Effects of cathode design parameters on in vitro antimicrobial efficacy of electrically-activated silver-based iontophoretic system

Zhuo Tan, Anirudh Ganapathy, Paul E. Orndorff, Rohan A. Shirwaiker

Post-operative infection is a major risk associated with implantable devices. Prior studies have demonstrated the effectiveness of ionic silver as an alternative to antibiotic-based infection prophylaxis and treatment. The focus of this study is on an electrically activated implant system engineered for active release of antimicrobial silver ions. The objective was to evaluate the effects of the cathode design, especially the cathode material, on the in vitro antimicrobial efficacy of the system. A modified Kirby-Bauer diffusion technique was used for the antimicrobial efficacy evaluations (24 h testing interval). In phase-1 of the study, a three-way ANOVA (n = 6, α = 0.05) was performed to determine the effects of cathode material (silver, titanium, and stainless steel), cathode surface area and electrode separation distance on the efficacy of the system against Staphylococcus aureus. The results show that within the design space tested, none of these parameters had a statistically significant effect on the antimicrobiality of the system (P > 0.15). Subsequently, one-way ANOVA (n = 6, α = 0.05) was conducted in phase-2 to validate the inference regarding the non-significance of the cathode material to the system efficacy using a broader spectrum of pathogens (methicillin-resistant S. aureus, Escherichia coli, Streptococcus agalactiae and Aspergillus flavus) responsible for osteomyelitis. The results confirmed the lack of statistical difference between efficacies of the three cathode material configurations against all pathogens tested (P > 0.58). Overall, the results demonstrate the ability to alter the cathode material and related design parameters in order to minimize the silver usage in the system without adversely affecting its antimicrobial efficacy.