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Zhou, et al.
inhibition efficiency for laser processed Zn implant the processing defects related to LPBF such as pore
reaches 34.28% . In fact, the released Zn ions can formation, crack, oxidation, and residual stress should be
[79]
be adsorbed to the bacteria surface by Coulomb force, further studied. Effect of multi-alloy elements in Zn matrix
which interferes with cell wall synthesis, thus leading to on the formation quality also deserves attention. A fact
the loss of cell wall integrity [171] . On the other hand, once is that LPBF of Zn is a very complex non-equilibrium
Zn ions penetrate the cell wall, it can replace the cation metallurgical process, which involves physical processes
position of the cell membrane, thereby destroying the cell such as melting, evaporation, solidification, and solid-
membrane metabolism and structure [172] . However, the state phase transformation. The composition, structure,
antibacterial effect of Zn ion is limited. Till now, Cu, Ag, and properties of materials have changed dramatically.
and Ce that possessed powerful antibacterial effect were From this aspect, it is still necessary to clarify the basic
added into Zn-based implants [79,173,174] . One concern is that theory of laser manufacturing Zn metal and realize the
the addition of these alloying elements may reduce the additive manufacturing process with high reliability, high
biocompatibility of Zn implants to a certain extent, since precision, and high flexibility.
they have lower tolerance than Zn in the human body. (3) Porous scaffolds possess high specific surface
Furthermore, the reports on the LPBF of antibacterial area, which leads to relatively high degradation rate
Zn-based implants are in the form of multiple powder compared with the bulk samples. In this case, the gradient
mixtures, such as Zn powder and Nd powder. It is difficult structure, topology structure, material design, or special
to ensure the microstructure uniformity of as-built parts. surface modification of LPBF-prepared Zn porous
From this point of view, it is necessary to develop special scaffolds need to be studied, aiming to keep mechanical
antibacterial Zn-based functional powder for LPBF. integrity during reconstruction. In addition, Zn-based
implants with interconnected pores provide necessary
6. Remarks and perspectives growth space for ingrowth of tissue cells. Considering
LPBF is regarded as an ideal process for the fabrication this factor, the effect of porous scaffolds with different
of Zn implants, since it can precisely control the inner structures on biocompatibility deserves attention. Great
porous structure and outer complex shape. The resulting numbers of in vitro studies for LPBF-fabricated Zn-based
formation quality and properties including mechanical implants have highlighted promising result. However, the
and degradation of LPBF-processed Zn implants are assessment and mechanism of the biological interactions
decided by the powder properties, processing, design, between released Zn ions and other ions still lack related
and chemical component. Although great progress has in vivo studies. Therefore, comprehensive tests using
been achieved in understanding and optimizing the various animal models and implant locations should be
LPBF-processed Zn in the last several years, the current performed in the future work.
development is still in the infancy stage as compared with
other biomedical metal. Therefore, to realize the clinical Acknowledgments
application of LPBF-processed Zn, a considerable amount This study was supported by the following funds:
of researches are necessarily considered in the future. (1) Anhui Provincial Natural Science Foundation
(1) The implants require the metal materials to (2008085ME149); (2) Anhui Provincial Top Academic
provide appropriate mechanical properties, suitable Aid Program for Discipline (Major) Talents of Higher
corrosion rate and excellent biocompatibility, as well as Education Institutions (gxbjZD2020087); (3) Anhui
biological activity in human body. Usually, the mechanical Provincial Natural Science Research Key Program
and degradable performances are strongly decided by the of Higher Education Institutions (KJ2020A0693,
microstructure, which results from alloy composition KJ2020A0700); (4) Academic Leader and Backup
design, element selection, and process parameters. At Candidate Research Project of Tongling University
present, the Zn powder used for LPBF is developed based
on the traditional manufacturing process. During LPBF of (2020tlxyxs02, 2020tlxyxs04); (5) Key Laboratory
Zn-based metal, the chemical composition usually varies of Construction Hydraulic Robots of Anhui Higher
Education Institutes, Tongling University (TLXYCHR-
due to the metal evaporation. As a result, the chemical O-21YB01); (6) Jiangxi Key Laboratory of Forming
composition of the final parts may deviate far from the
composition of the initial powder, which may have an and Joining Technology for Aerospace Components,
important impact on its microstructure and properties. Nanchang Hangkong University (EL202180264); and
According to the requirements of clinical performance, (7) Jiangsu Key Laboratory of Precision and Micro-
the development of specialized Zn-based powder for Manufacturing Technology.
LPBF is an urgent issue to be addressed. Conflict of interest
(2) Although the microstructure and formation
quality of Zn metals have been preliminarily studied, The authors declare no known conflicts of interest.

International Journal of Bioprinting (2022)–Volume 8, Issue 1 87