Antibacterial coatings on hip and knee implants cut infection rates

Dec 13 2005

Putting antibacterial coatings on hip and knee implants and biomedical devices such as catheters could cut infection rates following surgery and significantly reduce health care costs and improve quality of life for patients, researchers at the University of South Australia have found.

A significant number of hip and knee implants are prone to infection after surgery and in many cases are not amenable to treatment with antibiotics, according to Hans Griesser, Professor of Surface Science and Deputy Director of UniSA's Ian Wark Research Institute.

"For patients in this situation it may be necessary to remove the implant from the infected site, cleanse the wound and undergo replacement surgery within a short time after original implantation, causing significant trauma, especially for the elderly," Professor Griesser said.

Catheters can also be a source of bacterial infections, which can spread from the skin to the incision for catheter insertion, and have been known to cause anaphylactic shock resulting in death, according to Professor Griesser. Hospitals combat this problem by removing and replacing catheters at frequent intervals, and at considerable cost to the health care system.

"Another significant problem caused by bacterial contamination of medical devices is bacteria that settle on contact lenses and cause inflammation and, more rarely, infections," Professor Griesser said.

Researchers at The Wark are developing nanometre thin coatings for biomedical implants and biomedical devices that prevent bacterial colonisation of implants that result in septic inflammation problems.

"We are using molecules called furanones, which are derived from natural chemicals originally extracted from Australian macro algae seaweed that grows off the eastern coast. The chemicals produced by these macro algae were found to prevent the colonisation of microbial organisms such as bacteria and fungi on their surfaces, helping to keep the algae clean. Researchers at the University of New South Wales developed synthetic analogues of the natural compounds and discovered that these chemicals also keep synthetic surfaces clean when placed on those surfaces in a marine environment. This provided the impetus for studying their use in biomedical device applications," Professor Griesser said.

Furanones have a unique advantage in that they act differently to other antibiotics. Unlike antibiotics, they don't kill bacteria. This means that the furanone compounds should not cause bacterial resistance, according to microbiologists.

"When bacteria sit on the surface, they first anchor themselves individually and then send out signalling molecules called homoserine lactones to other bacteria, which do the same, talking to each other via these signalling molecules until they reach sufficient density as a group on the surface. The bacteria then change their metabolism and start producing a slimy biofilm that protects them from antibiotics. Sitting under the protective biofilm, the bacteria multiply and grow, and that's what causes infection," Professor Griesser said.

Professor Griesser likens this process, called quorum sensing, to the example of soccer hooligans who on their own are quite ineffective but when they group together, can be a powerful force that creates havoc of disastrous proportions.

It's the furanones that come to the rescue by irreversibly switching off the bacterial signalling mechanism. Without the signal, the bacteria think that they are alone; they don't start producing the biofilm and eventually die on the surface.

"We attach the furanones by covalent bonding to our biomedical devices. We stress covalent bonding because it is important that we anchor them very firmly to the surface, making it impossible for them to break away and travel into remote organs such as the brain or liver," Professor Griesser said.

UniSA PhD student in applied science (minerals and materials), Sameer Al-Bataineh, has developed a fundamental understanding of the antibacterial coatings and how to make them. Using model substrates made from metal and plastics, he developed methods for attaching the furanones, and analysing their surface properties and chemical composition to get a detailed understanding of how they are best applied.

Al-Bataineh's research has been supervised principally by Professor Griesser and co-supervisor Dr Leanne Britcher at The Wark, with co-supervision by microbiologist Professor Mark Willcox from the Vision Cooperative Research Centre at the University of New South Wales, where he and Dr Hua Zhu assessed the antimicrobial efficiency of the coatings.

"The result is a good understanding of how the coatings work and in which way we can make them work for best effect. We have established recipes for practical applications of the furanone coatings onto different devices. We now have a very good basis for tailoring these coatings towards particular biomedical devices and are using this knowledge to work with Sydney-based company, Biosignal Limited, to develop antibacterial contact lenses," Professor Griesser said.

"This is an excellent example of where we can apply fundamental knowledge gained in a PhD towards commercial applications that we believe will have health benefits for a significant number of people. If we can apply this to biomedical implants and other biomedical devices, we will have a major impact on the health of the nation and the cost benefits will be enormous."