Implantable medical devices such as cardiac stents, hip replacements and pacemakers can all be vulnerable to bacterial contamination which may be damaging to patient health. To combat this issue, researchers at the Georgia Institute of Technology have used an electrochemical etching technique to create stainless steel samples with an antimicrobial nanotextured surface.
According to the researchers, the nanoscale spikes on the surface of the treated metal alloy likely puncture bacterial membranes, preventing pathogens from being able to grow and proliferate on the material. The nanotextured stainless steel appears to be harmless to mammalian cells – an important factor if the technique is to be used in the future to treat medical devices destined for implantation.
The material’s resistance to corrosion also seemed to improve after it was treated using the electrochemical etching process, which could be another big benefit for medical device manufacturers. The research team published the details of their work in the journal ACS Biomaterials Science & Engineering.
“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.”
The nanotextured surface appeared to be effective at eliminating both Gram-negative bacteria, such as Escherichia coli, and Gram-positive strains, including Staphylococcus aureus. When the modified metal samples were exposed to mouse cells, however, they had no toxic effects, suggesting that mammalian cells could still bind to the medical implant and prevent post-surgical rejection.
While the researchers originally wanted to create an ultra-hydrophobic surface which would repel bacteria from being able to adhere to the device, they quickly realized that this would require the use of a chemical coating which Champion and her colleagues were trying to avoid. They then explored using an electrochemical process – which is commonly used to polish stainless steel – to add a rough texture to the surface.
“Under the right conditions, you can create a nanotexture on the grain surface structure,” said Dr. Dennis Hess, a professor and Thomas C. DeLoach, Jr. Chair in the School of Chemical and Biomolecular Engineering. “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.”
The surface that resulted from the etching process shows 20 to 25 nanometer high protrusions on the metal alloy. According to the researchers, because this process relies upon a biophysical change as opposed to the addition of a chemical, bacteria should not be able to develop a resistance to the roughened 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”
According to Hess, the technology is easily scalable and could also have applications in preventing the growth of foodborne pathogens on equipment used in food manufacturing. Longer-term studies will need to be conducted in order to determine how well the nanotextured surface retains its integrity when exposed to wear, and whether any toxicities toward mammalian cells may reveal themselves over time.