Mosquito-repelling socks

18 September 2018

Interview with 

Dr Mthokozisi Sibanda, University of Pretoria

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Here’s a story about something that you’re definitely not going to see on the catwalk at London Fashion Week (it’s something highly practical for a change): socks that could save you from mosquito bites and also malaria. Chris Smith spoke with Mthokozisi Sibanda from the University of Pretoria.

Mthokozisi - My name is Dr Mthokozisi Sibanda. I’m from the University of Pretoria.

When you’re outdoors mosquitoes will bite you on the ankles and feet 93 percent of the time. They are attracted by foot odour.

Chris - Isn’t that where we spray the insect repellent then?

Mthokozisi - Yes. You can spray topical insect repellent but it will quickly evaporate - in an hour or two it’s no longer effective, then you have to respray again. So we needed to come up with a way of having a long lasting formulation, so basically what we developed is a slow release technology. We spin a fibre and the fibre is specially engineered to hold a liquid insect repellent and the fibre will slowly release that repellent over a long period of time. It can last up to eight months or if you knit the fibre into a textile you can wash that textile for a minimum 25 times and it’s still effective.

Chris - So you would put the formulation into this fibre using the technology you’ve invented and what, you then spin it into a pair of socks or an anklet or something that a person would wear?

Mthokozisi - That’s correct.

Chris - Does it work?

Mthokozisi - It works. We have tested it; we have actually published the results in a high impact scientific journal.

Chris - How effective is it and how did you do that testing?

Mthokozisi - Okay. There are a number of tests recommended by the World Health Organisation. The one that we use is a pretty agressive one where we put our formulated sock on one foot and a control sock, which is untreated, on the other foot. We put both feet in a cage with 300 female hungry mosquitoes. They have to make a choice: which ankle do they feed on. If you see all of them going to the untreated sock then you know that your sock is working.

Chris - That sounds like a really painful experiment. Did you do it?

Mthokozisi - I did it. But you know you have people who run these insectories and they use their arms to feed the mosquitoes. So what I did is really nothing to what other people do.

Chris - Things that people will do for science! But tell me about the technology that’s enabled you to do this? How does this clever fibre and fibre spinning technique work and how do you get the insect repellent in there in the first place?

Mthokozisi - What we make is what we call a bi-component fibre. One polymer is in the core and that polymer can absorb a high amount of oil. And we have a polymer that forms a shield around the core polymer so the oil will have to diffuse through that shield. In that way, the shield slows down the evaporation of the oil overall. If you knit the fibre into a textile and wash that textile, you only wash the outside of the fibre, the bulk of the liquid is still stored inside the fibre. It will still migrate to the surface and that’s how it’s replenished.

Chris - In essence, it’s a tube within a tube. And the tube inside the tube loves oily things, the tube outside the tube hates oily things. So you’ve got your repellent which is oily based in the middle and it’s obviously facing a barrier to diffuse out very slowly. What is the chemical that you’re using as the repellent - is that just DEET or something? Because that’s the industry leading standard DEET, isn’t it?

Mthokozisi - Yes. DEET is the standard repellent on the market right now. It’s got a bad reputation, unfortunately, although it has not been proven to be bad scientifically. So we are using an alternative repellent called IR3535 - it’s as good as Deet. We also use a natural repellent based on the eucalyptus tree.

Chris - Are these socks or whatever you design fashionable because obviously, especially with youngsters, people are not going to wear something that looks like a fashion disaster? So can you add colour, add patterning; make it like it’s a normal piece of everyday wear so it doesn’t look out of place?

Mthokozisi - Yeah. When it comes to that it is so easy because we can make the fibre into any colour - we just add a pigment. We can make any sock design. We actually combine our yarn with the liquid, with cotton wool to make it nice and comfortable and you can make a nice fashionable sock.

Chris - How will I know though when my socks are no longer working? Because it’s brilliant while it is working of, course, but there has to be a way of knowing when I’m no longer protected because otherwise I could be out there with false confidence and catch something.

Mthokozisi - Basically, we do lab testing to determine the length that these products can work, and we can sort of calculate the minimum length that you should keep them for. So they will be labeled to say they can work for this long and after this it’s recommended that you get a new product.

Chris - Can you recharge them or do you have to throw them away because, obviously, that’s not great from a sustainability point of view?

Mthokozisi - No, you’re right. You can’t recharge them and what we are doing right now is we are developing the fibre based on biodegradable polymer. There is research that is ongoing to use biodegradable polymer so that they can be disposable.

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