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International Journal of Bioprinting 3D-printed biodegradable metals for bone regeneration

printing methods for magnesium and magnesium alloys The remaining methods, such as atomic layer deposition
mainly include PBF, ME, BJ, and 3D weaving. 3D-printed (ALD), magnetron sputtering, or sandblasting, may delay
regenerated magnesium phosphate implants can ensure degradation while decreasing biocompatibility as well as
the stability and recovery of hip joint dysplasia, and cracking and uneven degradation. 148,149
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3D-printed polycaprolactone/magnesium porous scaffolds The addition of other elements and the choice of
can promote bone defect repair in the early stages and have different manufacturing methods can also improve the
good cell compatibility. Porous 3D-printed Mg Nd Zn Zr properties of alloys. For example, the addition of aluminum
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(referred to as JDBM) implants possess good mechanical to zinc-based alloys enhances the antimicrobial activity
properties, are compatible with MC3T3-E1 and RAW267.4 of the components, but aluminum is also cytotoxic and
cells, and prevent implant infections. 134 may cause inflammation. 150,151 The addition of titanium,

4.2. Zinc and its alloys copper, magnesium, manganese, lithium, and other
While pure zinc has a low tensile strength (20 MPa) and metal elements to zinc can delay component corrosion.
is usually not used in the manufacture of implants, zinc Currently, the most studied zinc-based alloys are Zn–xMg
alloys can achieve tensile strengths of 200–600 MPa, which and Zn–xAl alloys, which, when prepared by appropriate
satisfy the requirements for bone implants. 16,135,136 The main fabrication methods, such as plasma sintering (MASPS)
advantage of zinc alloys is that their biodegradation rate to control the porosity of the components, can improve
the mechanical properties while reducing the degradation
is between that of magnesium- and iron-based alloys and rate. 152-154 Zn–Mg alloy scaffolds have great potential in
is closest to the ideal biodegradation rate; this allows zinc the treatment of load-bearing bone defects. On the one
alloys to provide effective support for bone defect healing hand, zinc and magnesium play important roles in bone
before complete degradation and to avoid secondary metabolism and are conducive to cell proliferation and
damage from stress interruption after healing. Second, zinc bone tissue regeneration; on the other hand, Zn–Mg alloys
ions are involved in bone formation and mineralization and can avoid the production of hydrogen gas, severe pH
can accelerate bone defect healing by activating Runx2 and fluctuations, and rapid corrosion after injection. Moreover,
Osterix to promote osteoblast differentiation, inhibiting Mg is added to the Zn matrix to provide nucleation
RANKL to reduce osteoclastogenesis, and promoting sites and promote the production of secondary Mg2Z11
citrate deposition. 137-139 Zinc also has a proangiogenic phases, leading to grain refinement and strengthening.
effect, which guarantees good blood circulation during The synergistic effect of solid solution strengthening and
bone regeneration. Moreover, zinc has strong antimicrobial precipitation strengthening endows Zn–Mg alloys with
activity with some anti-infective effects, providing a stable unique advantages in the treatment of orthopedic diseases,
immune microenvironment for bone regeneration. 140 helps avoid chronic inflammatory reactions caused by
The disadvantages of zinc include its low biocompatibility permanent implantation, and removes the need for
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and high manufacturing difficulty. Excessive release of additional surgeries. At present, scholars have focused
zinc ions during degradation results in cytotoxicity and mainly on the mechanical properties, wear resistance,
attenuates osteoblastic activity, decelerating the healing fatigue resistance, corrosion resistance, degradation
of bone defects. 141-144 Furthermore, zinc has a lower behavior, microstructure, and other directions of Zn–
melting point than magnesium, and although zinc does Mg alloys. By introducing specific metals or nonmetal
not react with air, it is difficult to convert into porous elements, improving preparation methods, programming
structures due to vaporization and sputtering during degradation behavior, etc., Zn–Mg alloys can be modified
processing. 145,146 Retarding the corrosion of zinc-based to improve their bone regeneration potential. 156,157
alloys by surface modification, adding different elements Magnesium–zinc alloys are the most biocompatible,
or improving the alloy manufacturing process can improve and the mechanical properties of these alloys can be
the properties of these alloys. Surface modifications such significantly improved by adjusting the Zn–Mg ratio. The
as microarc oxidation (MAO) can regulate the oxidation Mg–Zn alloy components molded by hot extrusion using
of zinc and improve its biocompatibility, but there is still a casting process have a low degradation rate and good
a certain degree of cytotoxicity, and the degradation rate mechanical strength. However, whether the alloy phase
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is far greater than that of pure zinc, deviating from the of a component is uniformly distributed has an important
ideal biodegradation rate. Additionally, biomimetic impact on its mechanical properties and corrosion form,
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deposition can improve biocompatibility. Immersing the and if a uniform distribution cannot be achieved during
components in SBF solution for 14 days can result in the the manufacturing process, the component may suffer
formation of a protective layer of corrosion products, which from mechanical strength degradation, localized pitting
can delay corrosion and improve cytocompatibility. corrosion, and other problems. 159-162 However, how to
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Volume 10 Issue 3 (2024) 47 doi: 10.36922/ijb.2460