When someone receives an implant such as an artificial hip, there's a real risk of an infection occurring at the implant site. According to a new study, however, a covering of bacteria-frying gold nanorods could keep that from happening.
Bacterial infections at the sites of recently installed implants can be very serious, potentially leading to complications such as a weakening of the bond between the implant and the bone. When this happens, subsequent surgeries are often required in order to keep the implant from prematurely failing.
A number of research institutes are working on antibiotic coatings for implants – to get them past the initial infection-prone state – although some of those substances continuously release their antibiotic payload, regardless of the state of the site. This indiscriminate use of the drugs can cause bacteria to build up a resistance to them, thus making the antibiotics less effective.
That's where the gold nanorods come in.
Developed by scientists at Sweden's Chalmers University of Technology, the minuscule objects could be easily applied to the surface of implants, and have already been lab-tested on glass surfaces. The rods are quite widely spaced from one another once applied, covering a combined total of only about 11% of the underlying material.
As long as the nanorods aren't exposed to near-infrared light, they remain inert. When they are exposed to it, however, the electrons in their outer layer are set in motion. This reaction generates heat, which kills any microbes on the surface. In the case of an implant, the light could be applied externally, shining through the skin and tissue to reach the implant's surface.
Importantly, the heating effect is localized enough that it has very little effect on the surrounding tissue. That said, some tissue cells immediately adjacent to the rods may be destroyed. The scientists believe this shouldn't be a problem, though, as the small number of affected cells would be quickly regenerated by the body.
"The trick is to tailor the size of the rods," says Prof. Martin Andersson, who led the study along with doctoral student Maja Uusitalo. "If you make them a little smaller or a little bigger, they absorb light of the wrong wavelengths. We want the light that is absorbed to penetrate skin and tissue well."
It's additionally important to control the intensity of the near-infrared light, which corresponds to the amount of heat generated. If the temperature of a nanorod exceeds 120 ºC (248 ºF), the object will permanently transform into an orb that won't absorb the light.
It is hoped that once the technology is developed further it could be used to prevent infections in the weeks after surgery, via periodic applications of near-infrared light. The research is described in a paper that was recently published in the journal Nano Letters.
