Effects of Mechanical Stress on Corrosion Resistance of Metallic Biomaterials

Metallic biomaterials are commonly used as bone fixation devices in the field of orthopedics. They are usually used under a complex stress field in vivo. For example, they are statically stressed by the weight of the patient, and dynamically by exercise of the patient. Furthermore, in some cases, they are plastically strained and adjusted to the shape of the affected part. These stresses may degrade mechanical strength of the implanted metals. Implanted metallic biomaterials tend to corrode over time. Corrosion of implanted metals is harmful because it also causes strength degradation. Moreover, released metallic ions may be toxic to humans. In this study, in order to clarify the influence of the stress and pre-strain (10% and 20%) and their combination effect on corrosion behavior of AISI 316L stainless steel and Ti-6Al-4V alloy in vitro, a new testing system was developed. The system can apply load on a specimen in corrosion fluid. An electrochemical process was used to accelerate corrosion and to measure corrosion damage quantitatively. Anode polarization test were carried out in Ringer's solution. Corrosion resistance was assessed by measuring electric charge densities. After the test, the specimens were observed with a digital microscope and scanning electron microscope. Significant effects of stress and pre-strain on corrosion behavior were observed.