Current-direction-controllable Ag-embedded stretchable layers to enhance and extend the applicability of stretchable sensors

Abstract

We suggest a multi-layered stretchable sensor with a carbon nanotube (CNT) layer enclosed by an embedded layer of silver (Ag-Ecoflex), and show how it can be used in biomedical applications. The current direction can be controlled along the vertical or lateral axis on the Ag-Ecoflex layer by adjusting the composite Ag ratio; the CNT layer can determine electrical conductivity from the bypassed current path. The multi-layered stretchable sensor can ensure electrical conductivity up to a maximum strain of 245% with a high resistance change of 3782% when Ag-Ecoflex concentration was increased to 60 wt%, showing an electrical resistance of 71.64 Ω/mm along its vertical axis. The sensor functioned normally on a heated state and for up to three weeks on an immersed state possessing a linear characteristic; it can be used for sensor calibration. We confirmed its reliability by 1000 cycles of the strain-release test, detected body motions and tissue swelling, applied it to intravesical cystometric test, and verified compatibility with analog-to-digital conversion in real-time. Resulting, this sensor can secure both high sensitivity and modulus of elasticity, proposing the stability of sensor by simulating the external environment and internal human body. This proposed multi-layered stretchy sensor is anticipated to have a wide range of wearable monitoring device applications.