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Last Updated: Monday, 19 September 2005, 22:59 GMT 23:59 UK
Hi-tech coating to boost implants
Knee implants
Coating stops allergic reaction to knee implants
A coating for medical implants could help cut the risk of rejection and infections like MRSA, say scientists.

The chemically-inert diamond-like carbon (DLC) material can be used to coat plastics, metals and other natural materials used in implants.

Knee implants with a DLC coating have been successfully fitted to two arthritic patients allergic to the metal components underneath.

The Brunel University work featured at an Institute of Physics conference.

The coating makes implants more hard-wearing, and reduces friction between their components.

The coating is important because it prevents colonization of the tissue by bacteria, such as the superbug MRSA
Professor Joe Franks

It is also biocompatible, so unlike other types of coating it does not trigger the coagulation of blood.

And it can be deposited on a surface without having to heat the component to several hundred degrees, which means it is suitable not only for metals and ceramics, but plastics too.

Researcher Professor Joe Franks said: "We have developed coatings that can be used for catheters and various medical implants that go through the skin.

"The coating is important because it prevents colonization of the tissue by bacteria, such as the superbug MRSA."

Professor Gordon Blunn, of the Centre for Biomedical Engineering at University College London, was involved in fitting the knee implants.

He said both patients were allergic to the chromium which is contained in the most durable and long-lasting knee implants.

The only alternative would have been to have fitted less hard-wearing implants that could easily have worn out.

"By using DLC we were able to seal off the metal from the surrounding body fluids to create a very, very hard surface which did not cause problems with allergic reactions," he told the BBC News website.

Bypass operations

The Brunel team is working on a version of the coating to be used in combination with a natural body protein called collagen.

This combination could potentially be ideal for creating artificial arteries for use in bypass operations.

Lining collagen with DLC would enable blood to flow along the artery without risk of clotting.

The same pairing could also be used as a patch graft in repair operations, for instance to plug a hole left by the removal of a tumour.

Collagen is porous, which can cause the repair to be degraded by the acidic or alkaline chemistry of the body.

A DLC coating would solve the problem by forming a strong inert chemical barrier around the tissue.

Easier production

DLC was first produced in 1971 in a vacuum chamber using a technical and costly method that involved spraying charged carbon atoms at the surface to be coated.

Professor Franks' team has developed a more effective method known as plasma-assisted chemical vapour deposition (PACVD).

The component to be coated is mounted in a vacuum chamber on an electrode connected to a high-energy radio wave transmitter.

A hydrocarbon gas, such as methane or natural gas, is pumped into the chamber and the radio waves tear apart the hydrocarbon molecules and strip off the electrons from its carbon atoms to produce positive carbon ions.

These are attracted to the negatively charged component to produce the coating.

Professor Franks said: "The advantage of this method is that the ionized plasma surrounds the component, which means it does not need not to be manipulated inside the chamber to get an even and uniform coating.

"The ion energy can be varied as can the composition of the gases in the chamber to vary the properties of the coating."

It is hoped DLC will also be useful for coating industrial equipment, such as drills and car parts.


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