## 4 Magnesium Alloys for Biomedical Implants  
Achieving successful implant integration requires outstanding biocompatibility; thus, medical implants must meet stringent standards for materials, including being non-toxic, non-carcinogenic, non-symrogenic, non-allergic, non-inflammatory, and hemocomputable. In the laboratory, it is essential to simulate the physiological conditions when performing in vitro tests, including cytotoxicity assays and cell proliferation studies, to evaluate the potential material effects on the host organism and assess the biocompatibility of the biodegradable implants before implantation [37]. Magnesium (Mg) alloys, which are generally biodegradable, have garnered considerable attention in the biomedical field in recent years. In addition to mechanical characteristics such as human bone, Mg shows excellent biocompatibility. As mentioned above, Mg is a vital supplement for keeping the human body healthy and promoting osteo-growth [2; 51; 52]. Additionally, during corrosion in the biological environment, Mg\({}^{2+}\) is released, creating non-toxic magnesium hydroxide, hydroxyl ions, and hydrogen gas (as shown above), which are removed from the body via the kidneys [53; 54; 55; 56; 57]. On the other hand, the main disadvantages of using Mg alloys are the rapid degradation rates and decrease in mechanical properties, which may cause implant failure faster than the healing process [58]. Moreover, hydrogen gas emitted from corrosion may create gas pockets that cause the adjacent tissues to separate, and the OH\({}^{-}\) ions may cause surface alkalization and potential cell damage [59; 60]. Additionally, the mechanical properties of Mg could be \begin{table}
\begin{tabular}{l l l l} \hline \hline
**Magnesium Alloy** & & & \\
**with \% of Hyaluronic Acid (HA)** & & & \\ \hline \hline \multirow{3}{*}{Mg-6 Zn-5\%HA} & 15\% reduction in weight & \multirow{3}{*}{SBF, 30 days} & \multirow{3}{*}{Static} \\  & loss after 30 days of & & \\  & immersion time & & \\  & Enhanced degradation rate & & \\ Mg-3 Zn-5\%HA & by 40\% for the initial 14 & & \\  & days of immersion & & \\ Mg-5\%HA & Huge decrease in corrosion & & \\  & rate (around 75\%) & & \\  & & & \\ AZ91–20\%HA & Improved degradation rate & Artificial Sea Water, & \\  & & 24 and 72 h & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Corrosion rate of different Magnesium alloys [11]. improved by alloying. Thus, there are various challenges to tackle in developing Mg alloys. The advantages and disadvantages of Mg material are summarized in Tables 5 and 6. Even though Mg has many benefits as an implant material, pure Mg is not recommended for biomedical applications due to its higher corrosion rate and insufficient mechanical properties. Moreover, Mg shows low ductility because of the lack of slip characteristic in its hexagonal closest packed (hcp) structure. These problems are averted by alloying, which creates microstructural changes and adjusts surface potential between phases, improving mechanical properties and corrosion resistance [61, 62]. Common alloying elements for Mg are aluminum (Al) and zinc (Zn), as they contribute to hardness, strength, and castability. Lithium provides low density and high solid solubility to Mg alloys. Moreover, Li can change the formability of Mg alloys by changing the crystal structure of Mg from hcp to the body-centered cubic (BCC) [56]. Alloying elements refine grains and optimize the type, size, and distribution of the second phase, which reduces the corrosion rate of Mg alloys. Furthermore, alloying elements create passive films to impede further corrosion. Presently, aluminum (Al), zinc (Zn), manganese (Mn), calcium (Ca), strontium (Sr), zirconium (Zr), and neodymium (Nd) are commonly used as alloying elements.