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. 2017 Jun 21;3(6):e1700053. doi: 10.1126/sciadv.1700053

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Copyright © 2017 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).

This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial license, which permits use, distribution, and reproduction in any medium, so long as the resultant use is not for commercial advantage and provided the original work is properly cited.

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Fig. 5 — (A) Concept of a hydrogel smart skin, with a flexible unit bearing power supply, control, readout and communication units, and a stretchable transducer batch. PCB, printed circuit board. (B) Photograph of an untethered electronic hydrogel with four stretchable heating elements and adjoined temperature sensors strongly bonded to a PVA hydrogel. Battery, control, readout, and Bluetooth low energy communication electronics are hosted on a flexible circuit board. (C) Finite element (FE) simulation of the transducer batch with four heating elements enabled. (D) Corresponding infrared (IR) thermography image of the freestanding device. Dashed lines in (C) and (D) outline the heater and sensor metal traces. (E) Autonomous hydrogel electronic skin controlled and read out continuously via mobile phone, worn on a human wrist with all heaters activated. (F) Corresponding IR image after ~450 s with all heater elements activated. (G) Measured temperature evolution of the heater elements measured via IR thermography and (H) the sensor elements. Switching of the heating elements is indicated by vertical lines. Recorded temperature traces of the sensor elements (solid lines) are in excellent agreement with data taken from IR images (open squares). (I) Concept of thermally triggered drug delivery where the substance is enclosed in a lipid shell. Temperature increase melts the shell, releasing the drug into the hydrogel. (J) Thermally triggered diffusion of a green food colorant throughout the hydrogel matrix.