From hospitals to kitchens, this transparent and flexible shrink wrap could protect against antibiotic-resistant superbugs by not letting anything stick to it. It is both hydrophobic and oleophobic (omniphobic), and that lets it repel all kinds of liquid contaminants, no matter whether they are water-based or oil-based. Bacteria and biofilms also have trouble attaching themselves to wrapped surfaces.
The secret is in creating microscopic soft wrinkles.
Inspired by the microstructure of naturally water-repellent lotus leaves, McMaster University engineers Leyla Soleymani and Tohid Didar designed this flexible wrap to be applied over existing surfaces that are prone to contamination, like door handles and stethoscopes. Their study was published in ACS Nano.
Previously, most omniphobic surfaces were created with lubricants, but the lubricant layer has to stay intact for the surfaces to stay repellent. That makes them vulnerable when used in dry open air, and they can’t be cleaned without risking wiping off the lubricant.
Wrinkles on a nano- or microscale can provide the same omniphobicity without a lubricant by introducing tiny air pockets. However, many processes used to create them, like photolithography or electrospinning, can be hard to scale up; higher volume processes like laser ablation require physical and chemical processing steps that mean the end product can’t be flexible, and that would require complete replacement of existing surfaces.
The new material addresses these limitations by combining a soft wrinkled structure with chemical modifications to help repel more bacteria. The resulting flexible wrap can be applied over existing surfaces to limit bacterial transfer.
Starting with pre-strained polyolefin, microstructured wrinkles were induced by exposure to Ultraviolet-Ozone. The wrinkled surface was treated with fluorosilane to make it more hydrophobic, and then modified into an even more textured nanostructured surface by depositing colloidal silica nanoparticles.
The material’s ability to repel a variety of liquids was demonstrated using pure water, hexadecane, and whole human blood; repellency was maintained even when the material was bent over a curved surface, subjected to a vacuum for three hours, or covered in bleach for two hours. That means it can be shrink-wrapped over complex surfaces, repel liquids when used in open air, and hold up under cleaning by harsh disinfectants.
Compared to unmodified planar polyolefin, the modified polyolefin wrap saw an 85 percent reduction in biofilm formation by P. aeruginosa and MRSA, two clinically relevant pathogens commonly found in hospitals.
Reduced bacterial transfer was also demonstrated by touching a wrapped surface with an agar plug contaminated with fluorescent E. coli; very little signal was observed on the wrapped surface, and even less was subsequently transferred to a human hand by touching the contaminated area.
“We can see this technology being used in all kinds of institutional and domestic settings,” said Didar in a press release. “As the world confronts the crisis of anti-microbial resistance, we hope it will become an important part of the anti-bacterial toolbox.”