New Steel Kills Bacteria With Nanospikes

Nanospikes trapping bacteria

Anti-bacterial stainless steel has been discovered by researchers at the Georgia Institute of Technology in the USA

An electrochemical etching process is used to turn a common stainless steel alloy into a bacteria-killing surface that remains harmless to touch! This treatment creates a surface of tiny spikes and other nano-protrusions that are invisible to the naked eye. These spikes are too small to affect mammalian cells but large enough to prove inhabitable for bacteria.

Close-up image shows an untreated stainless steel sample (left), and a sample that has been electrochemically treated to create a nanotextured surface. The sample was prepared by using a potentiostat in Professor Preet Singh's laboratory at Georgia Tech. Credit: Rob Felt, Georgia Tech

Close-up image shows an untreated stainless steel sample (left), and a sample that has been electrochemically treated to create a nanotextured surface. The sample was prepared by using a potentiostat in Professor Preet Singh’s laboratory at Georgia Tech. Credit: Rob Felt, Georgia Tech

“[You] cannot tell the tactile difference between untreated and nanotextured stainless steel surfaces by hand because the nanotextures are relatively too small,” study author Won Tae Choi told Gizmodo.

Tests were done with Escherichia Coli and Staphylococcus Aureus. Results show that the surface modification killed both gram-negative Escherichia coli (E.coli) and gram-positive Staphylococcus aureus (Staph) bacteria. Both of which are notorious for being harmful and drug-resistant If further research proves accurate, implantable medical devices and food processing equipment may be nanotextured so their surfaces can attack microbial contamination by puncturing bacterial membranes to kill the bugs.

The initial goal was to create a superhydrophobic surface on the stainless steel in an effort to repel liquids – and with them, bacteria. To create such a surface would require a chemical coating, something the researchers wished to avoid. An alternative idea was proposed by postdoctoral fellows Yeongseon Hang and Won Tae Choi to use a nanotextured surface.

Centers for Disease Control and Prevention, public domain, via Wikimedia Commons Lab test results showed that, for at least 48 hours, the surface could bounce off both gram-positive Staphylococcus aureus and gram-negative Escherichia coli, each of which are notorious for being harmful and drug-resistant.

Centers for Disease Control and Prevention, public domain, via Wikimedia Commons
Lab test results showed that, for at least 48 hours, the surface could bounce off both gram-positive Staphylococcus aureus and gram-negative Escherichia coli, which are notorious for being harmful and drug-resistant.

Experiments with varying levels of voltage and current flow in a standard electromagnetic process were conducted by the team. Normally, an electromagnetic process is used to polish stainless steel. This time it was used to toughen the surface at the nanometer scale by Champion and collaborator Dennis Hess – a professor and Thomas C. DeLoach, Jr. Chair of the School of Chemical and Bionuclear Engineering.

“Under the right conditions, you can create a nanotexture on the grain surface structure,” Hess explained. “This texturing process increases the surface segregation of chromium and molybdenum and thus enhances corrosion resistance, which is what differentiates stainless steel from conventional steel. Microscopic examination showed protrusions 20 to 25 nanometers above the surface. “It’s like a mountain range with both sharp peaks and valleys,” said 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.”

“This surface treatment has potentially broad-ranging implications because stainless steel is so widely used and so many of the applications could benefit,” said Julie Champion, an associate professor in Georgia Tech’s School of Chemical and Biomolecular Engineering. “A lot of the antimicrobial approaches currently being used add some sort of surface film, which can wear off. Because we are actually modifying the steel itself, that should be a permanent change to the material.”