D) P900 (Reprinted from Materials
[80]
Science and Engineering: C, 59, N. Taniguchi, S. Fujibayashi, M. high that it cannot meet the mechanical performance
Takemoto, et al., effect of pore size on bone ingrowth into porous requirements. Scaffolds made of biomaterials with
titanium implants fabricated by additive manufacturing: An in vivo high degradation rates should not have high porosity
experiment, 690–701, Copyright (2016), with permission from (>90%) because the rapid consumption of biomaterials
Elsevier). will damage their mechanical and structural integrity .
[87]
In contrast, scaffolds made of biomaterials with low
(П) is measured and calculated by the gravimetric degradation rates and robust mechanical properties can
method , as the following equation be highly porous.
[85]

International Journal of Bioprinting (2021)–Volume 7, Issue 2 23