How Gel Can Prevent Orthopedic Implant Infections

Chris Newmarker

November 19, 2013

5 Min Read
How Gel Can Prevent Orthopedic Implant Infections

Preventing infections is a major cause of implant failure, and a focus for orthopedic device manufacturers. One of the most promising solutions involves hydrogels, the same type of material used to make soft contact lenses.

The Stevens Institute of Technology in Hoboken, NJ, is a pioneer in the area, with patented technology for a hydrogel coating for implants.

Here's how a Stevens-produced news release from late 2012 describes the use of the gel:

"When a device is immersed in a colloidal solution of the microgels, the implant, whose surface has been given a positive electric charge, attracts negatively charged microgels. Because of their negative charge, once on the device surface the microgels repel each other and create an evenly spaced patchwork. This patchwork is highly desirable because the space between microgels is about the size of a bacterial cell (1 micrometer; for reference, a human hair is about 75 micrometers thick), so the surface repels bacteria. Bone tissue cells are larger than bacterial cells and have fluid cell membranes that can conform to the surface. Data shows that bone cells will grow over the microgels and stick to exposed surface between the microgels."

Matthew Libera, a chemical engineering and material science professor at Stevens, also enabled the gel to release antimicrobial compounds to fight the bacteria.

"Usually the only way to resolve a biomaterials-associated infection is to remove the device, treat the infected tissue, and later implant a second device," Libera says.

"Not only does this bring really significant cost to the health-care system,  it forces the patient to undergo a lengthy and challenging surgical and rehabilitation process over a long period of time. We would like to eliminate that risk," Libera said in the Stevens news release.

This is serious business because of the devastating nature of orthopedic implant infections. Bacteria can produce antibiotic-resistant "biofilms" around the implants.

"Disease-carrying bacteria, viruses, and parasites that get into the body can destroy healthy tissue, multiply and spread through blood," says an American Academy of Orthopaedic Surgeons webpage about the subject.

Mayo Clinic estimates that the total number of hip arthroplasty and total knee arthroplasty implantations done in the U.S. each year will increase from approximately 600,000 to 4,000,000 by 2030 as the active but aging baby boom generation replaces is worn out joints. Assuming a 1% to 5% risk of infection from all prosthetic joints, Mayo expects the incidence of such infections to skyrocket at a similar pace.

Libera is part of a whole group of researchers across disciplines at Stevens who have been trying to crack the device-related infections problem.

Other hydrogel-related advances are taking place in Singapore, where the Institute of Bioengineering and Nanotechnology and IBM Research early this year unveiled an antimicrobial hydrogel able to break apart biofilms and destroy multidrug-resistant superbugs upon  contact. It is a discovery that could be used for medical devices, wound healing, contact lens coating, skin infection and dental fillings.

The new gel developed in Singapore is made up of what researchers described as a "novel polymer material jointly developed by IBN and IBM Research in 2010." The polymer forms into a moldable gel when mixed with water and heated to human body temperature, so the gel can be targeted at various parts of the body. It is also biodegradable, allowing for natural elimination from the body.

Meanwhile, Massachusetts Institute of Technology researchers have been working on how to layer antimicrobial agents on devices in nanostructured thin films in order to make the antimicrobial agents more effective.

"Many labs are actively studying systems for releasing combinations of antibiotics, antimicrobial peptides, and growth inducers. Drug release can be initiated by a trigger such as ultrasound or merely by their final form. One could envision that given the right combination of a hydrogel and a stronger weight-bearing system, composites could be created that will foster new bone growth in an infection-free environment," says Noreen Hickok, associate professor in the departments of orthopaedic surgery and biochemistry and molecular biology at Thomas Jefferson University in Philadelphia.

The gels, though, also have their issues, according to Hickok, who spoke with MPMN earlier this year.

"The reports that I have seen, however, indicate that hydrogels suffer from the same problems as many other controlled-release systems in that their ability to control infection is limited to the first several days to weeks after surgery. In the case of their prophylactic use during a primary surgery, this elution time would probably be sufficient, but I have grave doubts as to whether this timeframe would be sufficient in a revision surgery," Hickok says.

Hickok thinks silver applications are one of the hottest technologies presently for preventing infections on implants. "We would like to think that the antibiotic-bonded implants that we have developed at Thomas Jefferson University have real potential," Hickok says.

Chris Newmarker is senior editor of MPMN and Qmed. Follow him on Twitter at @newmarker and Google+

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