## 3 Results and Discussion
### Discussion  
In this study, we investigated the exposure of various concentrations (1 mM, 5 mM, 10 mM, and 50 mM) of MgO/Mg(OH)\({}_{2}\) NPs in hFOB 1.19 cells to understand in vitro cytotoxicity. The determination of cytotoxicity in response to concentrations of MgO/Mg(OH)\({}_{2}\) NPs in hFOB 1.19 cells will help develop sustainable biodegradable alloys as implant materials for commercial orthopedic devices. A recent study showed that the hemostasis of bone is affected by local pH and oxygen tension [22]. Hypoxia inhibits the proliferation and differentiation of the osteoblast cells responsible for bone formation and stimulates osteoclast cells that are associated with bone resorption. In addition, a foundational study on Mg-based implants reported a faster corrosion rate for implants in the physiological environment of the body, which makes it challenging to establish Mg as a biodegradable material [16]. One study also suggested that the exposure of corrosion products such as MgO to an aqueous solution leads to the formation of Mg(OH)\({}_{2}\)[19]. Further, the corrosion of Mg(OH)\({}_{2}\) in an aqueous solution containing 150 mmol/L of Cl\({}^{-}\) forms magnesium chloride (MgCl\({}_{2}\)) and hydrogen (H\({}_{2}\)) gas [23]. In this study, we observed the presence of trace amounts of Cl for both MgO and Mg(OH)\({}_{2}\) NPs after conducting the immersion test for seven days, as analyzed through SEM-EDX mapping (shown in Figures 7 and 8). This result suggests the formation of water-soluble MgCl\({}_{2}\)-. The presence of Ca and P indicates that these corrosion products might interact with the Ca and P present in the environment and disintegrate in bulk in the case of implant degradation  
Figure 14: SEM results representing the morphological changes in hFOB 1.19 cells in response to various concentrations of Mg(OH)\({}_{2}\) NPs. (**a**) Media Only (-ve control group), (**b**) Cells + Media (-ve control group), (**c**) Cells + Media + 1 mM Mg(OH)\({}_{2}\) NPs, (**d**) Cells + Media + 5 mM Mg(OH)\({}_{2}\) NPs, (**e**) Cells + Media + 10 mM Mg(OH)\({}_{2}\) NPs, and (**f**) Cells + Media + 50 mM Mg(OH)\({}_{2}\) NPs. Figure 13: SEM results representing the morphological changes in hFOB 1.19 cells in response to various concentrations of MgO NPs. (**a**) Media Only (-ve control group), (**b**) Cells + Media (-ve control group), (**c**) Cells + Media + 1 mM MgO NPs, (**d**) Cells + Media + 5 mM MgO NPs, (**e**) Cells + Media + 10 mM MgO NPs, and (**f**) Cells + Media + 50 mM MgO NPs. into the surrounding medium, as explained in the biocorrosion model [24]. These insoluble complex compounds of MgO/Mg(OH)\({}_{2}\) NPs in the form of magnesium phosphates might introduce cytotoxicity into hFOB 1.19 cells, as shown below:  
\[3\text{MgO}+\text{Ca}_{3}(\text{PO}_{4})_{2}\rightarrow\text{Mg}_{3}(\text{PO}_ {4})_{2}+3\text{CaO}, \tag{2}\]  
\[3\text{Mg}(\text{OH})_{2}+\text{Ca}_{3}(\text{PO}_{4})_{2}\rightarrow\text{Mg}_ {3}(\text{PO}_{4})_{2}+3\text{CaO}+3\text{H}_{2}\text{O}. \tag{3}\]  
The immersion test result showed rapid degradation behavior of MgO/Mg(OH)\({}_{2}\) NPs in DMEM due to the release of more OH\({}^{-}\), which was indicated by an increase in the pH values for the concentrations 10 mM, 50 mM, and 100 mM when compared to lower concentrations (1 mM and 5 mM) and the control groups. On the basis of the results of the pH values obtained from the immersion test, we optimized the higher concentration selection to 50 mM, as no significant difference was observed between the 50-mM and 100-mM concentrations. Therefore, selected concentrations of 1 mM, 5 mM, 10 mM, and 50 mM of MgO/Mg(OH)\({}_{2}\) NPs were used for further live/dead assays and SEM analyses to determine cytotoxicity and morphological changes, respectively. The live/dead assay results showed that upon exposure to lower concentrations (1 mM and 5 mM) of MgO/Mg(OH)\({}_{2}\) NPs in hFOB 1.19 cells, proliferation and adhesion with fewer dead cells was observed.