E-skin key features. Images adapted from: self-healing [16] (Copyright © 2020, Springer Nature), stretchability [17] (Copyright © 2020, The American Association for the Advancement of Science), low thickness and conformability [18] (Copyright © 2020, Springer Nature), flexibility [19] (© 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.), self-powered (reprinted with permission from [20]. Copyright 2018 American Chemical Society, Washington, WA, USA), biodegradability and recyclability [21] (Copyright © 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim, Germany), biocompatibility [22] (Copyright © 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim, Germany), sweat induction/analysis [14].