A sweat-based flexible supercapacitor (SC) for self-powered smart textiles and wearable systems is presented. The developed SC uses sweat as the electrolyte and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as the active electrode. With PEDOT:PSS coated onto cellulose/polyester cloth, the SC shows specific capacitance of 8.94 F g-1 (10 mF cm-2 ) at 1 mV s-1 . With artificial sweat, the energy and power densities of the SC are 1.36 Wh kg-1 and 329.70 W kg-1 , respectively for 1.31 V and its specific capacitance is 5.65 F g-1 . With real human sweat the observed energy and power densities are 0.25 Wh kg-1 , and 30.62 W kg-1 , respectively. The SC performance is evaluated with different volumes of sweat (20, 50, and 100 µL), bending radii (10, 15, 20 mm), charging/discharging stability (4000 cycles), and washability. With successful on-body testing, the first demonstration of the suitability of a sweat-based SC for self-powered cloth-based sensors to monitor sweat salinity is presented. With attractive performance and the use of body fluids, the presented approach is a safe and sustainable route to meet the power requirements in wearable systems.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/adma.201907254

A Wearable Supercapacitor Based on Conductive PEDOT:PSS-Coated Cloth and a Sweat Electrolyte.

There is a growing demand for developing wearable sensors that can non-invasively detect the signs of chronic diseases early on to possibly enable self-health management. Among these the flexible and stretchable electrochemical pH sensors are particularly important as the pH levels influence most chemical and biological reactions in materials, life and environmental sciences. In this review, we discuss the most recent developments in wearable electrochemical potentiometric pH sensors, covering the key topics such as (i) suitability of potentiometric pH sensors in wearable systems; (ii) designs of flexible potentiometric pH sensors, which may vary with target applications; (iii) materials for various components of the sensor such as substrates, reference and sensitive electrode; (iv) applications of flexible potentiometric pH sensors, and (v) the challenges relating to flexible potentiometric pH sensors.

/pdf/flexible-potentiometric-ph-sensors-for-wearable-systems-43twl1k77q.pdf

Flexible potentiometric pH sensors for wearable systems

Temperature sensing is an important parameter needed to be measured by the eSkin during the physical interaction of robots with real-world objects. Yet, most of the work on sensors in eSkin has focused on pressure sensing. Here we present a skin conformable printed temperature sensor with poly(3,4-ethylenedioxythiophene): poly (styr-enesulfonate) (PEDOT:PSS)-graphene oxide (GO) as a temperature sensitive layer and silver (Ag) as contact electrodes. The demonstration of PEDOT:PSS/GO as a highly temperature sensitive layer is the distinct feature of the work. The response of presented sensor observed over ~25 °C (room temperature (RT)) to 100°C, by measuring the variation in resistance across the GO/PEDOT:PSS layer showed ~80% decrease in resistance. The sensitivity of the sensor was found to be 1.09% per °C. The sensor’s response was also observed under static and dynamic bending (for 1000 cycles) conditions. The stable and repeatable response of sensor, in both cases, signifies strong adhesion of the layers with negligible delamination or debonding. In comparison to the commercial thermistor, the printed GO/PEDOT:PSS sensor is faster (~73% superior) with response and recovery times of 18 s and 32 s respectively. Finally, the sensor was attached to a robotic hand to allow the robot to act by using temperature feedback.

/pdf/printed-temperature-sensor-based-on-pedot-pss-graphene-oxide-htpkd4j5vb.pdf

Printed Temperature Sensor Based on PEDOT: PSS-Graphene Oxide Composite

Bioinspired transparent and antibacterial electronic skin for sensitive tactile sensing

Inspired by biology, significant advances have been made in the field of electronic skin (eSkin) or tactile skin. Many of these advances have come through mimicking the morphology of human skin and by distributing few touch sensors in an area. However, the complexity of human skin goes beyond mimicking few morphological features or using few sensors. For example, embedded computing (e.g. processing of tactile data at the point of contact) is centric to the human skin as some neuroscience studies show. Likewise, distributed cell or molecular energy is a key feature of human skin. The eSkin with such features, along with distributed and embedded sensors/electronics on soft substrates, is an interesting topic to explore. These features also make eSkin significantly different from conventional computing. For example, unlike conventional centralized computing enabled by miniaturized chips, the eSkin could be seen as a flexible and wearable large area computer with distributed sensors and harmonized energy. This paper discusses these advanced features in eSkin, particularly the distributed sensing harmoniously integrated with energy harvesters, storage devices and distributed computing to read and locally process the tactile sensory data. Rapid advances in neuromorphic hardware, flexible energy generation, energy-conscious electronics, flexible and printed electronics are also discussed. This article is part of the theme issue 'Harmonizing energy-autonomous computing and intelligence'.

https://royalsocietypublishing.org/doi/pdf/10.1098/rsta.2019.0156

Soft eSkin: distributed touch sensing with harmonized energy and computing.

With robots entering our lives in a number of ways, their safe interaction, while operating autonomously, has gained significant attention. We no longer speak of robots as only the industrial tools needed for repetitive tasks such as picking and placing, or robots kept away from people. Not that such tasks are unimportant, it is that significant progresses have been made in these application areas and now the focus is gradually shifting toward robots handling real-world objects under arbitrary circumstances, working safely alongside humans, and assisting them. The physical interaction by touching is important during such tasks to get an estimation of contact parameters (e.g., force, soft contact, hardness, texture, temperature, etc.) and this makes the tactile/touch sensors and haptic feedback critical for robot technology, which is opening up more and more applications [1] This trend will continue as we enter the era of smart factories, Industry 4.0, social robots, telesurgery, and so on, where robots are intended to work closely with human. Robotics is set to become the driving technology underpinning a whole new generation of autonomous devices and cognitive artifacts, providing a link between the digital and physical world. In fact, we are looking at a profound evolution, where artificial intelligent (AI) systems could be extended into robots with new embodiments for applications such as brain-controlled robots and haptic avatars [2] . New automation concepts such as human–robot collaboration (HRC) and cyber–physical systems (CPSs) are recognized as having the potential to impact and revolutionize the production landscape. A rich sensorization will be critical to such advances endowed with a large number of different sensors types (touch, temperature, pain, electrochemical, gas sensors, idiothetic sensing, etc.). Critical to these advances are the ways in which the technological advances are managed or made to develop electronic skin (e-skin) and the way it is employed to understand various dimensions of physical interaction in unconstrained environments [3] .

/pdf/flexible-electronic-skin-from-humanoids-to-humans-3er12h6tnq.pdf

Deji Akinwande

Papers

Flexible Electronic Skin: From Humanoids to Humans