**2.2. Ball-cratering wear test**

An instrument with free-ball configuration was used for the sliding wear tests. Two load cells were used in the ball-cratering apparatus: one load cell to control the normal force (N) and one load cell to measure the tangential force (T) developed during the experiments. "Normal" and "tangential" load cells had a maximum capacity of 50 N and an accuracy of 0.001 N. The values of "N" and "T" were registered by a readout system. **Table 2** presents the test conditions selected for the experiments conducted in this work. Balls for the ball-cratering wear test were made of AISI 316L stainless steel, with a diameter of D = 25.4 mm (D = 1″). A phosphate buffer solution (PBS), with chemical composition (g/l): 8.0 NaCl, 0.2 KCl, 1.15 Na2 HPO<sup>4</sup> , 0.2 KH2 PO<sup>4</sup> , with a pH value of 7.4 and a conductivity of 15.35 mS was dropped between the ball and the specimen.


**Table 1.** Frequencies used for ytterbium optical fiber laser treatment.

**Figure 2.** ISO 5832-1 austenitic stainless steel textured by ytterbium optical fiber laser.


**Table 2.** Test conditions selected for the ball-cratering wear experiments.

The values of normal force (N) were defined as a function of the density (*ρ*) of the ball material (AISI 316 L SS): *ρ*316L = 8 g ·cm−1.

The tests were conducted at t = 10 min. The sliding distance (S) was calculated based on the values of *v* = 0.1 m·s−1 and t = 10 min (t = 600 s) and was equal to 60 m.

All experiments were conducted without interruption, and the PBS solution was continuously agitated and fed between the ball and the specimen under a frequency of 1 drop/2 s. Both the normal force (N) and the tangential force (T) were monitored and registered constantly. Then, the friction coefficient (μ) was determined using Eq. 2:

$$
\mu = \frac{T}{N} \tag{2}
$$

**2.5. Roughness analysis**

**2.6. Cytotoxicity analysis**

number of viable cells on the plate.

**3. Results and discussion**

using the same test for a different tribological system.

**3.1. Wear volume analysis**

texturizations (blank).

A LEXT OLS 4100 confocal laser scanning microscope (Olympus, TM) was used in order to obtain the surface roughness of the laser-textured and untreated samples with a higher definition quality in the topographic analysis. The values are expressed as the mean roughness Ra.

Evaluation of the Biotribological Behavior and Cytotoxicity of Laser-Textured ISO 5832-1…

http://dx.doi.org/10.5772/intechopen.73140

69

Cytotoxicity was assessed by quantitative methodology. The test is based on the determination of viable cells after exposure of the cell population to the extract obtained from incubation of the samples in cell culture medium RPMI (Gibco®) supplemented with serum bovine fetal 10% and antibiotic/antimycotic (solution Gibco®) 1% at 37°C for 9 days under constant gentle stirring. The long period use was chosen to mimic if the samples were implanted. The treated surface was carefully immersed in cell culture medium to evaluate if there was debris released from the samples that can lead to a cytotoxicity effect. The extract of each sample were used to

cultivate on a cell monolayer, CHO (Chinese Hamster Ovarian) cell line for 24 hours.

The analysis of the number of viable cells was performed by the colorimetric method for the metabolization of *supravital* dye, MTS, and the electron coupling agent, PMS (Promega®) were used as the supplier instructions, and subsequently reading in a spectrophotometer at 490 nm. The amount of dye metabolized by the cell population is directly proportional to the

The environment of implants usually induces wear deriving from the contact between the biomaterial and surrounding tissues, so that when manufacturing an implant, one has to choose a suitable area for laser treatment. **Figure 3** shows this biomaterial surface without

**Figure 4** presents the wear volumes (V) for the untreated and laser-textured samples after the ball-cratering wear tests. These values were determined according to Eq. (1). It is possible to observe that the wear volume decreased for the laser-textured specimens with respect to the untreated steel. This fact is likely to be associated with an increase in the surface hardness after laser texturing. As shown in **Table 3**, the microhardness of the laser-textured samples was higher than that of the untreated material. The highest values of wear volume were obtained for the untreated specimens. The wear resistance of the laser-textured surfaces was superior to that of the pristine material. Similar results were reported by Cozza et al. [13]

Microstructural and topographic modifications due to changes in some parameters of the laser beam were identified by Lima et al. [24]. They used a Q-switched Nd: YAG laser with different pulse frequencies. Similarly, they performed texturing treatment that consisted of

#### **2.3. Nanotribometer**

The tribological behavior of the ISO 5832-1 austenitic stainless steel was also assessed by wear tests conducted in a nanotribometer (Anton Paar—model NTR2 ). The tests were performed in the air, at 25°C, with counterbody of chrome steel 52–100 rotating ball shape, 2 mm in diameter, during 10 min, with normal force of 100.0 mN, distance equivalent to 2.4 m, and a scan speed of 4.0 cm.s−1. Both laser-textured and pristine materials were evaluated.

#### **2.4. Microhardness (HV)**

Vickers microhardness analyses were performed in a microdurometer coupled with optical microscope, Fisherscope HM 2000. The hardness values refer to the average of five measurements at a distance of 50 μm between each indentation, and applied load of 25.0 mN·0−1, for surfaces treated with laser and also for the untreated stainless steel specimens.
