Researchers at UT Southwestern claim that short exposure to high-frequency alternating magnetic fields (AMF) has the potential to destroy bacteria that ends up in biofilms growing on the surface of implants.
The researchers, Rajiv Chopra and David Greenburg, found that the magnetic fields heat the surface of metal prosthetic joints to destroy bacterial biofilms. If the direction of the magnetic fields is moved back and forth quickly, the electrical currents will only flow along the outer edge of the metal where the biofilm is found.
“That was the lightbulb in the conversation,” said Chopra, associate professor of radiology, in a press release. “You have a pathogen that can’t be treated with conventional drugs. You have a physical effect – heating on the surface of a metal – that’s often a complication for imaging technologies such as MRI. We’ve taken two things that are problems and, by putting them together, we’ve turned up a solution.”
Biofilm is a group of microorganisms that adhere to a surface and, over time, cause chronic infections and become resistant to antibiotics. The New England Journal of Medicine reports that biofilm infections are more likely to arise in people who have cystic fibrosis, diabetes and chronic obstructive pulmonary disease. About 648,000 people had a total of 721,800 healthcare-related infections in 2011.
Biofilm infections are one of the most serious complications that occur with hip and knee replacement surgeries, according to Greenburg.
“We were looking for better ways to target and treat biofilms. Our idea was to put a coil around the joint and run a current through it to create alternating magnetic fields,” Greenburg said. “Human tissue isn’t conductive but metal is, so only the implant would heat up.”
Electrical currents are delivered through a wire that creates a magnetic field. The magnetic field is concentrated in the center of the coil. The direction of the magnetic field depends on which way the electricity is flowing. If the electric current are more than 100 kHz, the metal surface of the prosthetics in the coil will begin to heat.
The researchers used a prosthetic joint model to demonstrate that applying heat to the metal surface through AMF could destroy biofilm and kill bacteria. They also tested the method on several different types of bacteria that are known to create biofilms on artificial joints and found that the magnetic fields worked on all of the species.
Antibiotic treatment effectiveness was also increased when receiving AMF.
“Think about heat as a drug for a minute,” Greenburg said. “Sometimes in infectious diseases we want to know whether two drugs are synergistic, meaning one plus one equals four, which is the case with AMF and antibiotics. That’s important because if treatments are synergistic, you can use lower concentrations of each, which has implications for safety as well as cost.”
The researchers also tested the AMF method in mouse models and found that high-power and short-duration doses of AMF minimized heat damage to surrounding tissues. The high power allows for it to reach a target temperature on the metal surface quickly before the heat can accumulate in surrounding tissues.
Currently, patients have to have biofilm-covered prosthetics removed and have a temporary spacer put in while receiving intravenous antibiotics over a six-week period. Then they have to go through a second knee replacement surgery.
“Periprosthetic joint infections are a devastating complication to patients and are a significant financial burden to our health care system,” said orthopaedic surgeon Kenneth Estrera, an assistant professor at UT Southwestern. “The research by Dr. Greenberg and Dr. Chopra may lead to a solution to the most challenging problem in joint arthroplasty surgery.”
This research was published in the journal Scientific Reports.