Highly breathable MWCNTs/TPU e-tattoo for physiological signal and motion tracking

Abstract

Epidermal electronics that conform to the human skin surface have garnered significant attention in recent years. Nonetheless, integrating the ultra-thin structure of these electronics with effective signal acquisition capabilities remains a challenge. This study introduces a dual-functional ultrathin electronic tattoo (e-tattoo) designed for both skin sensing and electrode applications. The e-tattoo features a two-layer architecture, with an ultrathin thermoplastic polyurethane (TPU) film exhibiting a microporous structure, fabricated via a straightforward wire rod coating technique. The micropores, ranging from 0.58 to 2.15 μm, endow the device with excellent breathability. The conductive layer is achieved through the spray deposition of multi-walled carbon nanotubes (MWCNTs). Experimental results demonstrate that the e-tattoo exhibits superior vapor permeability, with a water vapor permeability rate of 26.75 mg cm⁻² h⁻¹ at 37 °C, and a reduced electrode-skin interface impedance compared to conventional gel electrodes. This results in enhanced signal acquisition performance when used as skin electrodes for electrophysiological monitoring of ECG and sEMG signals. Additionally, the e-tattoo is capable of strain detection and exhibits high sensitivity, with a gauge factor (GF) of 15 within the 0–100 % strain range. It features a rapid response time of 102 ms and maintains robust cyclic stability over the course of 1100 operational cycles. We anticipate that this highly breathable e-tattoo will have great potential in the field of wearable electronics and may inspire the design of next-generation electronic skin for human-computer interaction and personalized medical applications.