It’s no secret that the natural world informs the technological sphere a great deal, and Linköping University’s (LiU) sensor technology—inspired by the very intricacies of human skin—is no exception.
Developed by LiU’s Laboratory of Organic Electronics (LOE) division, the polymer-based technology reflects real-life sensing inasmuch as our own skin carries electric pulses, including pyroelectric (i.e. electrically-charged when heated) signals and properties.
The implications of such natural, intuitive sensing carry plenty of potential. Magnus Jonsson, who leads the LOE’s Organic Photonics and Nano-Optics group—an 8-person research team focused on both sensing and energy harvesting concepts—believes the potential applications include such milestones as touch-sensitive prostheses and self-powering robotics.
Magnus Jonsson, associate professor of the Laboratory of Organic Electronics at Linköping University.
LiU prides itself in providing “world-leading, boundary-crossing research in fields including materials science”, of which the LOE’s skin-inspired technology is a shining example. In this interview, Magnus discusses the inner-workings of the sensor, the university collaboration involved, and much more.
Sam Holland: Let’s start with an introduction of yourself and a little bit about LiU’s Laboratory of Organic Electronics division.
Magnus Jonsson: As you mention, I’m an associate professor at the Laboratory of Organic Electronics (LOE) at LiU. I lead a group called Organic Photonics and Nano-optics. At the moment there are 8 people in our team, including myself—altogether the team consists of PhD students, postdocs, and me.
We are working with nano-structures for different types of applications: while these obviously may involve sensors, such as the ones in the study that we’ll be talking about, nano-structures can also be used in other types of applications and in fundamental studies.
As touched on, my group is part of a larger division called LOE, and it comprises around 100 researchers in total. As with quite a lot of the research that we do, this study was also a part of a collaboration with several of the other teams in the division.
To cover a little more about me, I've been here at LiU in Sweden for about 5 years. Before that, I was a postdoctoral researcher in the Netherlands at Delft University of Technology, at the Bionanoscience department at the Kavli Institute of Nanoscience.
My PhD is from Chalmers University of Technology in Sweden, and when I was an undergraduate I studied at Lund University. So I've been moving around a bit. As mentioned, I've now been here at LiU for quite some time, building my research group.
SH: Could you walk me through the skin-inspired sensor and how it works?
MJ: I'd love to do that: the sensor is inspired by natural skin, in the way that it involves ionic and electronic interactions. And also in the way that it utilises pyroelectric signals and properties, which is actually something that you find in many biomaterials—such as, again, skin.
The technology works with 2 combined concepts: 1 is pyroelectric sensing, i.e. a technique that can measure changes in temperature. If we go from hot to cold, it will give a signal. But the signal will not remain at the new equilibrium temperature. So it's a transient signal that comes from the change in temperature.
The second part of the device is based on the concept of thermoelectrics. The thermoelectric signal arises from a difference in temperature between the 2 sides of the device. So you heat one side up—for example, at body temperature—and it induces a change in temperature between the bottom and top side. And this induces a signal: a thermoelectric potential, which provides a response at equilibrium.
We have also added a so-called plasmonic structure in the device, or a nano-optical metasurface. There are many names for these types of surfaces, but the main function is that they enhance the light absorption of the device, which, in turn, is converted into heat. This also makes the device able to sense light irradiation.
We used this to detect simulated solar light; but in principle, one could also control the sensitivity to different wavelengths of interest to, for example, monitor ultraviolet exposure or whichever type of light irradiation is sought. I’d say that light sensitivity is the second functionality of the device. The third one, which is also related to heat, is its touch detection.
SH: What is the main challenge that you have come across when developing the skin-inspired sensor? And how did you overcome that challenge?
MJ: I’d say that the prime challenges have been practical. For example, it has been a challenge to create a complete stack of layers without encountering any unwanted contact through the layers, because that leads to short circuits.
Thankfully, the PhD student and the first author of the study, Mina Shiran Chaharsoughi, solved that issue by improving the fabrication protocol, so that the yield of working devices improved greatly. I would like to highlight the students’ important roles in our projects and Mina really did the large part of the work, together with the other co-authors.
SH: Absolutely—and talking of student recognition, could you describe the roles that some of the team members have been playing in the sensor project?
MJ: As mentioned, PhD student Mina Shiran Chaharsoughi has done a lot of the experimental work—which has been carried out with the help of Dan Zhao, who is one of the three corresponding authors on the study. She is an assistant professor—both when it comes to experiments as well as in guiding the research. She has a strong background in heat sensing.
So has Xavier Crispin, who is a professor at the LOE who has also been involved in the project, and an expert on organic thermoelectrics.
And then we have associate professor Simone Fabiano, who’s also a corresponding author of the study. Together with Dan Zhao and others, he has been developing some of the materials and concepts that we used in the study. So that was important also.
And then there’s me. My own background is primarily in the optics side, and I've been leading the study. So it's really a collaboration between people in both my own group and other groups in our research environment. That is often how we work here at the LOE.
The combined concept, ultimately, entails several different concepts, physics phenomena and chemistry. So it has very much benefited the project to have several people involved with such a variety of backgrounds and expertise.
SH: I'm just going to quote LiU's news piece regarding the technology now: “Robotics, prostheses that react to touch, and health monitoring are 3 fields in which scientists globally are working to develop electronic skin.” Which of these 3 applications (or otherwise any other applications) do you consider the most suited to the sensor technology—and why?
MJ: It's a somewhat challenging question, because you have to pick a favourite! But perhaps it could be robotics. And that’s particularly in regards to robots mimicking humans: picture humanoids that are made to have the same type of sensations that we have. In other words, consider artificial skins for robots, which can measure changes in temperature, including environment temperature and their own temperature, as well as light exposure and warm touch.
So that is something that we believe could be quite suitable for the technology. And regarding prostheses, while the technology doesn't address things like how to control limbs or anything like that, it could help to provide sensation to prostheses also—just as it could provide sensation to robotics.
The intention is not really to create real skin, but more to provide the same type of functions that real skin has. And one day, in fact, why not provide more functions still? But that’s another story for another time.
SH: Off the back of that last point, are there limitations of human skin that you wouldn't want to have—in other words, are there any things that could be added to make artificial skin even better than its model?
MJ: Yes, I think so. It could be useful if the artificial skin would be, for example, able to distinguish between exposure to different types of irradiation. But this is not something that we have explored yet. But potentially one could implement wavelength-dependent sensor signals via the plasmonic metasurfaces of our sensors.
SH: If the technology were to become more widespread, in what ways do you think the medical world would especially benefit from it?
MJ: That's a good question. I didn't mention health monitoring before, but that's indeed also an interesting application. And we see it as having the potential to apply to something like an adhesive bandage, like a Band-Aid. Something like this could monitor body temperature. And while you could do this with other relevant techniques, too, our system provides particularly rapid signals.
The situations where this could be beneficial could be, for example, in extreme environments, like that for firefighters, or maybe in space, or for people working in mines—altogether situations and places where you want to be able to quickly measure temperature changes so you can respond if something's wrong.
Such sensor technology could also relate to monitoring exposure to different types of light irradiation. While we didn't do so in the study, the devices could also be designed to be flexible, which would form devices that could be quite easily attached to people’s bodies. And the type of materials that we use could be, we believe, printed in the future, and/or quite easily scaled up to larger systems.
And this would also be at quite low costs, alongside the said advantages of scalability, too. Given the said features, the technology could hopefully benefit existing and future medical applications.
SH: You mentioned the potential for printing the materials—what type of printing systems do you think would apply?
MJ: We work primarily with printing techniques like screen printing and ink-jet printing, which can be used to make layers, like printed electronics.
You could think of doing 3D-printed devices too, but this is not something that we have tested for these devices.
SH: While you have already touched on this, is there any other ways in particular that you see the robotics industry benefiting from the technology?
MJ: We hope so. It could be a new type of technology that enables the sensation of heat and irradiation, as well as touch. We believe that there is a need for such improved sensors for use in the robotics industry. It's also important that they consume as little power as possible, and the whole concept itself is in fact self-powered.
This is another one of the major advantages and reasons why we studied this type of concept: the signals arise due to the sensation itself. What I mean is that we don't have to apply an external voltage and induce an electric current through the device, like when measuring changes in resistance. Instead, the signal arises on it's own, so it's self-powered. And given this feature, this is something that we believe could benefit all manner of applications, but not least robotic systems that would benefit from miniaturised batteries and low power consumption.
As mentioned earlier, perhaps the sensor’s most interesting potential, I think, is in regards to robots mimicking humans: the idea of humanoids is where we could have the strongest impact.
It's hard to know who’ll pick it up. But we hope many will.
SH: What are your overall plans and hopes for the technology in the future?
MJ: That's an important question. Again, we hope that other people appreciate the study and that it inspires researchers as well as innovators to continue to explore such devices and sensors. An interesting aspect is that the heat and light sensor is based on a combination of ionic and electronic interaction, and we are now investigating new types of related concepts. We are also interested in continuing to improve our sensors—for instance, with respect to making them flexible.
A huge thanks to Magnus Jonsson for providing a view into Linköping University’s ground-breaking research, which can you read more about on LiU's news site and in Wiley Online Library.
The scalability involved in the Laboratory of Organic Electronics’ skin-inspired sensor could mean revolutionary advancements for a wide range of applications in several areas, from the medical field to robotics and emergency response. We look forward to seeing what the future has in store.
To read more about university research into novel approaches to sensing technology, why not read Electronics Point's product piece on MIT's radiofrequency solution to machine vision.