**1. Introduction**

Implantable medical devices used in mobile joints of the human body as well as for dental purposes require biocompatibility with the surrounding tissues and organs, mechanical strength, and corrosion resistance. The body fluids constitute a hostile environment for the implant, which is also subjected to various loads. The implant can release particles due to corrosion, corrosion associated with fatigue, and even friction against implantable components, bones, or other body parts. By coming into contact with the body fluids, these particles can be placed in locations far from the removed source causing complications to the patients.

Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons

Okasaki [1] evaluated the properties of metallic biomaterials with regard to the effect of friction on anodic polarization. He observed that corrosion was accelerated in the frictional environment with respect to static conditions. This effect was due to the formation of anodic areas in the stressed regions under friction whereas its periphery is cathodic.

electrolyte is supplied between the ball and the specimen during the experiments. The aim of the ball-cratering wear test is to generate "wear craters" on the specimen surfaces. The wear volume (V) may be determined as a function of *b*, using Eq. (1) [12], where *b* is the wear crater

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

Wear tests conducted under the ball-cratering technique present advantages in relation to other types of tests, because it can be performed with normal forces (N) and rotations of the sphere (n) relatively low (N < 0.5 N and n < 80 rpm) [17–21]. Tests in micro- and nanotribometers are used to investigate small regions and thin layers of different surfaces [22, 23].

The aim of this work was to evaluate the cytotoxicity and the tribological behavior of ISO 5832-1 austenitic stainless steel (SS) textured by Yb optical fiber laser, varying its pulse fre-

The material employed in the present work was a round bar (15 mm diameter) of the ISO 5832-1 austenitic stainless steel (chemical composition in wt%: 0.023 C, 0.78 Si, 2.09 Mn, 0.026 P, 0.0003 S, 18.32 Cr, 2.59 Mo, 14.33 Ni, and Fe balance). Specimens were treated with a nanosecond ytterbium (Yb) optical fiber laser at four different pulse frequencies, as shown in **Table 1**. A pulsed Nd: YAG laser (TRUMARK 5050™) was operated at a wavelength of 1062 ± 3 nm, with a laser average power of 50 W and a scanning speed of 200 mm s−1. **Figure 2** shows

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

value of 7.4 and a conductivity of 15.35 mS was dropped between the ball and the specimen.

**Specimens 1 2 3 4** Frequencies (kHz) 80 188 296 350

<sup>64</sup>*<sup>R</sup>* for *b* < < *R* (1)

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

67

HPO<sup>4</sup>

, 0.2 KH2

PO<sup>4</sup>

, with a pH

diameter and *R* is the ball radius.

**2. Experimental**

*V* ≅ *<sup>π</sup>b*<sup>4</sup> \_\_\_\_

quency, using two ball-cratering wear methods.

the surface finish of the laser-textured specimens.

(PBS), with chemical composition (g/l): 8.0 NaCl, 0.2 KCl, 1.15 Na2

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

**2.1. Material and sample preparation**

**2.2. Ball-cratering wear test**

Metallic particles released from the corrosion process may move passively, through tissue and/or circulatory system or can be transported in an active way when metabolized by macrophages [2]. In either case, this mass transport may lead to debris accumulation in surrounding tissues or even remote sites where they can participate in undesirable biological reactions, compromising biomaterial's biocompatibility.

Interaction between metallic implants and the human body can be affected by numerous factors such as the structure of the metal surface, its mechanical properties, size, and shape. When in contact with the body tissues after implantation, metallic devices affect the intensity of stresses to which the whole human body is subjected as well the implant itself. Wear and corrosion processes are additional effects arising from the interaction between metallic biomaterials and the body tissues [3].

The orthopaedic implants are projected and manufactured so that when used under the conditions and for the purposes designed, without compromising the clinical condition or the safety of patients. Any risks that may be associated with the implants use are acceptable when compared to benefits for the patients [2, 3].

The alloy described in part 1 of ISO 5832 [4] (ASTM F138/ASTM F139) is an austenitic stainless steel. It is one of the metallic materials most used in Brazil for manufacturing implants, because of its suitable mechanical strength, reasonable corrosion resistance, and low cost [5–8]. Stainless steel implantable medical devices are used as permanent or temporary implants to help bone healing. The laser texturing process is used to modify the biomaterial surface roughness and hardness.

The microscale abrasion test (or ball-cratering wear test) is a practical method to analyze the wear resistance of materials [8–11]. The ball-cratering wear test has gained large acceptance at universities and research centers and is widely used in studies focusing on the abrasive wear behavior of different materials [12–16]. **Figure 1** presents a schematic diagram of the principle of this wear test, where a rotating ball is forced against the specimen being tested and an

**Figure 1.** Schematic representation of the operating principle of ball-cratering wear test.

electrolyte is supplied between the ball and the specimen during the experiments. The aim of the ball-cratering wear test is to generate "wear craters" on the specimen surfaces. The wear volume (V) may be determined as a function of *b*, using Eq. (1) [12], where *b* is the wear crater diameter and *R* is the ball radius.

$$V \not\equiv \frac{\pi b^4}{64R} \text{ for } b \le \le R \tag{1}$$

Wear tests conducted under the ball-cratering technique present advantages in relation to other types of tests, because it can be performed with normal forces (N) and rotations of the sphere (n) relatively low (N < 0.5 N and n < 80 rpm) [17–21]. Tests in micro- and nanotribometers are used to investigate small regions and thin layers of different surfaces [22, 23].

The aim of this work was to evaluate the cytotoxicity and the tribological behavior of ISO 5832-1 austenitic stainless steel (SS) textured by Yb optical fiber laser, varying its pulse frequency, using two ball-cratering wear methods.
