Integrity of Metallic Medical Implants in Physiological Solutions

Stainless steel and Ti alloys are increasingly used as biomaterials for implants and prosthesis because of their lower elasticity modulus and superior biocompatibility. In the present study different electrochemical measurements have been used to characterize the in vitro surface integrity of two surgical grade alloys: 316L stainless steel (SS) and Ti-6Al-4V alloy (TA). Both alloys are commonly used for orthopaedic and ostesynthesis implants. The aim was to compare their corrosion performance during soaking over an extended period of time in two physiological solutions; Ringer saline (RS) and phosphate buffer saline (PBS). The open circuit potential indicated that both samples exhibit spontaneous passivation. Electrochemical impedance spectroscopy (EIS) data revealed that the corrosion mechanism of both alloys can be modified according to the chemical composition of the test solution. Hence, RS was found to be more corrosive than PBS, especially for SS which possesses higher corrosion rate than TA. However, in PBS the passive traits of SS become comparable to those for TA due to PO4 3-contamination, as confirmed by SEM and EDX examinations