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Zhang, et al.

Figure 14. Optical microscope images of Goldner’s staining and non-decalcified sections after being porous-titanium-implanted for 28, 56,
and 84 day (Reprinted from Transactions of Nonferrous Metals Society of China, 29(12), J. Zheng, L. Chen, D. Chen, et al., effects of pore
[88]
size and porosity of surface-modified porous titanium implants on bone tissue ingrowth, 2534–2545, Copyright (2019), with permission
from Elsevier).

as shown in Figure 15. Two pore shapes of NiTi have delay pore blockage. Combining pores of different shapes
similar Young’s modulus (rectangular pores 1.38 GPa and taking advantage of their respective advantages may
spherical pores 1.98 GPa), but the spherical pore NiTi has be a potential design direction in the future.
higher compressive strength (rectangular pores 68 MPa and
spherical pores 107 MPa). The increase in compressive 3.5. Interconnectivity
strength attributes to the spherical shape, which significantly Earlier researches have shown that porous implants
avoids the stress concentration. The sharp edge provides a must have interconnected pores to provide space for
location for crack initiation during the deformation process, the vascular tissue required for continuous mineralized
and the elimination of stress concentration can generate bone ingrowth . Otsuki et al. considered that the
[95]
[94]
more energy absorption before fracture . interconnection of pores is a critical factor in bone
[91]
According to Bael et al. , when the scaffold ingrowth, and properly interconnected pores can promote
[72]
was cultured in growth medium without osteogenic bone ingrowth and differentiation.
differentiation inducer, only the triangular unit cell scaffold Zheng et al. reported that the degree of bone
[88]
with a pore size of 500 μm had significantly increased ALP ingrowth of implants with a porosity of 30% (A30) was
activity. According to Reilly and Engler , in addition lower than that of A40 and A50 implants. It is mainly
[92]
to growth factors, mechanobiological stimulation in the due to the different blood vessel formation degrees,
scaffold structure can also promote cell differentiation. which is essential for bone formation . The degree of
[53]
The authors speculated that the pore size would affect formation of blood vessels with a pore size >400 μm
the perception of the environment, and the cells will feel increased significantly. In terms of angiogenesis, A40
various stimuli from different pore sizes on the surface . and A50 implants have more advantages than A30
[93]
For triangular pores with smaller pore sizes, sharp angles implants, indicating that suitable pore size and good
with restricted pore sizes, in which cells can attach to interconnectivity are essential for bone and vascular
different structs, leading to cell differentiation. Bael et tissue ingrowth. An adequate blood supply is necessary
al. also believed that triangular pores might benefit cell for a good combination of bone and porous implants . In
[96]
[72]
proliferation and differentiation, while circular pores can addition to providing nutrition, the capillaries in the bone

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