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Copper: Man’s oldest metal now has its day.

Issued at 2011-02-09



Copper is a powerful antimicrobial with proven broad-spectrum efficacy against bacteria, viruses, fungi and moulds. Clinical trials in hospitals around the world have confirmed the benefit of deploying copper touch surfaces to reduce microbial contamination, and now manufacturers are beginning to develop products to serve this new market. Mark Tur, Copper Development Association’s technical consultant, explains more.

Copper is widely considered to be man's oldest metal, deriving this accolade from the first use of cast bronze in cultures about 5,000 years ago,  from which the name ‘Bronze Age’ arose. Subsequently, copper alloys have been developed to serve an enormous range of applications based upon its key properties: aesthetics, strength and corrosion resistance, electrical or thermal conductivity and relative ease of manufacture. However, a property apparently overlooked for 4,000 years is bringing the focus back on to copper in the 21st century: its antimicrobial characteristics.

The oldest known written record of copper being employed to fight infection was found in the Edwin Smith papyrus, which has been dated at about 1,600 BC, although it is probably a transcription of a much earlier document dating from around 3,000 BC. At about the same time, Greek legend tells of Achilles curing Telephos by scraping the ‘rust’ from his spear into a battlefield wound – clearly this would have been a cast bronze spear point.

About 30 years ago, the germ-beating properties of brass were revisited when Dr Phyllis Kuhn carried out a survey of door handles in her hospital in Pennsylvania. She showed that brass door handles had almost no live bacteria whilst stainless steel was a reservoir for infection. This led to a series of laboratory studies – many carried out at the Environmental Health Unit at Southampton University – and the publishing of a series of peer-reviewed papers.

It has been found that most commercially-important alloys have these characteristics, and independent verification of the properties has led to the US Environmental Protection Agency (EPA) permitting the registration of nearly 300 grades of copper and its alloys as having antimicrobial efficacy. It is the only solid material to be thus confirmed. Alloys and products complying with strict usage conditions can be distinguished by a Cu+ mark, developed and overseen by the International Copper Association (ICA) to denote antimicrobial copper products.

So, how quickly does this antimicrobial effect occur? This depends upon circumstances and testing methods.  The most commonly-used laboratory test is one developed in Japan (JIS Z2810), or the more recent ISO 22196, which is based upon it. However, these tests do not represent the typical conditions found inside a hospital ward as they are carried out at 100% humidity and 37°C. A more appropriate test was developed by Professor Bill Keevil at Southampton University. This allowed testing under the typical room atmosphere of 25°C and 50% humidity, or any other combination of temperature and humidity.

Using this protocol, it was shown that stainless steel and silver-containing materials were ineffective whilst copper showed a complete kill in 90 minutes. So what? Ninety minutes is a long time on a busy hospital ward. In fact, these test conditions were based on a very large dose of bacteria being applied to the test sample: some one billion bugs. When the test was repeated with a level more usually found in hospitals – 1000 bugs per cm2 – the kill time was reduced to less than 15 minutes, and subsequent refinement of laboratory tests has shown kill times in the order of just one or two minutes.

The laboratory work is ongoing as scientists attempt to match typical contamination events with a suitable, repeatable and comparable laboratory test. More practical, and possibly even more compelling, are the results from clinical trials, the first of which was carried out at Selly Oak Hospital in Birmingham under consultant microbiologist Professor Tom Elliott. In a series of investigations carried out over a period of three years, the replacement by copper and copper alloys of the more usual plastic, anodised aluminium, chromium plated diecastings, or stainless steel has been evaluated. The first medium-term test showed better than 90% fewer microbes on the copper alloys than on controls. This work has been verified by similar clinical trials in Chile and the USA, and further work is being carried out in Finland and Japan.

The most complex components replaced during the clinical trial at Selly Oak were the mixer taps: already manufactured in CuZn39Pb1 leaded brass by gravity die casting, but finished in-house by chromium plating.  It was an easy intervention for a UK-based manufacturer to take the polished units out of the manufacturing sequence before plating. This alloy was chosen because the complex internal details were cast to near-net-shape and readily machined where necessary for seatings and seals. Other internal components were machined from compatible brass machining rods.

In seeking to develop novel technology to allow manufacturers to near-net-shape whilst reducing material content – and therefore cost – ICA has co-funded a project to investigate a process called HeatForm. This is a hot development of hydroforming whereby hollow tube, or other preform, is shaped in a suitable mould using high-pressure air. Results so far have allowed reduced weight whist allowing complex forms to be made with excellent surface finishes. Whilst still at an early stage, HeatForm shows considerable promise as a commercial process.

The return to the use of copper alloy components in hospital environments has already started with early adopters in Ireland and the UK. In January 2010 there was news that Saint Francis – a private hospital in Mullingar, Ireland – was the first hospital in the world to replace door furniture with antimicrobial copper components to help fight infection. This has been followed by the Sheffield Cystic Fibrosis Clinic, where patients at high risk of infection are benefitting from copper’s ability to kill potentially dangerous pathogens, reducing the risk of picking them up from touch surfaces.

A clinic in Chiba, Japan went so far as to install brass sheet on the walls, meeting the architect’s aesthetic requirements as well as conferring antimicrobial benefits. Most recently, in Pori, Finland, a recently-opened medical facility has introduced copper floor drains and covers made from deep-drawn copper. It was considered important to help control the growth of organisms in challenging, high-humidity environments by implementing copper, so these have been used in toilets and shower rooms.

For more information on antimicrobial copper, including recognised alloys, scientific data, markets and applications, visit www.antimicrobialcopper.com


Source: Foundry Trade Journal



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