Bacteria see etchings, and die

Materials scientists have devised a process that causes bacteria to explode while leaving mammalian cells unaffected.

The process – described in the journal ACS Biomaterials Science & Engineering – opens the door to potentially eliminating infection risks associated with implantable medical devices and food processing equipment.

A team led by Yeongseon Jang from the School of Chemical and Biomolecular Engineering at the Georgia Institute of Technology, US, devised a method of using nano-scale electrochemical etching on the grade of stainless steel typically used for making medical and food-preparation devices.

In testing, the patterns created proved effective in killing both Gram negative and Gram positive bacteria (Escherichia coli and Staphylococcus aureus, respectively), while leaving mammal cells unharmed.

The different outcomes for the two types of cells is easily explained – mammal cells are an order of magnitude larger than bacterial ones – but the reason why the etched surfaces are lethal to the microbes is not yet fully understood.

Electrochemical processing is usually used to polish and smooth out the surfaces of steel. Jang’s team, however, discovered that by varying both the current and the voltage passed through the steel the technique could produce the opposite result – making the surface rougher, albeit on a nano scale.

In their paper, the researchers speculate that the affected surface is characterised by nano-sized spikes and other nasty, pointy shapes upon which the bacteria impale themselves, rupturing catastrophically.

“It’s like a mountain range with both sharp peaks and valleys,” says co-author Julie Champion. “We think the bacteria-killing effect is related to the size scale of these features, allowing them to interact with the membranes of the bacterial cells.”

The discovery, which has wide potential for use in fields where antimicrobial surfaces are needed, grew out of an earlier research project conducted by the team. The initial idea was to create super-water-repellent surgical steel that would effectively repel bacteria at the same time.

It soon became clear, however, that doing this would require the use of chemical coating, an outcome the scientists didn’t want. Jang and colleague Won Tae Choi then proposed the etching idea, and the team set about putting it to the test.

Although the work so far has been bench-based, the researchers see few if any hurdles in converting it to industrial levels.

“In principle, this is very scalable,” says team member Dennis Hess. “Electrochemistry is routinely applied commercially to process materials at a large scale.”