Breathable and Stretchable Temperature Sensors Inspired by Skin

Abstract

Flexible electronics attached to skin for healthcare, such as epidermal electronics, has to struggle with biocompatibility and adapt to specified environment of skin with respect to breath and perspiration. Here, we report a strategy for biocompatible flexible temperature sensors, inspired by skin, possessing the excellent permeability of air and high quality of water-proof by using semipermeable film with porous structures as substrate. We attach such temperature sensors to underarm and forearm to measure the axillary temperature and body surface temperature respectively. The volunteer wears such sensors for 24 hours with two times of shower and the in vitro test shows no sign of maceration or stimulation to the skin. Especially, precise temperature changes on skin surface caused by flowing air and water dropping are also measured to validate the accuracy and dynamical response. The results show that the biocompatible temperature sensor is soft and breathable on the human skin and has the excellent accuracy compared to mercury thermometer. This demonstrates the possibility and feasibility of fully using the sensors in long term body temperature sensing for medical use as well as sensing function of artificial skin for robots or prosthesis.

Figure 1. Illustration of the design and function of the biocompatible and stretchable temperature sensor.

(a) Structure of the ultra-flexible temperature sensor on breathable film. (b) SEM image of the semipermeable film surface. (c) Cross section of the semipermeable film in SEM, (the film is pressed on the side face of the sample stage). (d) Micro-structure of the polyurethane layer (upper side) of the semipermeable film in SEM. (e) The illustration of water proof and vapor permeable property of the sensor.

Figure 2. Fabrication of the biocompatible and strechable temperature sensor.

(a) Fabrication flow chat.(b) Transfer-printing in solution. (c) The stretchable sensors on the glass sheet with packaging, the inset is the image of the CNT film contacting with the pad. (d) The SEM image of the sensor, the inset is the optical microscopy image of the sensor under bending deformation.

Figure 3. Performance of the biocompatible and stretchable temperature sensor.

(a) Calibration results with inset showing the calibration setting. (b) In vitro test of the sensor and its comparison with the mercury thermometer. (c) Wearing the device for 24 hours with 2 times of shower. (d) The skin under the device after 24 hours’ wearing, no sign of maceration or stimulation is observed.

Figure 4. Demonstration of the sensing of water dropping and blowing by mouth, and the noise analysis experiment.

(a) Temperature change in water dropping (with video in the supporting materials). (b) Temperature change in mouth blowing. (c) Resistance change under stretching deformation measured with universal tensile testing machine. (d) Resistance change while the arm twisting and rotating (with video in the supporting materials).