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Clean touch: germ-free plastics

They are a convenient way to produce soft coatings for metals, glass and ceramics that are UV-resistant and can even provide protection against corrosion. Since there is a choice of high-gloss, matt, smooth or structured surfaces and the material can in addition have whatever colour is needed, decorative requirements can be met too.

Research scientists from the University of Massachusetts have adopted an innovative approach: they have developed polymers that imitate naturally antimicrobial substances (peptides), i.e. the compounds that form the first line of defence against infections in human beings and animals.

The scientists found an ingenious way to do this: instead of imitating the peptides chemically, they just copied their surface structure. As soon as a microbe latches onto the plastic now, the latter perforates its cell membrane and the germ dies. The potential applications range from antiseptic kitchen tables to the equipment used in operating theatres.

Clean touch: germ-free plastics


Products made from practically all materials and used in practically all areas of life are being given better antimicrobial properties in the meantime. Measures taken to eliminate germs in the food industry, such as coatings for the inside of beverage cans, extend shelf life and help to economise on preservatives that can cause allergies. Making socks, shoe inlays, mattresses or upholstered furniture germ-free prevents unpleasant odour formation, for which bacteria are responsible that interact with the sweat.

The demand for antimicrobial plastic is probably strongest in the medical community. Wound dressings contain silver additives that are found in a similar form in the plastic containers used to store contact lenses too. Clinical studies have shown that catheters with a silver sulfadiazine coating can reduce vein infection rates by almost a factor of 5.

In orthopaedic engineering, silver has recently been introduced as an antibacterial substance in the plastic shafts of prosthetic limbs, in order to counter odour formation and inflammation. According to the manufacturer, the technology reduces colonisation by the bacterial strains Staphylococcus aureus and Escherichia coli by 99.9 per cent.

Last but not least: a self-disinfecting film that can be stuck, for example, to door handles and sanitaryware is an effective way to prevent germs from being passed on in hospitals. It has been developed at the Institute for Chemistry and Bioengineering Sciences at Zurich Technical University (ETH) in Switzerland.

The film is coated with silver and calcium phosphate; according to ETH, the combination of both substances is up to 1,000 times more deadly to Escherichia coli than conventional silver products. The background: calcium phosphate is a welcome food source for the bacteria, which consume it eagerly.

When the substrate material breaks down, the integrated silver particles are released; they have a toxic effect on the bacteria, however, so that the latter can be depended on to eat themselves to death by consuming the calcium. In other words, the crucial feature of the process is that the bacteria initiate the germicidal effect themselves and in fact control it, because silver is only released to the extent that bacteria are present to consume the calcium phosphate.

Read more: Plastics 535