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International Journal of Bioprinting The biological properties of WE43 scaffolds via the oxidative heat strategy

very important to find a more suitable bone substitute. oxide to the metal consumed to create the metal oxide. A
Some artificial bone materials, such as calcium phosphate PBR less than 1 indicates that the metal oxide has weak
and calcium sulfate bone cements, can fill bone defects passivation, while a PBR larger than 2 indicates that the
but lack biological activities, e.g., osteoinduction and oxide is easily peeled off and that the passivation is poor.
durable mechanical support . External fixator distraction When the PBR is greater than 1 and less than 2, the metal
[3]
osteogenesis can repair defects of the diaphysis of the oxide has a significant passivation effect and may create a
extremities, but the repair may take a long time and it protective layer to prevent corrosion of the matrix metal.
is difficult to repair the metaphysis due to anatomical The oxidation of magnesium can generate MgO with a PBR
mismatch . In recent years, 3D printing technology has of 0.81, which cannot slow its degradation rate , while the
[4]
[16]
been used to prepare medical implants and biological PBR values of Nd O , Y O and Gd O are 1.0584, 1.1923,
2
3
3
2
2
3
organs , which can make prostheses personalized to the and 1.29, respectively [17,18] . Moreover, Y, Nd, and Gd are
[5]
patient, achieve good anatomical shape matching, and more reactive than Mg, so they preferentially react with
control the elastic modulus by adjusting the printing oxygen at high temperatures, forming a thin oxide layer on
parameters (structures, porosity, etc.) to repair large- the surface. At present, microarc oxidation and phosphate
segment bone defects and achieve the desired clinical coating of magnesium alloys have been widely studied,
effect [6,7] . However, currently, 3D printing still uses Ti6Al4V which can indeed significantly slow down the degradation
as the main component. Due to its nonabsorbability, the rate of magnesium alloys [19,20] . However, the complicated
relative stability between bone and prosthesis and the long- process requires the use of specific instruments. For porous
term effects of stress conduction are uncertain and remain structures, it is not easy to use microarc oxidation to
to be observed [8,9] . A bone defect filling material with overall uniformly modify the surface of prostheses. In our previous
strong support, osteoinductive ability, and biodegradability studies , oxidation heat treatment is a very cost-effective
[21]
over time is urgently needed in the treatment of bone and simple passivation method. Under a high-temperature
defects in limbs with 3D-printed prostheses. oxidizing atmosphere, the degradable magnesium alloy
Among biodegradable bioactive metals, magnesium undergoes a controllable oxidation reaction, and on the
and magnesium alloys have broad application prospects surface, a thick layer of passivation will eventually develop,
in orthopedic repair and reconstruction. The compression which effectively isolates magnesium alloy and body fluid
screw MAGNEZIX® developed by Syntellix AG, with and slows the degradation rate of magnesium alloy medical
[22]
the magnesium alloy WE43 as the main component, has implants in a body fluid environment . However, no
been successfully applied in clinical practice, e.g., fracture literature has investigated the effects of thermal oxidation
fixation, and it presents biodegradable and osteogenic treatment on the biocompatibility, and osteogenic
properties . Magnesium is an element that is required for properties of magnesium alloys. Therefore, in this work,
[10]
the proper functioning of the human body and is involved thermal oxidation-treated WE43 magnesium alloy and
in a large variety of different biological processes. The as-printed WE43 were used to explore the differences in
beneficial role of magnesium ions in the development of biocompatibility and osteogenic properties.
bone has been proven in a number of in vivo and in vitro
studies, and it has been found that magnesium alloys can 2. Materials and methods
increase the expression of alkaline phosphatase (ALP) 2.1. Scaffold manufacturing and oxidation
in osteoblasts [11-13] . For example, Li et al. showed that the heat treatment
number of osteoblasts around magnesium alloy implants The scaffold was facilitated with laser powder bed fusion
was significantly increased compared to the number (L-PBF) using a compact L-PBF machine (BLT S210,
around titanium implants . He et al. used different China). The WE43 powder was prepared using centrifugal
[14]
concentration gradients (0–3 mM) of magnesium ions atomization (Tangshan Weihao, China). The powder was
to culture human osteoblasts in vitro and found that the composed of 3.87% Y, 2.24% Nd, 1.16% Gd, 0.39% Zr, and
proliferative and osteogenic effects of magnesium ions on residual Mg (in mass). The scaffolds were created with a
osteoblasts increased with increasing concentration . pore size of 800 μm and a porosity of 60.0% as per design.
[15]
However, the rapid degradation rate of WE43 The scaffold manufacturing protocol has been reported
[23]
magnesium alloy is a hindrance to its clinical application. previously . The scaffolds used in our experiments were
Whether the oxide generated by metal oxidation can cylindrical with the sheet gyroid structure and the strut
reduce the pace of WE43 magnesium alloy deterioration size is 600 μm. The size was Ф10 mm × 10 mm. A 1-h
depends on the Pilling–Bedworth’s ratio (PBR). PBR is preheating at 200°C was performed on the WE43 powder
used to quantify the passivation impact of metal oxides, bed before the melting process. The processing chamber for
which is defined as the volumetric ratio of the surface the L-PBF process was filled with argon that had a purity

Volume 9 Issue 3 (2023) 95 https://doi.org/10.18063/ijb.686