This antibacterial stainless steel could stop the super-bacteria plague

A team of Georgia Tech University scientists have designed a steel-and copper-based material that doesn’t need to be treated with detergents or antibiotics to remain bacteria-free. This unique property is the product of its surface geometry, which is etched with nanoscopic needles so small and sharp that they pierce bacteria’s cell wall, effectively killing it without the need for sterilization.



This is a potentially revolutionary invention, as bacterial infections have become a major challenge for global health. The abuse of antibiotics and other chemicals have caused some bacteria to become lethal. As the researchers note in their study, published in the nanotechnology scientific journal Small , new antibiotic-resistant variants of bacteria directly caused the deaths of 1.27 million people worldwide in 2019, and they contributed to almost 5 million additional deaths.



“Bacteria can grow rapidly, especially in shared settings. The point of this work is to reduce the drug resistant bacteria,” postdoctoral scholar and lead researchers Dr. Anuja Tripathi told me in an email interview. “We demonstrated that dual activity of copper coated nanotextured steel can compromise the bacteria by rupturing the cell membrane and membrane depolarization, without any chemical.”



This metamaterial won’t have the same evolution-overdrive effect caused by antibiotic chemicals. While bacterias can mutate to adapt to antibiotics, their membranes can’t adapt to physical tearing, in the same way animals can’t adapt to bullets piercing through their bodies.



Tripathi and her team claim that their invention can be used to make objects that are antibacterial in nature for use in hospitals and kitchens, where contamination of a surface can lead to serious illnesses. Their tests involved E. coli and staphylococcus, which represent the main two groups of bacteria respectively: gram-positive (which, roughly, are protected by a wall of amino acids and sugars called peptidoglycan and one inner membrane) and gram-negative (which are protected by layers of peptidoglycan sandwiched between two membranes).



“Killing Gram-positive bacteria [which have thinner cell walls] without chemicals is comparatively easy, but tackling Gram-negative bacteria poses a significant challenge, due to their thick, multilayered cell membrane. And if these bacteria persist on surfaces, they can grow rapidly,” Tripathi explains. The reseachers’ goal was to develop an antibiotic-free bactericidal surface that would be effective against gram-negative and gram-positive bacteria alike.



During the Tripathi’s electrochemical process, current and an acid electrolyte etch nano-sized needle-like structures on the surface of stainless steel. The structures are able to destroy bacterial cells. [Photo: Courtesy Anuja Tripathi]



Designing a cleaner metal



The metamaterial is manufactured using a two-step electrochemical process that modifies the surface of stainless steel. First, the process etches the steel into structures similar to long needles of nanoscopic size. The second part consists of depositing an atomic-thick layer of copper ions on the surface.



Tripathy says that the stainless steel nanotexture kills all types of bacteria on its own, but her team wanted to further increase the antibacterial activity using copper. While copper has long been known for its anti-bacterial properties, it’s too expensive to use in large quantities. The team discovered that only a few copper ions needs to be deposited on the steel to have the same antibacterial effectiveness, thus avoiding the prohibitive cost of using copper in the large scale manufacturing of countertops, tables, surgical equipment or door knobs.



The study demonstrated that modified stainless steel shows remarkable antibacterial activity, reducing 97% of E. coli and 99% of staphylococcus. This doesn’t mean you can skip cleaning surfaces. Tripathi tells me that cleaning is still necessary because this surface requires direct contact to kill bacteria. “Any contaminants present will reduce the contact between bacteria and the metal surface, as bacteria can quickly proliferate, especially in shared areas like staircases and door handles where they may commonly spread,” she says. You only need to keep the surface clean with a cloth and water for the steel to work its magic.



That’s the key here. Since the nanotextures on these surfaces compromise bacteria without any chemicals or antibiotics, this reduces the risk of bacterial spread and the development of drug-resistant bacteria, which are notoriously difficult to eradicate, Tripathi says.



These four samples of stainless steel show the different stages of Tripathi’s process. At left, an unmodified sample at the top and a sample after the electrochemical etching process at the bottom. On the right, two samples after copper ion deposition — four minutes for the top piece and 15 minutes for the bottom piece. [Photos: Courtesy Anuja Tripathi]



Stopping the plague



Tripathi says the copper coating will eventually wear off. “We tested copper leaching over 80 days and observed a reduction of about 27%,” she says. But that isn’t a problem thanks to the efficacy of the underlying steel surface, which on its own can compromise bacterial cells, ensuring the material remains antibacterial throughout its lifetime.



The team wants to do more research to check the effectiveness of the new nanotextured steel against other harmful bacteria, but Tripathi tells me that the metamaterial will work with other strains and types, as they share the same cell wall characteristics that are vulnerable to the same mechanics.



If the development continues in the same direction, this new steel may become a staple in medical environments and everywhere else. Frequently touched surfaces, like door handles and stair railings, will benefit from this. There is also interest in bringing it to medical implants to prevent infections. From there, the cost might be cheap enough that it could extend to the food industry, from containers to pots and pans to surfaces in large food processing factories, which seem prone to E.coli outbreaks . You could also imagine consumer electronics brands like Apple and Samsung using some form of this steel to create bacteria-proof phones and gadgets. After all, fear is an extremely powerful sales point .