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

Table 2. Advantages and disadvantages of biodegradable metallic materials
Materials Advantages Disadvantages Mainstream 3D Common alloys Implants Applications References
printing
technologies
Magnesium Density and Young’s Excessive PBF, ME, BJ, 3D Magnesium Magnesium Osteoarthritis 23,111-113,116-
and its modulus close biodegradation weaving phosphate, phosphate of the hip, 118,127-130,132-134
alloys to those of bone rate, hydrogen polycaprolactone/ implant, oral implant,
tissue, magnesium precipitation and magnesium, Mg– JDBM bone defect
ions promote alkalization during Nd–Zn–Zr alloys implant repair,
osteogenesis and degradation osteoporosis
vascularization bone defect
Zinc and its Moderate Low biocompatibility PBF, DED, BJ ZnO, ZnO- Implants Oral implant, 137-146,165
alloys biodegradation rate, with cytotoxicity, AgHAP, Zn–xMg modified antimicrobial
zinc ions promote high manufacturing alloys with zinc coating
bone formation and difficulty, uneven coating
vascularization, alloy phase causing
good antimicrobial pitting, low
activity mechanical strength
Iron and its High tensile Low degradation L-PBF, BJ Fe–Mn–Ca/Mg, Fe–Si Bone defect 46,47,49,166-168,181-
alloys and mechanical rate, high modulus Fe–Mn, Fe–Si implant repair 183
strength, excellent of elasticity,
biocompatibility, degradation produces
low cost nonmetabolizable
iron oxides
Abbreviations: BJ, binder jetting, DED, direct energy deposition; L-PBF, laser powder bed fusion; ME, material extrusion; PBF, powder bed fusion.

neuronal cells, which in turn promotes the osteoblast bone defects in the patient. 72,121 When other substances
proliferation and neovascularization and accelerates the are added to magnesium to form magnesium alloys, the
healing of bone defects. 23,113 By converting magnesium corrosion precipitation of the alloying elements (e.g.,
components into porous structures, the voids in the Al and Mn) may be cytotoxic, and the proportion of the
components can support the growth of mineralized tissues, alloying elements added will affect the corrosion rate of
and the connectivity of the voids can guarantee the flow of the components, which is different for different patients in
nutrients and metabolic waste to the new tissues. 113-115 The the clinic; moreover, the addition of rare earth elements
voids can also be filled with bioactive drugs to promote may be potentially biotoxic to a certain extent, and their
bone regeneration. Considerable experience has been biocompatibility is still uncertain. 116,122,123 Increasing the
achieved in the manufacture of porous magnesium with a purity of magnesium does not cause biotoxicity but has
variety of manufacturing options. 79,80 a limited effect on the magnesium degradation rate. 124,125
Converting building blocks into porous structures is limited
The most significant disadvantage of magnesium
alloys is their rapid rate of biodegradation, which makes by the problems of uneven pore distribution, the presence
of residues, and the high cost of the technology.
80,126
these materials likely to corrode completely before the
patient’s fracture heals; thus, they fail to provide adequate Additionally, the degradation of magnesium in vivo
mechanical support at a later stage, and other means are that occurs via a protocell reaction generates magnesium
required to retard the in vivo degradation of magnesium ions and hydroxide ions, ultimately producing magnesium
alloys. 116-118 To control the rate of magnesium corrosion, hydroxide and hydrogen gas. The magnesium hydroxide
components are usually surface-modified, alloyed, purified, generated by the reaction is loose and does not provide
or converted into porous structures. Specific methods of protection for the components, while the precipitated
surface modification include the addition of coatings and hydrogen creates gas cavities that hinder tissue growth,
nanodiamonds, mesoporous silica (MS), etc. to magnesium and the hydroxide released during the corrosion process
alloys to retard magnesium degradation corrosion. 80,119,120 is also cytotoxic. 127-130 The human body can slowly
Coatings may break down after several weeks or months due absorb precipitated hydrogen and neutralize alkalinity,
to cracking, inhomogeneous degradation, etc., resulting in so delaying the degradation of magnesium is an effective
the loss of coating protection for the component, and the way to prevent gas cavity generation and alkalization.
survival time may not be sufficient to support magnesium For example, Mg–Zn alloys exhibit increased corrosion
alloy implants safely through the recovery period of resistance and reduced hydrogen precipitation and

Volume 10 Issue 3 (2024) 45 doi: 10.36922/ijb.2460