Page 106 - IJB-8-3

Rare Earth Magnesium Alloy
the influence of shape on properties, all samples in this time and ΔV (mg) was the weight loss of the specimen.
work were cubic shape. A (cm ) was the surface area and t (day) was the
−2
The microstructure of SLM processed specimens immersion time. The scanning electron microscopy
was captured by optical microscopy (OM, DM4700, (SEM, EVO 18, Zeiss, Germany) combined with
Leica, Germany), and the phase identification was EDS was adopted to observe the degradation surface.
performed by XRD. Before OM observation, the The pH was recorded by a pH meter (pH, FE20K,
surfaces of the samples were treated by the standard for Mettler FiveEasy, Switzerland), and the Mg and Sc ion
metallographic examinations. concentrations were detected by an inductively coupled
plasma atomic emission spectrometry (ICP-AES, Optima
2.3. Electrochemical measurements 7000DV, Perkin-Elmer, Germany).
The samples with a dimension of 1 × 1 × 1 cm were 2.5. In vitro biocompatibility
3
prepared for electrochemical tests. Before testing, a wire
was soldered to the back of the specimen, and epoxy resin The BMSC cells were adopted to assess the in vitro
was used for inlay so as to expose only 1 cm of working cytocompatibility of Sc-containing Mg alloys. Before
2
surface. Then, the samples were grounded with SiC the experiment, the cells were cultured in Dulbecco’s
papers and polished with 0.05 μm water-soluble diamond Modified Eagle’s Medium (DMEM), containing 10%
polishing paste. In this study, the electrochemical tests were fetal bovine serum, 100 U/mL penicillin, and 100 mg/
performed on an electrochemical workstation (PARSTAT mL streptomycin. In addition, the samples were soaked
4000A, Princeton Applied Research, Princeton, NJ, USA), in DMEM. The extracts medium was obtained by indirect
which was equipped with a conventional three-electrode contact method based on ISO 10993-5:1999. Then, the
cell system. The saturated calomel electrode was applied extracts were diluted to 50% and 10% concentration,
as the reference electrode, whereas the platinum electrode respectively. The cells were transferred to a 48-well
and the specimen served as counter electrode and working cell culture plate with a density of 5000 cells/400 μL
electrode, respectively. Before the potentiodynamic medium in a well. The culture medium was replaced
polarization and electrochemical impedance spectroscopy by 100%, 50%, or 10% extraction. After seeded 1, 4,
(EIS) tests, an open circuit potential (OCP) test was and 7 days, the fluorescent staining and Cell Counting
performed in the simulated body fluid (SBF, 37°C, pH 7.4) Kit-8 (CCK-8) assay were employed to assess the cell
for 20 min to reach a steady value. The potentiodynamic viability and cells proliferation, respectively. The stained
polarization sweep rate was 1 mV/s. The polarization cells were mounted onto glass slides and observed using
curves were fitted and analyzed by CView 3.10 software. a fluorescence microscopy (BX60, Olympus, Japan)
The AC impedance test frequency scope was 100 k ~ (n = 1). The absorbance was measured at 450 nm using a
0.01 Hz, and the amplitude was 10 mV. spectrophotometer.
2.4. Immersion tests 2.6. Statistical analysis
Immersion tests were carried out in SBF with an In this study, multiple replicate tests were performed for
exposure ratio of 20 mL/cm . The degradation rate could each group of samples and the final experimental results
2
be estimated by the hydrogen evolution rate. The resin were expressed as mean ± standard deviation. It was
encapsulated sample was placed in an inverted funnel regarded to be statistically significant only when P < 0.05.
to avoid the escape of hydrogen gas during degradation.
Then, a 25 mL burette was inverted above the funnel to 3. Results and discussion
record the volume of released hydrogen. After immersion, 3.1. Microstructural feature of milled powder
specimens were washed using a solution containing
20% CrO and 1% AgNO so as to clean the corrosion The phase evolution of Mg-25Sc powder was investigated
3
3
product. The degradation rates were calculated by the by XRD, with collected spectrum depicted in Figure 1A.
hydrogen evolution volume (P ) and weight loss (P ), Before milling, clear crystalline peaks corresponding
H
W
respectively. The calculation formula was as follows : to hexagonal close-packed Mg and Sc phases were
[35]
observed. After milling for 10 and 20 h, the Mg peaks
∆ V
P = 2 006. At (1) turned relatively broad and weak. Meanwhile, the Sc
H
peaks inclined to disappear. Furthermore, only α-Mg
∆ W peaks were detected after milling for 40 h. Besides, the
P = 210. (2)
W
At diffraction peak of α-Mg(101) evidently shifted to low-
angle region, as shown in Figure 1B. It was indicated
Where, the ΔV (mL) was the total volume of that Mg(Sc) solid solution powder was prepared after ball
hydrogen gas generated during the whole immersion milling for 40 h.
98 International Journal of Bioprinting (2022)–Volume 8, Issue 3