Biofilm Coating: Defense Strategy for the Food

Harvard scientists have developed a coating to stop biofilms forming in food processing machines and surfaces by tricking bacteria into thinking there is nowhere for it to attach and grow.

In a study undertaken by co-authors Joanna Aizenberg, Alexander Epstein and Tak-Sig Wong, solid surfaces were covered with an immobilised liquid firm so bacteria cannot grip and grow together into biofilms.

Known as Slippery-Liquid-Infused Porous Surfaces (SLIPS), the technology creates a hybrid surface that is smooth and slippery due to its liquid layer.

Aizenberg, Amy Smith Berylson Professor of Materials Science a 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.

She added: “The fluid forms a smooth, flat lubricating layer over the whole surface, and remains stably attached by adhering to the pores. 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”.

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 sanitising methods and become constant sources of contamination, resulting in lowered shelf-life of products and potential consumer illness.

Aizenberg also said that there are a number of methods to apply SLIPS on to industrial metals, such as aluminium, which is commonly used for machinery and surfaces in food processing and packaging facilities.

She said 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 research team examined chemical coatings, antibiotics and textured surfaces have all been used to try and deter biofilm build up.

She continued: “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).

“As a result, conventional solid-state anti-biofouling materials are non-ideal in preventing long-term biofouling”.

The research team have shown that SLIPS prevents 99.6% of Paseudomonas aeruginosa biofilm attachment over seven days, as well as Staphylococcus aureus (97.2%) and Escherichia coli (96%), under both static and physiologically realistic flow conditions.

Aizenberg said: “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”.

For future studies, the research team 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.

Aizenberg said: “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 optimising our SLIPS fabrication processes, and we expect to see some SLIPS-related products for specific applications fairly soon”.

She also said that they hope 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.

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