## 1 Introduction  
Total hip replacement (THR) is a successful procedure with relatively low complications [1; 2]. With the improvement of fixation and implant designs, and the introduction of minimally invasive techniques, the goal of THR is to minimize wear and osteolysis significantly reducing loosening of the components. Metal-on-metal (MOM) and ceramic-on-ceramic (COC) bearings are the most suitable solutions, especially for younger patients [3]. Metal-on-metal hip implants, introduced by [PERSON] and [PERSON] [4], were abandoned because of high frictional torques, inadequate surface finish, and high clinical failure rates, which resulted in extremely poor clinical outcomes. The second generation of MOM hip articulations, introduced by [PERSON] in 1984 [5], presented substantial improvements in terms of periprosthetic load distribution, range of motion (ROM, through the insertion of larger-diameter femoral heads) and a reduced dislocation risk [6]. Ceramic materials, introduced in hip arthroplasty more than 20 years ago, have been progressively attracted interest in the orthopedic field for they excellent biocompatibility, low coefficient of friction, and high wear resistance [7,8]. Moreover, they have good mechanical resistance [9] and produce lower wear rates than other combinations (i.e., metal-on-polyethylene and ceramic-on-polyethylene) [10, 11, 12, 13]. However, the principal limitations of COC prosthesis is dislocation (with small-sized heads) and head fracture risk [6]. [PERSON] and coworkers [14] observed the occurrence of stripe wear in first-generation alumina ceramic bearings. In particular, the stripes were shallower and the ball surfaces had higher compressive stress due to severe impingement and microseparation phenomenon. [PERSON] et al. [15] analyzed explanted prostheses from a single surgeon's 16 year series of Mittelmeier cementless total hip replacements and found that the majority of the explants exhibited stripe wear conditions with linear penetrations less than 0.15 mm and worn area surface roughness (Ra) of approximately 0.2 \(\upmu\)m.  
It is well known that composition, electric charge, wettability, and roughness of implant surfaces have great influence on their interaction with the biological fluids and tissues [16]. The importance of surface wettability has been highlighted in the scientific literature [17]. Wetting is the ability of a liquid to maintain contact with a solid surface, resulting from intermolecular interactions when the two are brought together. The degree of wettability (\(\theta\) angle) is determined by a force balance between adhesive and cohesive forces. The liquid drop contact angle is the angle that forms where the liquid-vapor interface meets the liquid-solid one and it is the main parameter used in the description of this phenomenon. Based on the value of the latter, which can be between 0 and 180\({}^{\circ}\), it is possible to affirm that \(\theta=0\) means a perfectly wetting surface; \(0<\theta<90^{\circ}\) means surfaces with high wettability; \(90^{\circ}\leq\theta<180^{\circ}\) means surfaces with low wettability. Ceramic materials offer a harder and more hydrophilic surface than metal alloys and can be polished to a lower roughness [18]. Some authors showed that, in hip wear simulator studies, femoral heads induced less Polyethylene wear compared with Cobalt-Chrome (CoCr) alloys [19, 20, 21]  
Evaluation of worn retrievals' ceramic articular surfaces is one method for verifying that damage patterns generated by hip joint wear simulation are comparable to those evident on explanted prostheses due to physiologic hip function. Unfortunately, partial and limited reports are available in literature due to the scarce number of available specimens and different types of ceramic used [10, 11, 20, 21]. Friction and wear processes are known to be affected by the surface wettability of the prosthetic materials [22, 23, 24], but definite correlations between wettability and tribological behavior are still to be established [17].