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Materials Science in Additive Manufacturing LPBF of Mg and its bio-applications

However, their elastic modulus and mechanical strength Figure 1. The development of Mg-based implants has gone
are much higher than natural bone, which cause the “stress through two stages, with the 21 century as the dividing
st
occlusion” effect after implantation, thus leading to the line. Before the 21 century, Mg alloys were mainly used in
st
[23]
atrophy of natural bone tissue and even migration failure . bone fixation devices. In 1900, Payr et al. pioneered the
[5]
Moreover, they might release some toxic metal ions, which use of Mg as a bone connector for the fixation of injured
induce inflammation. Unfortunately, the implants do bone, and the Mg plate produced no adverse effects in
not easily degrade, and thus, they need to be removed in animals. In 1906, Lambotte extended the animal in vivo
secondary surgery after implantation . In this case, this experiment to a human clinical study, using Mg plates and
[6]
[24]
could the patients will undoubtedly have to endure huge steel nails to fix the calf fracture of patients . Still, the
pain and shoulder extra economic burden. Therefore, it Mg plate and steel nails formed galvanic corrosion, which
is imperative to develop new metal scaffolds for repairing produced a large amount of hydrogen. The implantation
bone defect . site appeared to have a gas swelling phenomenon. In
[7]
1938, McBride et al. used a bone fixation device made
[25]
Recently, biodegradable metals such as magnesium of Mg-Al-Mn alloy to treat multiple fractures, and no
(Mg), zinc (Zn), and iron (Fe) alloys have become negative effects were observed in the fracture tissue after
a hot research topic in tissue repair because of their implantation. However, due to the rapid degradation rate
mechanical strength, unique degradation properties, of Mg alloy in the human body, the clinical research of
and good biocompatibility [8,9] . After implantation, these Mg alloy as a bone fixation device has stalled in the late
biodegradable metals have the sufficient mechanical 20 century .
[26]
th
strength to provide support during the healing process .
[10]
Importantly, they can be completely degraded in vivo, and Due to the rapid development of science and
st
their degradation products will be metabolized by the technology after the 21 century, some Mg alloy bone
[11]
human body without any toxic side effects . Compared fixation devices have passed clinical trials and obtained
to Zn and Fe alloys, Mg alloy has received wide attention regional certification. In 2008, the United States
from experts and scholars since it has the following three established a research center to study biodegradable
significant advantages: biomaterials. In 2013, Syntellix AG successfully developed
degradable Mg alloy screws, which passed clinical trials
(i) Mechanical compatibility. Mg alloy is a light alloy with and obtained CE certification . In 2014, the China Food
[27]
low density and high specific strength. Its density (1.8 and Drug Administration certified the Mg-Zn-Ca bone
– 2.1 g/cm ) and elastic modulus (40 – 45 GPa) are nail developed in South Korea because of its relatively
3
similar to those of human bone, indicating that they slow degradation rate . In recent years, Mg alloys have
[14]
can effectively reduce the stress shielding effect [12,13] . gradually been used to manufacture cardiovascular and
It has excellent application prospects in bone tissue tissue engineering scaffolds. Chaya et al. used Mg bone
[28]
defect repair. plates and screws and titanium alloy plates and screws
(ii) Biodegradability. The standard electrode potential of to repair bone cracks in rabbits. The results showed that
Mg is −2.37 V. Mg alloy can completely degrade the the degradation of Mg bone plate was beneficial to bone
body by self-corrosion. The degradation products have healing. Zhao et al. used Mg screws to fix vascularized
[29]
no apparent side effects on the human body and can bone grafts with femoral head necrosis and found that
be excreted through human metabolic processes [14,15] . released Mg ions could stimulate the generation of fresh
(iii) Biocompatibility. Mg, which is involved in synthesizing bone. Wang et al. used Mg-Zn-Y-Nd alloy scaffolds to
[30]
a variety of proteases and nucleic acids, is one of the treat esophageal cancer. The data showed that Mg alloy had
essential nutritional elements for humans. Mg ion is good biocompatibility and degradation performance and
conducive to the dilatation of blood vessels and the could kill the esophageal cancer cells.
healing of bone tissue. Therefore, biodegradable Mg
alloy is hailed as the new-generation medical metal 1.3. Advantages of laser powder bed fusion (LPBF)
materials. The comparison between Mg alloy and for the fabrication of implants
other bone implants is shown in Table 1. To meet the requirements of clinical applications, bone
implants should possess not only appropriate mechanical
1.2. Development of Mg-based implants
strength and good biocompatibility but also personalized
Mg and its alloys, as the promising implants, are mainly shape to match different damaged parts. The traditional
used in bone fixation devices, cardiovascular scaffolds, preparation methods of Mg alloy components are mainly
and tissue engineering scaffolds [20-22] . The advantages of casting and powder metallurgy. Although the formed
Mg implants and its clinical applications are presented in Mg alloy components have good mechanical properties,

Volume 1 Issue 4 (2022) 2 https://doi.org/10.18063/msam.v1i4.24