*2.2. Material Properties*

Particular attention should be given to the physical and mechanical properties of the bone tissue. The pelvic bone consists mainly of low-density spongy tissue and a thin and dense cortical layer. Most of the load is transferred through the cortical layer, and the spongy tissue works as a support material, preventing the cortical layer from collapsing. Due to age and other reasons that may cause degradation of bone tissue, the mechanical properties can change [14–17]. Bone tissue is anisotropic [12,14,18,19], and the distribution of Young's modulus depends linearly on the density. However, the variation in Young's modulus both for the compact and spongy tissue is negligible for the pelvic bone, as proven previously [9,14]. Many papers devoted to the pelvis finite element study considered the pelvic bone as isotropic and linear elastic [1–8]. After analysing the data from these sources, the mechanical properties are summarised in Table 2.



It is important to mention that the yield strength reported previously [12–14] for spongy bone seems excessively high. From a clinical point of view [20], the spongy bone has a yield strength of approximately 1%, so some additional evaluation is required to confirm that the spongy bone could be loaded up to 2–3% of strain without any plastic deformation, damage, or fracture. Therefore, a value range of 1.4–2.1 MPa was used in this study as the ultimate strength of the spongy bone. Data reported previously [20] were confirmed by the authors' research on spongy tissues extracted from the femoral head after surgery [15].

The next important point is to study the material characteristics of the other parts of the assembly. The main advantages of titanium alloy Ti-6Al-4V are good corrosion resistance under all conditions and excellent biocompatibility.

The screws and prosthetic head should be made of normal solid titanium alloy Ti-6Al-4V [21], and the considered implant is manufactured by 3D printing [22]. The mechanical properties of 3D printed and solid titanium are slightly different, particularly those characterizing the fatigue behaviour [23].

Finally, the acetabular liner is made of ultrahigh-molecular-weight polyethylene [24]. This polyethylene, reinforced with chemical cross-links, is distinguished by its strength, low friction coefficient, and high biocompatibility. These properties allow using it for artificial joints.
