A new self sterilising plastic

The spread of infections in healthcare settings is a major problem. Dirty hands are one source, but equally, surfaces like gloves and aprons, and other single-use plastics can also pick-up and pass-on bacteria and viruses through contact. As he explains to Chris Smith, Andrew Mills, from Queen’s University Belfast, had the bright idea of adding something to plastic that reacts with light to produce a bleach-like substance on the surface that can wipe out contaminating microbes…

Andrew - I knew that there was an awful lot of disposable plastic materials that were used in the healthcare industry that provided a clean surface, but rapidly got contaminated. And of course, I also knew that one of the major ways that viruses and bacteria are transmitted in a healthcare environment is by landing on the surface. And then you touch that surface. So I wanted to imbue these plastic disposable materials with extra value, and that value will be the ability to self sterilize.

Chris - How?

Andrew - It's really neat. You can put pigment particles into them, really inexpensive. They are basic pigment particles used in paint, it's titanium dioxide, but in paint, they actually coat the pigment particles so that they don't actually do any photochemistry. That means they don't interact with light and then generate things on their surface that would do damage to the polymer because you don't want your paint falling off. But here we do. We want those pigment particles to actually absorb light and then destroy anything that's on its surface. So that's what we do. We use naked titanium dioxide particles, put them into plastic and they're able to destroy viruses and bacteria in particularly, most notable these days SARS-CoV- 2

Chris - Something similar has been done with self cleaning glass. Hasn't it? I think King's Cross station in London was one of the first places to do this where by adding dioxide particles to the glass, it then reacts with the ambient light to produce nasties that blitz the dirt. So you basically endowed a plastic bag with what they did at Kings cross.

Andrew - Exactly.

Chris - The difference is that at King's Cross station, the sunlight shines hopefully some of the year on the glass. Your plastics, if they're in a clinical setting, as you're advocating for, they're gonna have just artificial light. Is there enough energy in that light to make this work?

Andrew - That's a really good point. The interesting thing about these pigments is they really don't need very much to make them quite reactive and certainly reactive enough to generate the small level of bleach, which is effectively what it does on the surface to destroy a virus or a bacterium. You only need to damage them before they die. So the question is, is there enough? And the answer is, yeah, there's window light. And there's a bit of UV light that comes in there. But also a lot of fluorescent tubes, well all fluorescent tubes, actually emit a small amount of UV. And so when we were doing our trials, we were using room light, fluorescent lamps and very low UV light associated with that coming through windows. One of the things that really surprised us was both worked, but actually the room light one worked really well. We thought it was going to be so small because there really is like a micro watts centimeter squared of UV falling onto the surfaces, but actually they seem to use them very well. And then it was sufficient to destroy the kind of levels of bacteria and viruses that we were looking at.

Chris - The chemistry that's going on then? The UV light that's coming from, whatever source hits this titanium dioxide, how does it then turn into, you dubbed it bleach? What does it do when it hits the titanium dioxide to then produce something capable of destroying microorganisms?

Andrew - So when you shine light onto these pigment particles, you create bleach light molecules that can destroy viruses and bacteria.

Chris - And what sorts of microorganisms will they knock out in your plastics?

Andrew - We tried it with SARS- CoV-2 and it worked very well for them. And also the influenza virus. We looked at some other viruses as well. It actually worked for all of them.

Chris - Can you turn the plastic into a range of different things? Is it actually plastic that you could use the same way? We love using plastics, can you turn it into any kind of shape, size or characteristic within reason?

Andrew - You can and a lot of people have used the same technology to create things like mobile phone covers and keyboards for computers. We are not so much in favor of that because once you start handling it, you put on sufficient coating of all the sweat and the grease and whatever it is that you've got in your fingers, the then it overwhelms the ability of this material to keep itself clean, disposable plastic materials, where you are worried about the micro droplets that are coming from your breath, falling on it and then transmitting those viruses or bacteria to some other person. This is what this technology is targeting.

Chris - Is it easy to do Andrew? To make this? Because obviously one of the big attractions of plastics and one of the reasons it's such a scourge now is because it's really cheap. So does this enormously increase the cost burden of making these things? Or is it very easy to do?

Andrew - I'm sorry, I interrupt you because of my enthusiasm for it. We use extrusion to make these, there's nothing special about this. You just, when you're making this thing, instead of adding one pigment, you add our photo-active pigment. That's the only difference. And the photo-active pigment pigment is that used or behind it is that used in paint. So it's incredibly inexpensive. It will not add any great cost to a penny. Maybe, even less than that, to what the existing cost of that apron or that tablecloth or that curtain is at present. The beauty of this is that it has this extra value, this extra ability to keep you safe and well.