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A plastic covering that can be shrink-wrapped onto surfaces in hospitals, kitchens, and just about anywhere pathogens gather acts as a repellant and can go a long way in combatting superbugs, its inventors claim. Investigators with McMaster University created a flexible plastic wrap that’s textured with microscopic wrinkles to block external molecules, in a study published in ACS Nano.
The surface, working through a combination of nanoscale engineering and chemistry, takes its cue from the water-repellent lotus leaf. A drop of water or blood bounces off it, say the inventors, one of whom is engineering physicist Leyla Soleymani. “We’re structurally tuning that plastic,” she says in a press release. “This material gives us something that can be applied to all kinds of things.”
The McMaster team created 3 classes through this wrinkling process: micro-structured, nanostructured (self-assembly of nanoparticles), and their combination (hierarchically structured).
“We found that hierarchical structuring provides superior hydrophobicity and oleophobicity with water contact angle of above 150°, blood contact angle of above 140, hexadecane contact angle of above 110°, and sliding angles lower than 5°,” the study states.
Hydrophobicity is what makes some molecules repel water. Oleophobicity is the property in a molecule that makes it repel oils.
Investigators tested the material on methicillin-resistant Staphylococcus aureus (MRSA)
and Pseudomonas aeruginosa, noting that these hospital-acquired infections are often fatal, with a 90-day mortality rate of 21% for MRSA and 19% for P. aeruginosa in US hospitals.
“All of the surfaces included a fluorosilane treatment for enhancing their hydrophobicity and oleophobicity; however, omniphobic behavior was not observed with microstructured or nanostructured surfaces even with the fluorosilane treatment,” the study states. “The omniphobicity originates from the stable Cassie state and the increased air pockets trapped beneath the liquids contacting the hierarchical surfaces for both low and high surface tension liquids.” They describe the Cassie state as a robust omniphobicity without the use of lubricant due to the entrapment of air pockets within the structures.
To understand how well the surfaces repelled bacteria, the investigators created a touch-assay. “We showed that the application of this hierarchical omniphobic surface onto everyday items and medical devices reduced the transfer of Escherichia coli onto these objects from a contaminated agar plug,” the study states. LessE. coli was transferred to human skin that came into contact with the contaminated hierarchical surfaces compared to contaminated control surfaces.
“Our hierarchical wraps could easily be applied onto various surfaces in hospitals that are commonly contaminated with bacterial pathogens such as, doorknobs, bed tables, bed rails, and other high-risk surfaces,” the study states. “Additionally, since the hierarchical surfaces are fabricated through all- solution-processing, they would be amenable to large area applications and large volume manufacturing, being applicable to a wide range of surfaces that have a risk of being in contact with liquid-borne contaminants.”