Effects of Electrically Activated Silver–Titanium Implant System Design Parameters on Time-Kill Curves Against Staphylococcus aureus

Abstract

Implant-associated infections pose serious threats to patients in terms of morbidity, mortality, and medical costs. This paper focuses on the quantitative assessment of the antimicrobial efficacy of a silver-based prophylactic system for orthopaedic implant applications. The implant system is configured to induce controlled local administration of silver ions via low intensity direct current activation (1–14 µA). We developed a broth-based in vitro testing model to evaluate the effects of important design parameters on the antimicrobial efficacy of the system over a 48-h interval. The time-kill curves obtained with various parameter levels were analyzed through a longitudinal model. Five parameters were investigated independently through one-way factorial experiments (n = 12) against Staphylococcus aureus. In phase 1 of the study, we investigated the effect of cathode material on system performance. We also determined the linear structure of the longitudinal model based on the Akaike information criterion by fitting the empirical data to multiple candidate model structures. The results show that substituting the silver cathode with titanium does not weaken the antimicrobial efficacy of the system (p = 0.9946). In phase 2, a detailed analysis with four design parameters was conducted using the silver–titanium configuration. The performance of the system was found to be independent of the electrode separation distance (p = 0.9926) and the pulsating current frequency (p = 0.9956). However, the anode surface area (p < 0.0001) and the current intensity (p < 0.0001) influenced the antimicrobial efficacy in an interactive manner. Overall, this study characterizes the in vitro antimicrobial efficacy of the proposed system and provides a reference of design parameters for future product engineering.