## 2 Mechanical Properties  
A critical requirement for any load-bearing implant material is aligning its mechanical characteristics with those of human bone. Whether composed of metal, ceramic, polymer, or their combinations, the material's mechanical performance must be tailored based on tissue characteristics and load requirements at the specific implantation site [23]. To this end, some very general and exemplary mechanical and durability prerequisites are summarized in Tables 1 and 2. The choice of materials for implants is often guided by their specific mechanical properties, tailored to their intended applications within the human body. For instance, Titanium-based alloys are commonly employed in bone fixation devices and high-load scenarios such as hip prosthetics, whereas cobalt-based alloys are preferred for joint replacement [25; 26]. An implant material must exhibit an adequate modulus and yield strength to fulfill its intended function. Furthermore, for implants such as hip and knee replacements, robust fatigue resistance under substantial loads is imperative [27]. The key mechanical properties essential for evaluating an implant include tensile modulus, yield strength, hardness, compressive and shear strength, toughness, fatigue strength, and permanent elongation [28]. These mechanical characteristics should closely match those of human bone to withstand decades of use and minimize the phenomenon of stress shielding. Furthermore, implant materials should exhibit outstanding wear resistance, especially for articulating surfaces such as hip and knee prostheses, often associated with surface hardness. Minimizing the formation and propagation of cracks is also vital in high-load applications [29]. [PERSON] et al. investigated the mechanical properties of biological Mg-Zn-Ca alloy for bone implants before and after high-pressure torsion (HPT) processing. HPT enhances microhardness and tensile strength but reduces toughness, while annealing at 210 \({}^{\circ}\)C for 30 min balances microhardness distribution and significantly improves plasticity. The Mg-Zn-Ca alloy exhibited optimal comprehensive mechanical properties after five turns of HPT, followed by annealing [30]. A novel strategy for achieving the optimal balance between the mechanical performance of alloys and meeting load-bearing requirements is by creating porous structures in implant materials. Powder bed fusion techniques, facilitated by lasers, contribute to the generation of low-density magnesium structures, thereby reducing the stress-shielding effect. The advantage of employing this technique over other manufacturing methods lies in the ability to adjust porosity levels compared with alternative additive manufacturing techniques. This technique produces magnesium with controlled porosity, which will exhibit a predetermined external form and internal structure that complements bone rigidity, eliminating the necessity for stress shields during manufacturing. Table 3 shows different mechanical properties of biodegradable and non-biodegradable alloys. \begin{table}
\begin{tabular}{c c} \hline \hline \multicolumn{3}{c}{**Mechanical Performance**} \\ \hline
**Biomaterial** & **Mechanical Characteristics** \\ \hline Hip prosthesis & Strong and rigid \\ Tendon material & Strong and flexible \\ Heart valve leaflet & Flexible and tough \\ Articular cartilage & Soft and elastomeric \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Examples of mechanical and durability requirements for general biomedical material design [24]. \begin{table}
\begin{tabular}{c c} \hline \hline \multicolumn{3}{c}{**Mechanical Performance**} \\ \hline
**Biomaterial** & **Durability** \\ \hline Bone plate & Six months or longer \\ Hip joint & Ten years or longer under heavy loads \\ Heart valve leaflet & Able to fully flex 60 times/min without \\  & undergoing failure for several decades \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Examples of durability conditions for biomedical implant design [24].