Page 422 - IJB-9-5

International Journal of Bioprinting 3D-printed Mg scaffolds promote bone defect repair

degradation rate of 3D-printed Mg alloy scaffolds in vitro we loaded ZA into the ceramic composite coating on the
from 11.60 ± 0.05 mg/day to 2.47 ± 0.45 mg/day, which is surface of 3D-printed Mg alloy scaffolds and promoted
only about 21% of the original rate, greatly improving the the healing of osteoporotic bone defects through the joint
corrosion resistance of 3D-printed Mg alloy scaffolds. The action of Mg ions released from the degradation of Mg
calcium phosphate material commonly used for Mg alloy alloy scaffolds and ZA loaded on the coating. In view of the
surface coatings could only reduce the degradation rate of obvious adverse effects of ZA in systemic application and
JDBM Mg alloy bars to 72% of the original rate , and the the small effect of the drug on local lesions [29,30] , we adopted
[22]
protective effect of the coating on the Mg alloy substrate the method of combining scaffold implantation with local
was significantly weaker than that of a polysilane ceramic drug delivery. ZA was added to the coating material to
coating. coat the surface of the scaffolds, and the drug was released
We found that when the Mg-based implant degraded slowly and controllably with the degradation of the scaffolds
too quickly, a high concentration of Mg ion simultaneously to achieve local controlled release and slow release of the
inhibited the proliferation and differentiation of osteoblasts drug. In vitro drug release experiments showed that ZA
and osteoclasts. These results are consistent with those of was released stably from the scaffold surface at a relatively
previous studies showing that alkaline microenvironments low rate, and the release rate reached 54% within 30 days,
with high Mg ion concentration as a result of Mg degradation indicating the sustained release of the drug. When the Mg
can inhibit new bone regeneration and absorption [23,24] . alloy scaffolds were degraded, ZA loaded on the coating was
Therefore, it is necessary to adjust the degradation rate of released slowly and acted directly on the defect area with Mg
Mg alloys to release an appropriate amount of Mg ions to ions at the same time. The results showed that ZA released
promote osteogenesis. Some studies have shown that a Mg from the coating during degradation did not affect the effect
ion concentration of approximately 2 mM promotes the of Mg ions on osteogenesis, but it significantly inhibited
proliferation and differentiation of osteoblasts in vitro and active osteoclast differentiation and bone resorption in
formation of new bones in vivo . The effect of osteogenic rats with osteoporosis by inhibiting osteoclast formation,
[25]
induction is best when the concentration of Mg ions is in the downregulating the expression levels of osteoclast-related
range of 2.5 to 5 mM . However, when the concentration genes and subsequently increasing bone density and bone
[26]
of Mg ions is more than 10 mM, it will begin to inhibit the strength. The results of this study suggest that combining
osteogenic differentiation. When the concentration of Mg ion the osteogenic effect of Mg with the inhibitory effect of ZA
exceeds 20 mM, it will even lead to a significant increase in cell on osteoclasts can improve the dynamic balance between
apoptosis. The in vitro degradation experiment showed that bone formation and resorption in the local environment
the concentration of Mg ions produced by the 3D-printed Mg and promote repair and reconstruction of osteoporotic
alloy scaffolds in the ceramic coating group in the early stage bone defects.
of degradation was approximately 2.5 mM, and then slowly In addition, the effect of hydrogen produced by the
increased to 10 mM. After implantation, because of absorption degradation of Mg alloys must be considered. Hydrogen
in the peripheral blood circulation, the concentration of Mg is an important degradation product of Mg. When the
ions in the implantation area is often lower than the in vitro degradation rate of Mg alloy implants in vivo is too rapid,
degradation concentration in the same period . Therefore, the hydrogen produced cannot be absorbed by the body
[27]
it can be speculated that ceramic-coated Mg alloy scaffolds in time and accumulates in the implanted area to form a
implanted into the body form a microenvironment in which subcutaneous cavity. The rapid accumulation of hydrogen
the concentration of Mg ions is less than 10 mM, which is delays bone healing, forms obvious tissue calluses, blocks
conducive to osteogenic differentiation. The released Mg blood flow, and leads to tissue necrosis . Therefore, it is
[31]
ions can upregulate expression of osteogenic-related genes, necessary to adjust the degradation rate of Mg alloys to
promote the proliferation and differentiation of osteoblasts, reduce hydrogen production. Although a large amount
and accelerate the growth of new bone in the bone defect. of hydrogen has adverse effects on patients, hydrogen,
The future research goal is to achieve a precise match between as an important pathophysiological regulator, has great
the scaffold degradation rate and the bone growth rate by potential to regulate oxidative stress, inflammation, and
adjusting the coating thickness, which will lead to complete apoptosis . Hydrogen not only reduces oxidative stress by
[32]
repair of the defect when the scaffold is completely degraded. directly reacting with strong oxidants, but also indirectly
The number of BMSCs involved in bone repair and reduces oxidative stress by regulating the expression of
their differentiated osteoblasts in patients with osteoporotic various genes . In this study, the detection of ROS in
[33]
bone defects decreased, and their function was low, while osteoclasts showed that the average fluorescence intensity
the osteoclasts were abnormally active, resulting in slow of ROS in the Mg alloy group was significantly lower
rate and prolonged time of defect repair . Based on this, than that in the control group, demonstrating that the
[28]

Volume 9 Issue 5 (2023) 414 https://doi.org/10.18063/ijb.769