Stretchable, Transparent, Ultrasensitive, and Patchable Strain Sensor for Human–Machine Interfaces Comprising a Nanohybrid of Carbon Nanotubes and Conductive Elastomers

TLDR

Human–machine interfaces can be improved by multifunctional sensors that capture environmental, intentional, or physiological data from wearable or implantable platforms. This work presents a stretchable, transparent, ultrasensitive, patchable strain sensor composed of a sandwich‑like nanohybrid film of single‑wall carbon nanotubes and a polyurethane‑PEDOT:PSS conductive elastomer. The sensor is fabricated via environmentally benign water‑based solution processing, forming percolating networks between SWCNTs and PEDOT phases in a stacked PU‑PEDOT:PSS/SWCNT/PU‑PEDOT:PSS structure that tunes gauge factor, stability, and transparency. It achieves 100 % stretchability, 62 % optical transparency, and a gauge factor of 62, enabling reliable detection of facial expressions and eye movements when applied to skin, as experimentally verified.

Abstract

Interactivity between humans and smart systems, including wearable, body-attachable, or implantable platforms, can be enhanced by realization of multifunctional human–machine interfaces, where a variety of sensors collect information about the surrounding environment, intentions, or physiological conditions of the human to which they are attached. Here, we describe a stretchable, transparent, ultrasensitive, and patchable strain sensor that is made of a novel sandwich-like stacked piezoresisitive nanohybrid film of single-wall carbon nanotubes (SWCNTs) and a conductive elastomeric composite of polyurethane (PU)-poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (PEDOT:PSS). This sensor, which can detect small strains on human skin, was created using environmentally benign water-based solution processing. We attributed the tunability of strain sensitivity (i.e., gauge factor), stability, and optical transparency to enhanced formation of percolating networks between conductive SWCNTs and PEDOT phases at interfaces in the stacked PU-PEDOT:PSS/SWCNT/PU-PEDOT:PSS structure. The mechanical stability, high stretchability of up to 100%, optical transparency of 62%, and gauge factor of 62 suggested that when attached to the skin of the face, this sensor would be able to detect small strains induced by emotional expressions such as laughing and crying, as well as eye movement, and we confirmed this experimentally.