Modifying polyethylene for the production of antimicrobial surfaces

Ari – Year 12 Student

Editor’s Note: Aspiring chemical engineer Ari in Year 12 writes here for the GSAL Science Magazine about how polyethylene might be modified in such a way as to allow it to be used to produce anti-microbial surfaces. This is Ari’s third contribution to The GSAL Journal; you can read more from Ari here. CPD

Modifying polyethylene for the production of antimicrobial surfaces

Sanitation and hygiene are fundamental principles for survival in this chaotic year: hand sanitiser prices have risen by 255% since February[1], the industry warns for a face mask shortage[2], and there’s about nine highly concentrated methanol sanitisers out in the market which can cause blindness and death.[3] While not for our direct use, antimicrobials still form part of the sanitation procedures that are taking place now. Surface antimicrobials are used extensively in hospitals, operating rooms and more: with this use and overuse of antimicrobials, resistance has arisen.

First, I think it’s important to clear up how bacteria are required for our survival, in the end, they’re inevitable. Roughly, the average 70kg man has 3.8×10^13 bacteria in their bodies.[4]However−there are also dangerous bacteria. To combat such, we use antimicrobials, which are defined as substances that are “able to destroy harmful microbes (in other terms, small living things that can cause disease)”[5] Antimicrobial resistance is a battle that has concerned the scientific world for a while. The WHO has highlighted this issue in the past, next to the antibiotic resistance crisis.[6]

About a week ago or so, I had the chance to attend a webinar presented by the Institute of Molecular Science and Engineering (IMSE)[7] from Imperial College London where Professor Daryl Williams, from the faculty of chemical engineering, explains their progress and development of low cost polymer materials that will contribute to making more progress towards tackling this antimicrobial resistance.

The research conducted focused on pseudomonas aeruginosa, whose derivatives are the cause of infections in varied parts of the body after surgery[8]. What makes these bacteria more concerning is the higher risk carried for people with medical conditions with weaker immune systems, and its resistance to chemotherapy drugs and some antibiotics, making it a hard-to-kill bug.

Polyethylene, known to be the most common polymer – dominating as much as 34% of the plastics market[9] – is used in bottles, packaging films and practically almost every container of any drink or food[10]. This is mainly due to how inert and low absorbent they are, as well as their hydrophobic properties (meaning they despise water deeply). This becomes a double-edge sword; its hydrophobic properties are compatible with bacteria, making it essentially its dream surface.

The process that involves modifying ethylene involves surface chemical etching and oxidation, which requires high pressure. Acid etching is already a widely used method for modifying other polymers; it is low cost and uses an acid such as chromic acid. By improving the adhesion properties of the polymers, they can be coated with a desired material, or simply leaving them to be printed to bond it with other materials.[11] The reaction mechanism that they suggested is highlighted below:

[12]

What makes this process so practical, as professor comments, it’s the simplicity and quickness of it, as it allows for the introduction of oxygen-containing groups to the surface of the polymer. However, this is still in the development stage, as its antimicrobial properties haven’t been tested entirely.

The procedure they used to research involved exposing the sample of the polymeric material to a solution with bacteria for 30 minutes, and then rinse the planktonic bacteria from it. What then followed involved dying the sample with a fluorescent substance, which serves to stain the DNA of the bacteria, to then be later visualised using confocal microscopy (a specific type of microscopy technique, used in particular to visualise details in cells[13])

The results of the research showed the high potential the process has despite being so simple. The initial biofilm attachment of the bacteria was significantly lower after the antimicrobial was used, showing how something as basic such as oxidation dramatically reduces the concentration of bacteria attached to the surface. The concept is not new, as other oxidised substances such as wine also have antimicrobial properties, but it presents a new and exciting way to effectively mass produce safer polymers.[14]

What was impressive, was how effective it was when reducing the concentration of other bacteria they tested it with, including staphylococcus aureus and Escherichia coli (E coli is responsible for food poisoning and other diseases[15]), still working in a similar way as it did with the pseudomonas aeruginosa.

Given my interest in nanotechnology processes too, I questioned professor on the possibility of using alternative methods to modify the polymer, such as nanolithography, (a process that involves imprinting, writing or etching patterns at the nano scale to create incredibly small structures[16]). Although this is indeed a much more thrilling process, he clearly pointed out how the main focus on their research lies in making it affordable and viable, as he states they need to be low cost so that they might be extensively available. This left me with a further interest to research on the possibilities that nanotechnology could offer, perhaps in a future where they become more economically viable, which I will intend to read further on.

There was also a suggestion of the possible uses of antimicrobial polymers for the treatment of water to kill microorganisms, which in theory polyethylene could work for, as he expressed. However, there is additional research being carried on now too, which focuses specifically on the treatment of water, targeted on the bacteria that predominantly live in there.

Overall, Williams emphasised how the surface properties of polyethylene with metal oxide nanoparticles are an under-researched topic, and he left a clear message that further work needs to be done, as this way it reduces antimicrobial resistance. In addition, his message conveyed a hope to see if the manufacture of these new materials can be beneficial for hospitals and operating rooms and finally make it into a real-world application.

The more subtle lesson from this webinar also, I believe, is its emphasis on the dependence of plastics in the modern world. While being necessary for now while new materials are developed, plastics are far from being ideal. 300 million tons of plastic every year are mass-produced, being half of them single use plastics[17]. In the meantime, while our dependence on them cannot be fixed, there is at least work being done to make them more useful.

Ari 902669

[1] https://news.sky.com/story/coronavirus-rise-in-demand-for-hand-sanitisers-and-hygiene-products-11948021 (25/6/20)

[2] https://www.ft.com/content/f726a253-664f-406f-8daf-6b313c0cf8e4 (25/6/20)

[3] https://www.independent.co.uk/news/hand-sanitiser-toxic-fda-warning-methanol-poisoning-eskbiochem-sa-de-cv-a9579816.html (25/6/20)

[4] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4991899/ (25/6/20)

[5] https://dictionary.cambridge.org/dictionary/english/antimicrobial (25/6/20)

[6] https://www.who.int/features/qa/75/en/ (25/6/20)

[7] https://www.imperial.ac.uk/molecular-science-engineering/ (25/6/20)

[8] https://www.cdc.gov/hai/organisms/pseudomonas.html (25/6/20)

[9] https://www.plasticseurope.org/application/files/5715/1717/4180/Plastics_the_facts_2017_FINAL_for_website_one_page.pdf (25/6/20)

[10] https://www.britannica.com/science/ethylene (25/6/20)

[11] https://www.masteretching.com/chemical-etching-process#:~:text=Chemical%20etching%20is%20a%20method,to%20create%20the%20desired%20image. (25/6/20)