Abstract: BACKGROUND: Biofilm formation during the infection of orthopedic fixation devices is a very difficult clinical problem. Hypochlorous acid, as a highly effective disinfectant, can destroy the bacterial biofilm, which may be helpful for treating infection of orthopedic fixation devices.  
OBJECTIVE: To study the scavenging effect of hypochlorous acid on bacterial biofilm on the surface of orthopedic fixation devices after soaking and perfusion for different time in vitro.
METHODS: Staphylococcus aureus and Pseudomonas aeruginosa were colonized on orthopedic steel fixation devices for 3 days, and then the bacterial biofilm formed, which was confirmed by scanning electron microscope. Orthopedic fixation devices with two kinds of bacterial biofilms were soaked in hypochlorous acid for 0, 5, 10, and 20 minutes, or perfused with 6 L of a mixed solution of hypochlorous acid and saline (every 3 L of saline with addition of 120 mL of hypochlorous acid) for 20 minutes. The morphology of bacterial biofilms was observed under scanning electron microscope, and the scavenging effect on the bacterial biofilm on the surface of orthopedic internal fixation devices was then evaluated.  
RESULTS AND CONCLUSION: Pseudomonas aeruginosa: Under the scanning electron microscope, the bacterial biofilm plaques on the surface of the internal fixation device that was not soaked in hypochlorous acid solution were large and thick, and the colonies were densely concentrated. After 5, 10, and 20 minutes soaking in hypochlorous acid, the bacterial biofilm plaque area was gradually decreased and became thinner. Perfusion with 6 L of a mixture of hypochlorous acid and saline for 20 minutes could remove the bacterial biofilm. Staphylococcus aureus: The performance under the scanning electron microscope was consistent with the biofilm of Pseudomonas aeruginosa. To conclude, prolonging the soaking time or a mixed perfusion can enhance the scavenging effect of hypochlorous acid on the bacterial biofilm on the surface of internal fixation devices. By soaking in hypochlorous acid for a sufficient time, the bacterial biofilm colonized on the surface of orthopedic internal fixation devices can be degraded and destroyed, thus achieving the purpose of disinfection.

Key words: hypochlorous acid, bacterial biofilm, orthopedic surgery, orthopedic internal fixation device, infection, disinfectant