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Zhang, et al.

A B

Figure 29. (A) Internal friction (tan δ) of layered and rolled NiTi at 1 Hz oscillation frequency, (B) temperature dependence of tan δ and
[9]
Young’s modulus of layered NiTi at 90 kHz oscillation frequency (Reprinted from Scripta Materialia, 146, X. Wang, M. Speirs, S.
Kustov, et al., selective laser melting produced layer-structured NiTi shape memory alloys with high damping properties and Elinvar effect,
246–250, Copyright (2018), with permission from Elsevier).

Figure 30. Characterization methods of additive manufacturing-NiTi implants.

must meet both mechanical and biological performance pore sizes and pore shapes to form a bio-mimetic structure
requirements. As a consequence, the design of the porous is a promising direction [114] . Research on superelasticity,
structure and the mechanical properties are of vital phase transformation behavior, and texture development
importance. It mainly focuses on the porous structure design of porous SLM-NiTi scaffolds are far from enough [131] .
and mechanical properties, and the characterization methods Furthermore, we can combine machine learning with 3D
required for AM-NiTi products are also summarized. bioprinting to improve part quality [132] , design novel 3D
However, there are still many challenges to face. The models [133] , and establish unified frameworks to share
SLM process is complicated, making the microstructure of data sets [134] and ML models [135] among the research
SLM parts very different from traditionally manufactured community.
samples [122] . The mechanism of the SLM process affecting
the microstructure of parts has not been clarified. Acknowledgments
Moreover, the design of functionally graded porous
structures still needs further research. Bael et al. have This research was funded by the National Natural Science
[72]
conducted a series of researches on the unit cell design, but Foundation of China (no. 51831011, no. 31971246, and
it is still not enough, and more novel unit cell designs are no. 52011530181) and Shanghai Science and Technology
needed. Taking into account the combination of different Project: 20S31900100. Medical engineering cross

International Journal of Bioprinting (2021)–Volume 7, Issue 2 35