Shedding light on implant-associated infection

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Science Translational Medicine  25 Sep 2019:
Vol. 11, Issue 511, eaaz3709
DOI: 10.1126/scitranslmed.aaz3709


A coating on titanium-based orthopedic implants can be remotely activated using near-infrared light to kill bacteria growing on the implant surface.

Despite advances in minimally invasive surgery and aseptic techniques, infection remains an all too common complication after medical device implantation. Systemically administered antibiotics are largely ineffective for peri-implant infections due to bacterial drug resistance, poor drug penetration, and suboptimal bioavailability at the site of infection. If the infection takes hold, the implant will typically have to be removed, the infected tissue resected, and surrounding tissue lavaged with antibacterial agents prior to surgical revision. Antibacterial coatings can help reduce the likelihood of biofilm formation, but they are often only temporarily effective. Smart coatings, which either intrinsically recognize and disrupt biofilm formation on an implant surface or are remotely activated to achieve this function on-demand, would offer enormous benefit in reducing implant-associated infections.

Yuan and colleagues developed an antibacterial coating for titanium-based orthopedic implants that is remotely triggered by non-invasive, near-infrared (NIR) light. When NIR light is shone through soft tissue onto the underlying implant surface, the coating, comprised of mesoporous polydopamine nanoparticles, is activated in two ways to maximize biofilm disruption. First, the polydopamine component of the coating heats locally to about 50°C, a target temperature that is deemed likely to help kill bacterial cells without damaging the surrounding tissue. Second, the inclusion of a photosensitizer in the coating facilitates the release of reactive oxygen species, intended to disrupt bacterial cell membranes.

To test the coating’s translational potential, the researchers cultured titanium rods, with or without the coating, alongside Staphylococcus aureus, gram-positive bacteria that is commonly the cause of hospital-acquired infections. The rods were inserted in the femur in a rodent model and NIR light was shone on the implant sites for 10 min one day after surgery. Through explant and histological analysis, the team showed that the light-activated coating was up to 95% effective in disrupting S. aureus biofilm formation 4 weeks after implantation. Crucially, by tracking osteointegration the study showed promising signs of functional bone formation up to the implant surface.

Critical next steps must determine the longer-term biocompatibility and integrity of the coating, effectiveness in treating a range of bacteria, and whether NIR light activation can scale to be of clinical utility in scenarios where overlying soft tissue will be much thicker and the geometry of the implants more complex. However, this approach offers a leading light in the fight against implant-associated infection.

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