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Researchers at Chalmers University of Technology in Sweden have developed a new technology to enhance sterilization of surgical implants, especially hip and knee replacements. The technique leverages near-infrared (NIR) light to heat minuscule gold nanorods attached to implant surfaces, creating a localized sterilizing effect without harming surrounding tissue. This sterilization method offers a targeted solution to reduce antibiotic dependence and associated resistance – a major global health issue highlighted by the World Health Organization (WHO).
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Addressing implant-associated infections with targeted heating
Implant surgeries, particularly those involving materials like titanium or specialized plastics, carry a heightened risk of infection. As these materials can suppress immune responses, antibiotics are often used for prevention or treatment, sometimes leading to long-term antibiotic courses. The technology from Chalmers introduces a different approach by attaching nanoscale gold rods directly onto the implant. When exposed to NIR light, these rods heat up, targeting only bacteria on the implant’s surface. This prevents heat from affecting the surrounding tissue and minimizes the risk of damaging healthy cells.
“The gold rods absorb the light, the electrons in the gold are set in motion, and finally the nanorods emit heat. You could say that the gold nanorods work like small frying pans that fry the bacteria to death”
Maja Uusitalo
Gold nanorods as localized heating elements
The nanorods absorb NIR light and heat up, functioning as tiny heating elements. Because they are so small, they produce highly localized heat, which sterilizes the implant surface without affecting nearby tissue. NIR light itself has the unique ability to penetrate human tissue, which means that once an implant is placed, the surface can be sterilized externally. The gold rods only cover about ten percent of the implant surface, leaving the structural integrity and bone attachment properties of the implant intact.
Near-infrared (NIR) light
NIR light is part of the infrared spectrum and is invisible to the human eye. With wavelengths longer than visible light, it can penetrate body tissue to a degree, making it useful in medical treatments that require light delivery through skin layers.
Antibiotic resistance
This occurs when bacteria evolve to withstand the effects of antibiotics, making infections harder to treat. It is a significant concern for global health, as resistant infections can lead to prolonged illness, higher medical costs, and increased mortality.
Nanorods
Nanorods are rod-shaped nanoscale particles, often made from metals like gold. Their small size and specific shapes allow them to interact with light and heat in ways that can be highly localized, which is useful in medical applications like targeted heating for sterilization.
X-ray temperature measurement
This technique involves using X-rays to monitor atomic movement in materials. Since temperature affects atomic motion, X-ray analysis provides an indirect method for measuring the temperature of tiny objects like nanorods, which are too small for traditional thermometers.
Measuring and managing nanorod temperature
Precise control over the nanorods’ temperature is crucial for effective sterilization. If the temperature of these nanorods exceeds 120 degrees Celsius, they lose shape, transforming into spheres and losing their ability to absorb NIR light effectively. To ensure temperature accuracy, the researchers used X-rays to analyze the movement of gold atoms within the nanorods, which provides an indirect temperature measurement. This method allows for control over heating intensity to avoid damage to the surrounding tissue.
Controlling bacterial sterilization with NIR light
The new technology offers flexibility in bacterial sterilization timing. The nanorods are inert until activated by NIR light, which allows for selective activation. This activation can take place shortly after implantation to eliminate bacteria that might settle during surgery, with the ability to turn the sterilization “on” and “off” as needed. Notably, this on-demand antibacterial property minimizes the common healing delays linked to conventional antibacterial coatings.
“We can control when the surface should be antibacterial and when it should not. When we turn off the light, the surface is no longer antibacterial and reverts to its original state. This is an advantage because many antibacterial surfaces usually have negative effects on healing.”
Martin Andersson
Expanding applications beyond implants
While this NIR technology has previously been explored in cancer treatments, Chalmers’ team is the first to apply it to implant sterilization. Early results are promising, with the technique’s precision and non-invasive sterilization approach presenting new possibilities for wider applications across various implant materials.
Reference: Uusitalo M, Strach M, Eriksson G, et al. Photothermal properties of solid-supported gold nanorods. Nano Lett. 2024;24(40):12529-12535. doi: 10.1021/acs.nanolett.4c03472
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