In Vitro Corrosion Analysis in Low-Intensity, Pulsed Ultrasound

Clinical investigations have demonstrated a reduced time to union in certain fractures whose management is augmented with low-intensity ultrasound. It is
hypothesized that ultrasound augmentation is attributable to mechanical stimulations at the cellular level. Additionally, mechanical stimulation of various magnitudes affects the corrosion rate of metals. Therefore, the effect of ultrasound on the corrosion properties of orthopedic implant materials warrants evaluation
prior to recommending ultrasound as an adjunctive treatment for fractures in the presence of internal fixation devices.

The purpose of this study was to determine whether low-intensity ultrasound adversely affects the corrosion properties of 316L stainless steel, a commonly
used metal in surgical implants. An electrochemical cell was used to expose 316L stainless steel specimens to a corrosion environment. Experimental specimens
were subjected to low-intensity ultrasound at the clinically applied intensity. Polarization curves were used to extract average corrosion current density in the passive region, primary passive potentials, and transpassive potentials.

Analysis revealed no significant differences between the experimental and control corrosion current density, primary passive potentials, or transpassive potentials.
Based on this in vitro analysis, we demonstrated no significant difference in corrosion rate between controls and exposed samples. We conclude that low-intensity ultrasound has no adverse effect on the corrosion properties
of stainless steel implant materials.