(358b) Wireless, Thermal Deactivation of Medical Device Infections Using an Iron Oxide Nanoparticle / Polymer Coating

Approximately 150,000 patients annually in the U.S. suffer from bacterial infections associated with implanted medical devices.  The biofilms formed in these infections are notoriously difficult to treat, and despite decades of research on non-fouling surfaces and antimicrobial agents, most of these infected devices must be surgically explanted and replaced. Our work investigates an alternative treatment strategy using heat to thermally deactivate these infections in situ without the need for additional surgeries. Remote heating can be achieved using an iron oxide (magnetite) nanoparticle / polymer coating exposed to an alternating magnetic field (AMF) (i.e. magnetic induction heating). This application applies heat at a precise location, requiring a much larger power density than previous magnetic hyperthermia applications that have been investigated for decades in suspension form. In this work, we demonstrate the effects of several design parameters on the overall heating of magnetite coatings, specifically, iron concentration, coating thickness, the type of immobilizing polymer matrix, coating swelling, and orientation of the coating relative to the exposed AMF. Magnetite nanoparticles were immobilized in two, FDA-approved polymer matrices: (poly(styrene) (PS) and poly(vinyl alcohol) (PVA)). Although the power output of these films scaled proportionally with increasing iron loading, other parameters indicate the design of a coating to achieve uniform heating is much less straightforward. Characterization of magnetite-polymer films revealed heating depends primarily on the polymer matrix and orientation of the film relative to the applied AMF. Heating rates were observed up to 717 W/g Fe for hydrated PVA films positioned parallel to magnetic field lines versus only 100 W/g Fe for non-hydrated PVA films positioned perpendicular to the applied AMF. In addition, a separate, in vitro thermal model was built to quantify the power density that may be needed for bacterial deactivation on a surface inside the body. The maximum power density measured from all polymer, orientation, iron concentration, and coating thickness combinations was 7.5 W/cm² which exceeded the peak power requirement (4.5 W/cm²) needed to achieve an 80°C surface temperature in 15 s beneath a tissue mimic heat sink. This work aims to eliminate a major liability of implanted medical devices and the billions of dollars spent on explantation, recovery, and re-implantation.