In a study published in the Proceedings of the National Academy of Sciences (PNAS), lead co-authors Joanna Aizenberg, Alexander Epstein and Tak-Sing Wong coated solid surfaces with an immobilized liquid film so bacteria cannot grip and grow together into biofilms.
The technology, called SLIPS (Slippery-Liquid-Infused Porous Surfaces), creates a hybrid surface that is smooth and slippery due to its liquid layer.
Biofilms are hard to remove pathogens that get stuck on machinery and other surfaces in manufacturing plants.
They form a tough surface skin that resist conventional commercial washing and sanitizing methods and become constant sources of contamination, resulting in lowered shelf-life of products and potential consumer illness.
How it works
Aizenberg, Amy Smith Berylson Professor of Materials Science at the Harvard School of Engineering and Applied Sciences (SEAS) and a core faculty member at the Wyss Institute for Biologically Inspired Engineering at Harvard said the surface infuses a porous solid matrix with a lubricating fluid.
“The fluid forms a smooth, flat lubricating layer over the whole surface, and remains stably attached by adhering to the pores,” she told FoodProductionDaily.com.
“The liquid layer forms a highly slippery surface that bacteria cannot attach to.
“Specifically, since the liquid surface consists of molecules that are highly mobile, permanent interactions between bacteria and the surface cannot be easily established.”
She added there are a number of methods to apply SLIPS onto industrial metals, such as aluminium, which is commonly used for machinery and surfaces in food processing and packaging facilities.
Aizenberg said one of the issues they faced was to determine the "right" lubricating fluid for the material, as it had to be immiscible with the aqueous environment, have low toxicity and be bio-compatible.
The researchers noted chemical coatings, antibiotics and textured surfaces have all been used to try and deter biofilm build up.
“Conventional anti-biofouling materials are in solid form, where the surface atoms [and] molecules are static and would lead to permanent interactions with bacteria over time (i.e., strong surface adhesion),” said Aizenberg.
“As a result, conventional solid-state anti-biofouling materials are non-ideal in preventing long-term biofouling.”
The researchers have shown that SLIPS prevents 99.6% of Pseudomonas aeruginosa biofilm attachment over a seven day period, as well as Staphylococcus aureus (97.2%) and Escherichia coli (96%), under both static and physiologically realistic flow conditions.
“This is approximately 35 times the reduction of attached biofilm versus best case scenario, state-of-the-art PEGylated surface, and over a far longer timeframe.”
The next step
In future studies, the researchers aim to better understand whether any bacteria transiently attach to the interface and then slip off, if they float above the surface, or if any remain loosely attached.
“The ability to effectively apply SLIPS onto surfaces of any materials and any geometrical shapes at low cost would be ideal for large scale industrial applications.
“We are in the process of optimizing our SLIPS fabrication processes, and we expect to see some SLIPS-related products for specific applications fairly soon.”
She added the hope is that SLIPS will provide a low-adhesion, easy-clean surface to remove germs or pathogenic contamination, reducing the risk for disease spreading in a variety of applications.
Source: Proceedings of the National Academy of Sciences (PNAS)
Published online ahead of print, doi: 10.1073/pnas.1201973109
“Liquid-infused structured surfaces with exceptional anti-biofouling performance”
Authors: Alexander K. Epstein, Tak-Sing Wong, Rebecca A. Belisle, Emily Marie Boggs and Joanna Aizenberg.