Georgia Tech researchers forge copper-infused, nanotextured stainless-steel material to stem rising tide of deadly infections.

Researchers at Georgia Institute of Technology have created a stainless-steel alloy infused with copper to prevent bacterial infections caused by surface contamination.

The new metal has potential to be used to create an effective, scalable, and sustainable solution to the growing threat of deadly antibiotic-resistant microbes adhering to surfaces in hospitals and other shared settings.

Derived from an electrochemical process developed at Georgia Tech's School of Chemical and Biomolecular Engineering, the alloy capitalizes on the natural antibacterial properties of copper and creates tiny needle-like structures on the surface of stainless steel to kill harmful bacteria like E. coli and Staphylococcus.

The researchers say the process is convenient and inexpensive and could reduce the need for chemicals and antibiotics in hospitals, kitchens, and other settings where surface contamination can lead to serious illness.

It also has the potential to save numerous lives.

A global survey shows that in 2019, antimicrobial resistant infections killed more people than HIV/AIDS or malaria, directly responsible for the deaths of 1.27 million people and contributing to nearly 5 million others, making these infections one of the leading causes of death for every age group, according to an article published in 2022 in Nature.

The shiny surfaces commonly seen in hospitals and restaurants, however, do not have a natural defense against bacteria that cause infections.

"Bacterial adhesion to stainless steel, an alloy commonly used in shared settings, numerous medical devices, and food and beverage sectors, can give rise to serious infections, ultimately leading to morbidity, mortality, and significant healthcare expenses," the Georgia Tech research team said. "The presence of harmful microorganisms on the surfaces we touch every day, especially in healthcare settings with vulnerable patients, necessitates new approaches to control bacterial contamination and the spread of infection."

Treating hospital surfaces with disinfectants has addressed this concern to a certain degree, but continuous usage of antibacterial agents can lead to development of drug-resistant bacteria.

"Nanotextured stainless steel that incorporates inherent antibacterial materials, such as copper, can exhibit dual antibacterial properties," the Georgia Tech research team wrote. "The dual antibacterial activity is due to the small grooves and ridges on the nanotextured surface, which make it difficult for bacteria to attach and spread, and release of copper ions that kill or inhibit the growth of bacteria.

The scientists described the new copper-stainless steel alloy, along with the process developed to create it, in a research paper published in the May 20 edition of the journal Small.

"In this study, we fabricated nanotextured stainless steel and subsequently coated it with copper using inexpensive, scalable electrochemical techniques for both steps," they wrote. "This approach offers several advantages, including dual-antibacterial properties, affordability, scalability, eco-friendliness, and precise control of surface structures through electrochemical parameters such as potential and current density."

The team has demonstrated that the copper-coated nanotextured stainless steel fabricated with an electrochemical process is effective as an antibiotic-free biocidal surface to combat both gram-positive and negative bacteria.

"Killing Gram-positive bacteria 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," observed Anuja Tripathi, lead author of the study and a postdoctoral scholar in Georgia Tech's School of Chemical and Biomolecular Engineering.

"I aimed to develop an antibiotic-free bactericidal surface effective against Gram-negative and Gram-positive bacteria," she added.

Tripathi and her colleagues, William R. McLain Professor Julie Champion and former Ph.D. students Jaeyoung Park and Thomas Pho, produced the material, which does not help bacteria develop resistance to drugs.

Inexpensive technique

The scientists developed an electrochemical method to etch stainless steel, creating nano-sized needle-like structures on the surface capable of puncturing the cell walls of bacteria. Then, with a second electrochemical process, the researchers deposited copper ions on the steel's surface.

Candler Hobbs

During Tripathi's electrochemical process, current and an acid electrolyte etch nano-sized needle-like structures capable of destroying bacterial cells on the surface of stainless steel.

The copper interacts with the bacteria's cell membranes and compromises them.

"The nanotextured stainless steel can kill both Gram-negative and Gram-positive bacteria, but we wanted to enhance the antibacterial activity for surfaces that can be highly contaminated," Tripathi explained. "The copper coating on the nanotextured stainless steel gave us very high antibacterial activity. As nanotexture and copper combine for dual methods of killing, this material should not contribute to drug-resistant bacteria as antibiotic use does."

The team's approach involved applying a copper coating to nanotextured stainless steel, resulting in an antibacterial activity within 30 minutes.

The researchers found that copper-coated nanotextured stainless steel induces a remarkable reduction of 97% in Gram-negative Escherichia coli and 99% Gram-positive Staphylococcus epidermidis bacteria.

They concluded that the material has potential to be used to create effective, scalable, and sustainable solutions to prevent bacterial infections caused by surface contamination without contributing to antibiotic resistance.

"We have demonstrated dual-activity surfaces for killing bacteria using copper-coated nanotextured stainless steel. We achieved this by employing an inexpensive electrochemical technique to first create nanotextured surfaces on SS316L, featuring nanopores and nano protrusions measuring 20–30 nm (nanometers), then deposit copper onto the nanotextured surface, resulting in globular or thin film morphology. Both the copper-coated nanotextured stainless steel and the bare nanotextured stainless steel displayed enhanced antibacterial qualities compared to regular stainless-steel surfaces," Tripathi wrote.

"Although copper will gradually leach out from the metal over time, the underlying nanotextured stainless steel structure will remain intact, ensuring that the surface retains antibacterial attributes even after the copper has been released," she added.

This advancement has significant potential for practical usage, as it offers a method to prevent bacterial adhesion and surface contamination without antibiotics, and a similar process, electrochemical polishing, is already used at scale to smooth large and small steel products. Further, the dual function may not contribute to development of drug-resistant bacteria like antibiotics do, according to the researchers.

The cost-effectiveness and scalability of this surface modification approach may potentially make it relevant for larger-scale surfaces in public or healthcare settings, they added.