Researchers at Chalmers University of Technology in Sweden have developed a new method to sterilize medical implants using gold nanorods.
This technology uses tiny rods of gold heated with near-infrared (NIR) light to kill bacteria on the surface of implants, such as knee or hip replacements.
The findings, published in Nano Letters, could be a significant advancement in the fight against antibiotic resistance.
When foreign materials like implants are placed in the body, the risk of infection increases.
These infections are hard to treat because the body’s immune system is weakened by the presence of the implant.
As a result, patients often need long-term antibiotic treatments, which can contribute to the rise of antibiotic resistance—a growing global health threat, according to the World Health Organization (WHO).
To tackle this, the researchers at Chalmers developed a method that attaches gold nanorods, just a few nanometers in size, to the implant’s surface. When exposed to NIR light, these nanorods heat up like tiny frying pans, killing any bacteria present without harming surrounding tissues.
“The gold rods absorb the light, and the electrons inside them begin to move, generating heat. The bacteria are then ‘fried’ to death,” explained Maja Uusitalo, a doctoral student and lead author of the study.
NIR light is invisible to the human eye but can penetrate human tissue, allowing doctors to heat the nanorods on an implant even after it has been inserted into the body.
The gold rods cover only about 10% of the implant’s surface, preserving the implant’s essential properties, like its ability to bond with bone.
The key to this technology is getting the size of the nanorods just right. If they are too large or too small, they won’t absorb the correct wavelength of light needed to penetrate the skin and heat the rods effectively.
To understand how the gold nanorods affect bacteria and human cells, the researchers needed to measure the temperature of the rods precisely.
Regular thermometers are too large to measure something so tiny, so the team used X-rays to observe how the gold atoms move. This technique allowed them to monitor and control the temperature of the nanorods.
The rods need to stay below 120°C because higher temperatures can cause them to lose their shape and effectiveness. If the rods transform into spheres, they can no longer absorb NIR light properly, making them useless for sterilization.
One of the technology’s key benefits is that it only becomes active when NIR light is applied. This allows doctors to control when the implant surface should be antibacterial, avoiding negative effects on the healing process.
“We believe this technology could be used to heat the gold nanorods shortly after the implant is placed and the wound is closed, killing any bacteria that may have settled during surgery,” said Martin Andersson, the research leader at Chalmers.
While a few human cells might be damaged during the heating, Andersson noted that the body quickly replaces them, minimizing any impact on healing.
The Chalmers research team hopes to bring this technology into healthcare, helping to create safer implants and reduce the need for antibiotics in surgeries.
