Slippery steel that repels bacteria

A new coating for steel that reduces contaminants sticking to it has been developed by researchers at Harvard University.

Corrosion and contamination can occur when steel comes into contact with liquids. To prevent this, a coating is often applied before use. This coating must be able to protect the steel without reducing its strength.

A combination of a lubricant, to repel the liquid, and the compound tungsten oxide, to secure the lubricant to the steel, has been used before by the group to create "slippery" steel.

However, although the tungsten oxide is able to secure the lubricant to the steel surface, it is a ceramic and so will crack easily if formed as an even layer, exposing the bare metal beneath.

By changing the way this layer is applied to the steel, Joanna Aizenberg and her team have been able to avoid this problem.

The ceramic layer is usually deposited onto the steel by applying a voltage to it when it's submerged in a tungsten oxide solution.

In this study, by applying the voltage in pulses, they were able to fix the tungsten oxide to the steel in small islands.

The gaps between these islands give the steel more flexibility and enable it to bend without damaging the ceramic layer, the group reported in Nature Communications this week.

When the lubricant is applied, it binds to the top of the islands and the sides of them, creating a protective coating that covers the whole surface of the steel.

Interestingly, the treated scalpel also cut much more smoothly than a traditional one.

This new style of coating showed reduced adhesion of both blood and the bacterium E. coli when tested on a surgical scalpel.

It also repelled algae, and so if this new deposition method is scaled up, it could be used for marine applications as well.

To test how durable this new method of coating was, the researchers used tape to try and pull off the layers and tested its strength at different temperatures.

The layer remained fixed to the surface during these tests, an important feature as it prevents the lubricant entering the environment surrounding the steel.