Polyurethane foam coated with a multi-walled carbon nanotube/polyaniline nanocomposite for a skin-like stretchable array of multi-functional sensors

Body-attachable sensors can be applied to electronic skin (e-skin) as well as safety forewarning and health monitoring systems. However, achieving facile fabrication of high-performance, cost-effective sensors with mechanical stability in response to deformation due to body movement is challenging. Herein we report the material design, fabrication and characteristics of a skin-like stretchable array of multi-functional (MF) sensors based on a single sensing material of polyurethane foam coated with multi-walled carbon nanotube/polyaniline nanocomposite, which enables simultaneous detection of body temperature, wrist pulse and ammonia gas. These sensors exhibit high sensitivity, fast response and excellent durability. Furthermore, the fabricated sensor array shows stable performance under biaxial stretching up to 50% and attachment to skin owing to the use of direct-printed Galinstan liquid metal interconnections. This work proposes a facile method for fabrication of high-performance, stretchable MF sensors via appropriate selection of sensor design and functional materials that are applicable to e-skin and health monitoring systems. Combining stretchy foams with conductive nanomaterials enables real-time temperature, pulse, and gas exposure sensing from a patient's skin. Interactive ‘e-skin’ devices need to resolve different stimuli into clear electronic signals while attached to a deformable substrate. To satisfy these challenging constraints, Jeong Sook Ha and colleagues at Korea University coated polyurethane foams with a nanocomposite made from multiwalled carbon nanotubes and polyaniline. The porous microstructure of this hybrid material imparted mechanical flexibility and high responsiveness to electrical resistance changes and output voltage induced by pressure and heat variations, respectively, while the polyaniline component made it selective to toxic ammonia gas. A prototype device in which the foam is sandwiched between thin-film electrodes and which uses an adhesive gel to attach to the skin showed a rapid response and an excellent durability when attached to the fingertips and the wrist. A skin-like stretchable multi-functional sensor array based on a combination of PU foam and MWCNT-PANI nanocomposite is demonstrated to simultaneously detect pressure, temperature and ammonia gas with high sensitivity. The integrated sensor array with printed liquid metal interconnections operates stably under applied strain due to its attachment to the skin and under a biaxial strain up to 50%.