Remote Induction Heating of Metal Implants for Noninvasive Elimination of Pseudomonas aeruginosa Biofilm, Augmented by Tobramycin

Thermal shock is a promising new approach to eliminating biofilm infections on medical implants without surgically replacing the device. Most studies determining the minimum necessary thermal shock used immersion in hot media to provide precise, rapid, uniform temperature control. In vivo, however, this shock must be focused directly on the implant surface, raising the concern that bacteria may partially evade the shock by momentarily dispersing into the cooler surroundings. This study tests that hypothesis using remote induction heating, in which Pseudomonas aeruginosa biofilms were thermally shocked by an external alternating magnetic field heating the substrate directly. It also assessed the impact of tobramycin on the minimum thermal shock required. Susceptibility to tobramycin alone, thermal shock alone, and their combination was characterized over temperatures ranging from 50 to 80°C and duration of 1 to 30 min with biofilms of two distinctly different architectures and population densities. Remote heating was then evaluated on biofilms in a flow cell where media was continuously replaced to keep its temperature below the biofilm’s. Comparison with immersion heating showed that, despite losing 90% of the biofilm to dispersion into the flushed media, biofilms thermally shocked in the flow cell had significantly higher populations than biofilms comparably shocked by immersion, though biofilms could still be completely eliminated via remote heating. Tobramycin alone did not eliminate biofilm even at clinically infeasible concentrations but, when combined with thermal shock, achieved complete elimination at milder thermal shocks, indicating a complex synergy also observed with antibiotics of another class. Remote heating successfully eliminated biofilms while delivering heat in a clinically implementable manner. As an in vitro, these findings did not directly assess thermal damage to surrounding tissue, which requires further investigation in future treatment design.