Antimicrobial Decorative finishes

By Ian Desmond

Can a decorative finish kill bacteria too? We look at some of the old and new technology that does exactly that.

Can coatings add more to surfaces than durability and decoration?

The answer is yes – not only can the surface of a countertop look more attractive or the handle on a fridge look like chrome – but coatings applied using the PVD process can help fight invisible germs. This is done by incorporating antimicrobial additives into the hard surface coating.

Killing infection in hospitals and clinics

Repeated testing reliably concludes that these coatings can be effective in helping to kill organisms that commonly grow on various kinds of surfaces, which include door knobs and handles, handrails, taps and many more fixtures and accessories. These surfaces are often touched by people at work or in everyday life, especially in hospitals and clinics and can result in the spread of germs and bugs or the dreaded hospital re-infections.

Silver as an antimicrobial substance

That are several substances that pack a real punch in the fight against bacteria. There are several known examples where the use of silver has led to an extraordinary toxicity for bacteria. Its disinfectant properties for hygienic and medicinal purposes have been known since ancient times and it has been used to prevent wound infection since World War I.

Bacteria under the microscope

Bacteria under the microscope

Using nanotechnology in antimicrobial science

Nanotechnology is about particles with a size of few nanometres. One nanometre (nm) is one billionth, or 10-9 of a metre. Nano particles and nano-structures are composed of only a few atoms or molecules. By using structures at nanoscale as a physical variable, we can greatly expand the range of performance of existing chemicals and materials. Surfaces coated with nanotechnology, which varies according to the product, are extremely stain-resistant, scratchproof and can be self-cleaning and antibacterial. Something that sounds like sci-fi fantasy is also they can clean our air from nitrogen oxide and organic fine dust.

There is an increasing interest in using silver- and nanosilver – coated materials for medical environments. The silver compounds used for these surfaces vary and may range from elemental silver to complex silver coatings. Using the PVD technique, an ion beam deposition process can be used to apply silver as a continuous silver coating (layer thickness of around 1200 Å (Ångström) = 0.12 μm).

Titanium dioxide coating

New technology is emerging all the time and new antimicrobial and self-cleaning titanium dioxide coatings have emerged. The titanium dioxide used in some of the newest products is photocatalytically active. It forms oxygen radicals on its surface, if it is irradiated by light. The activated oxygen decomposes molecules and organic dirt particles that contact the surface.

The photocatalytic ability of the coating gives therefore an antimicrobial effect. Normal daylight is entirely sufficient and even artificial light in inner rooms is enough to activate the process of photocatalysis.

The antimicrobial ability is seen by comparing the gradual change in characteristics of two cultured E. Coli populations under UV, one on a coated surface, the other on a neutral surface.

Ion plating to produce TiO²

In more research, there was an experiment involving an arc ion plating method to produce TiO² film on medical grade stainless steel. The results? This provides an effective antimicrobial surface coating method for medical implements thereby reducing the risk of hospital-acquired infections.

The new coatings can lead to new designs of knee and hip implants and substantially reduce the number of costly revision surgeries faced by patients undergoing hip and knee replacements.

These coatings reduce friction and wear, extend device lifetimes and achieve high levels of biocompatibility with their excellent bug-blasting properties. It’s nanotastic!