Quantifying the relationship between biofilm reduction and thermal tissue damage on metal implants exposed to alternating magnetic fields.

ABSTRACT

AIM: Metal implant infections are a devastating problem due to the formation of biofilm which impairs the effectiveness of antibiotics and leads to surgical replacement as definitive treatment. Biofilm on metal implants can be reduced using heat generated by alternating magnetic fields (AMF). In this study, the relationship between implant surface biofilm reduction and surrounding tissue thermal damage during AMF exposure is investigated through numerical simulations. METHODS: Mathematical models of biofilm reduction with heat were created based on in vitro experiments. Simulations were performed to predict the spatial and temporal heating on the implant surface and surrounding tissue when exposed to AMF. RESULTS: The modeling results show that intermittent and slow heating can achieve biofilm reduction with a narrow zone of tissue damage around an implant of less than 3 mm. The results also emphasize that uniformity of implant heating is an extremely important factor impacting the effectiveness of biofilm reduction. For a knee implant, using a target temperature of 75 °C, an intermittent treatment strategy of 15 exposures (10 s to target temperature followed by cooldown) achieved a bacterial CFU reduction of 6-log10 across 25% of the implant surface with less than 3 mm of tissue damage. Alternatively, a single 60 s heating exposure to same temperature achieved a bacterial reduction of 6-log10 across 85% of the implant surface, but with 4 mm of tissue damage. CONCLUSION: Overall, this study demonstrates that with uniform heating to temperatures above 70 °C, an implant surface can be largely reduced of biofilm, with only a few mm of surrounding tissue damage.