Ep. 80: What progress has been made in flexible electrodes? Ankit Podcast

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Ep. 80: What progress has been made in flexible electrodes?

To kick off 2022, Victoria Nickerson interviews Milon Hossein, a graduate research assistant at North Carolina State University (NC State) in the US.

Speaker 1: WTiN
Speaker 2: Milon Hossein

Speaker 1
Hello, my name is Jessica Owen, and I'm part of the team here at WTiN. And this is the WTiN podcast. Join me, my colleagues and our guests every month, as we talk about new and interesting innovations from across the textile and apparel industry. Whether it's talking to sustainable startups quizzing experts on the latest research and development, or chatting to companies about their most recent products, you can rest assured that the WTiN podcast will connect you with everything you need to know. For the first episode of 2022, my colleague Victoria Nickerson is joined by Milon Hossein, a graduate research assistant at North Carolina State University. They chat about what progress has been made in flexible electrodes for wearable textiles and the remaining challenges in terms of developing and commercialising these technologies.

Thank you for joining me, Milan, how are you today?

Speaker 2
Yeah, I'm good. Thank you for the opportunity. 

Speaker 1
No worries. So I guess before we sort of get stuck in to the research, could you tell me a little bit of background about the project, sort of what flexible electrodes are and why they're important for smart textiles

Speaker 2
Alright, so, the project is like developing comfortable not only flexible, but also comfortable a child who is is most of the time in with their skin contact. So, a particular focus on textile, due to their excellent skin friendliness. That's why we tried to deep dive in finding the progress in this area and like mapping the progress in different kinds of materials and different structure used to develop the progress in flexible electrode. So, you know, like there are a lot of wearable electronics out there, most of them are like a electronic device, but they're huge progress in developing a very highly flexible and bendable and assessable electrodes using textile materials. And especially in the last decade, this flexible electrodes are striving for skin mounting and like some kind of tattoo based electronics. So, with this thing, different kinds of research is being carried out like there are different fabrication methods Mr step at the time. So, we just tried to summarise all the work is going on in different parts of the world and see like what are the progress and how the technology is moving forward. So I guess.

Speaker 1
What factors have influenced the electrical behaviour of flexible electrodes?

Speaker 2
When we talk about the flexible electrode, there are different kinds of materials, especially for flexibility, like there are some thin film and plastic and besides textile materials, but you know, like the thin film or plastic it's most of the time they are not breathable, like when they're in on the skin for a long time, then it blocks the sweat and causes discomfort that So, textile are more advantageous Yes, in this regard. So, textiles are heterogeneous and very wrapped. So, it's difficult to impart different kinds of electrical functionality because the especially the textile materials are not electrically conductive, they are insulator. So, different kinds of looked at polymers are different match metal nanoparticles are used to impart the electrical functionality to make it electrically conductive. So, the variation in the textile surface chemistry like the origin of the fibre like whether it is coming from an animal or coming from plant dictates the dictates their electrical conductivity and or addition with daily protective polymer. So, you need to consider number of parameters to obtain a better electrical behaviour and some key factors are that the thickness of conductive layers the amount of met conductive materials are being used and the textile geometry like quiz kind of structure used as substrate materials. And as I mentioned, like the type of text materials whether it's coming from natural source or it's a synthetic materials like the polyester and cotton, they have different adhesion with different kinds of materials and the nature of electroactive materials being deposited on the textile surfaces. So, these are all most of the time interrelated and they need to be optimised for better electrical conductivity and durability. At the same time, this conductive textile structure are required to withstand mechanical stresses during manufacturing and during that uses, because the materials are developed it goes through different kinds of handling process and create some mechanical stresses and it should be like strong enough to withstand this kind of forces, there is another crucial requirement like their sustainability in different environment, like a lot of focus is on developing a highly conductive electrode electrode materials. But with time it was found that if the materials is not sustainable in different environment, for example, during washing, then it's problematic because when we're saying textile base directed, we expect that to be used as a regular materials. And if that's not the case, then it's really hard, it's difficult for this technology to commercialise and being used extensively.

Speaker 1
Yeah, I mean, in that you sort of touched on different textile structures are there some that are better for use for flexible electrodes

Speaker 2
Yes, like a two common structure used for flexible electrode one is one dimensional that is fibre or thread, and another is different kinds of fabric. So, it depends like the fibre has less surface area fibres high surface area, but it cannot cover large area application. So, they are mostly used as interconnect materials like connecting to devices or like lawyer, but on the other hand fabric can be used for a large area application like covering a large part of the body. So, these two structure are used depending on the requirement and depending on the applications. So, if I if private is used then the fibre is very lightweight and it can be used in a way used in a very complicated shape. And there are some work going on developing the functionality on the fibre materials. But for example a super capacitor or antenna but integrating electro active materials from the fibre surface is complicated than its counterpart the 2d fabric materials because the fibre surface is very small and depositing different materials uniformly on the fibre is really challenging. But on the other hand, the fabric like oven and knitted fabric structure, they are more easier to be functionalized with conductive materials and they're they're used for different kinds of sensing electromagnetic shielding or thermotherapy etc. Okay,

Speaker 1
I guess in terms of materials, then what ones are being used for flexible electrodes and are there ones that sort of exhibit better electromechanical performance and stability for smart textiles.

Speaker 2
So, like, as as I mentioned, like there are different kinds of materials and some materials are recently developed and they are being explored as well. So, in in a broader sense, like the materials are grouped together like for example, intrinsically conductive polymers. So, this polymers are highly conductive and they can be used in roll to roll manufacturing. So, and any other conventional manufacturing process like coating or printing and some example are like polyaniline polypyrrole, or most popularly used polyethylene dioxins Hi offene alternatively known as p.so These are group up conjugated polymer, but besides this there are different kinds of nanoparticle from different types of metal for example, silver, gold, copper Hmm and also their nanowires. So, they are deposited on textile materials using different kinds of advanced deposition technique they can be coated as well. So, the problem with this materials like especially the gold or copper like they have a different processing method than the textile manufacturing process. So, if you want to think like the cost and the long term application, anyone you don't want to add cost during the manufacturing process, you want to use the existing process. So, beside this different kinds of carbonaceous materials like carbon, black, graphene, Carbon Nanotube and metal carbide or nitride, also known as Maxine, they're like, it's a new material developed in the last decade. So, they are being extensively used these days, because some of them has very good compatibility with texture materials, besides their excellent electrical conductivity. So, all depends on like, their preparation process and the structure of the substrate. So, these are used based on the requirement there in application. 

Speaker 1
So, you mentioned a few interesting materials there, especially sort of Maxine's and graphene. So, do you are these currently being used sort of commercially to produce flexible electrodes between Maxine and graphene

Speaker 2
I think graphene is like pretty Messier materials compared to Maxine, because Maxine has developed this class ticket, but, you know, graphene is was in the market for a while and different scalable manufacturing processes developed. So, I'd say Maxine, already sorry, graphene was already explored in different kinds of application. So, the both of them has some of their unique characteristics. For example, the electromechanical performance of the materials, but it depends on the user case scenario. But in general, like using highly conductive materials produce highly conductive electrode, it's a very common rules. So, if the electrode are used only as interconnects and does not require further hand handling, then it's better to choose the best conductive materials. So, Maxine has different kinds of variations like you can tune their chemical structure and as a result their electrical conductivity changes. So, if you want to make a highly conductive interconnect, maybe you can use Maxene or you may use some hybrid materials like combining both or sometimes some metal nanoparticles are also added to increase their electrical conductivity. But if the electrode are required further processing and subjected to environmental condition, then it is it is very critical to choose appropriate materials because some materials shows very high electrical conductivity, but their adhesion and their bonding with the textile Mattea textile substrate might not be strong. So, when it comes in contact with like soil or water, then it may the the performance may degrade and sometimes during washing it completely be gone. So, you want to be actually very careful, depending on the as, as I mentioned, like the application dictates the material choice, like most of the conductive materials show some conductivity with the textures. But where do you want to use it and how you want to use it that defines, like what kind of materials is more suitable. So, for example, like, if you're, if you're making a garments using a conductive material, say graphene or Maxene, then it should be able to raise the twisting, stressing and bending, which is a very common process. But if the coating is very steep on the surface, and it's loosely attached to the materials, then during this process, some materials will be fall off from the surface and at the end, you'll have poor performance after some times. So I had not say like with graphene or Maxine, like perform better than other but I would say, depending on the user case scenario You're you have to be very clever to use the materials and apply them on the textile substrate. And then you can optimise the performance and get better functionality out of this.

Speaker 1
So another sort of factor that comes into play, I guess, is sustainability, because that's quite a big topic for the smart textiles industry. So when you're sort of thinking about that, are there any materials that are maybe better to use, they're a bit more sustainable than others.

Speaker 2
So like as using P dot PFS, and some graphene and Maxine. So a big part of this materials like using these materials, like how long the materials can sustain, and how long their performance is intact, like is not degraded over time. So I see like, the graphene has very good, very good addition to the natural fibre, natural textile, especially cotton. But when you want to use that with some other synthetic materials, maybe you need to do some surface modification or some cross linking. And same goes for the vaccine, like Maxine has direct reactivity with the cotton because there's chemical structure. But the problem is like, if you don't use any binder, then it will, it will go it we'll be gone. So, you need to find appropriate binders, so that it stick with the materials and you get better performance out of this. So it's same for the PEDOT PSs like that is another popular chemical use for flexible electoral, especially textiles. So, like some process shows that it is stable and sustainable for maybe five or 10 washing, but when a binder is used that can be extended up to 40 to 50 Washing cycles. So that similarly, like it goes for all other processes like mechanical performance, so the better the reactivity and better the bonding between the substrate and active materials, it will be very stable, and it can be more sustainable.

Speaker 1
So in terms of application areas, what are flexible electrodes being used in at the moment.

Speaker 2
So the application actually is very wide, like hundreds of application being explored. So but if you want to be specific, then I would say sports and healthcare are the dominant for the flexible electorate, because this market is pretty Hughes. So most of the commercial focus, like different kinds of companies are focusing mainly on developing some flexible electrode materials for application in sports rehabilitation, or healthcare monitoring. And yeah, there are some other application like it could be used in thermal therapy or electromagnetic shielding. So different folks, and some other new application like sailboard sensor, they're emerging over time. 

Speaker 1
So I guess, to sort of finish off with them, what challenges still exist, I guess, for the development and commercialization of this kind of technology.

Speaker 2
So the challenges are actually multifaceted. Like they're like in the market, there are already some product for example, hexo skin and Maya and the two major companies who are developing smart shard or undergarments to commercially monitor the biophysical data such as ECC, or heartrate. So the problem is like, these are the these are the company they're using some conductive materials and using some kind of textile palm to monitor this data, but this data is personable in some insane in a sense, like if they're usable for clinical setting, like if they're reliable for clinical diagnosis. So still, there are a lot of works going on and improvement is going on to see like how reliable this data especially when it comes about the buyer potential or different camps kinds of health information, but for the entertainment and communication, you see it's in advance. Like some is much hard for music and some some other human machine interaction, so they're just coming up and advancement are going on. But, you know, as I mentioned, reliability and their clinical approval is very important. But besides this, the stability, like, as I discussed, like their environmental stability or their mechanical stability is very critical. And the most of the time, the performance of the materials degrades over time. So it's important to make sure that the performance from the development and until the lifecycle of the product is similar. So it's very important to maintain that. And another issue is the cost lies, which is a big barrier for the development of this few like compared to a regular t shirt, a smart t shirt could cost three to 20 times. So with the big challenge, and technologically there is another challenge like device compatibility, so when we're talking about a flexible electrode, but we want to interface that with some other devices, for example, data transfer or power powering these devices, so that their progress on like the flexible electrodes developed significantly compared to those devices, especially power transferring, powering these devices or data transferring, because there is not enough progress in powering these devices like the power devices are mostly reserved. So, if you're connecting the flexible electrode with rigid power sources or a data transfer devices, then the goal of textile based devices or skin friendly device is not met like you have a rigid power system and the other is it device to transfer the data, but it will just have a flexible electorate. So this is a huge mismatch between this between the technology. So I think huge improvement and research is required to develop a highly flexible power sources and data transmission devices. And then in the importance and practical application of this field will be realised completely. And I think that would be more commercially successful. Thanks.

Speaker 1
I mean, it sounds like there's been a lot of interesting progress for flexible textile electrodes. So thank you very much for chatting with me today and letting us know about more about your research.

Speaker 2
Thank you, chill. I had the chance to share that and yeah, definitely. It's interesting field and hope. And next decade, we'll see a lot of progress.