Stretchable and hydrophobic eutectogel for underwater human health monitoring based on hierarchical dynamic interactions

An all-environmentally stable eutectogel by combination of hydrophobic deep eutectic solvent and polymer network is fabricated. The flexible eutectogel with extraordinary transparency could be adhered on human skin and detect the human physiology signal even in the aqueous environment. [Display omitted] •Eutectogel with superior underwater stability is fabricated by all hydrophobic structure.•The abundant ion-dipole interactions and phase separation within the eutectogel endow it with excellent toughness.•Eutectogel maintain stable adhesiveness for a long time under various harsh environments.•The water-resistant eutectogel is of great potential in underwater ECG monitoring and motion detecting. Although the deep eutectic solvent based gels (eutectogels) are considered to be the next-generation stretchable electronics, it is still greatly challenging to develop an all-environmentally stable eutectogel because of the high water sensitivity of the DES. Herein, a eutectogel with high transparency, tailorable stretchability, and water-resistant properties is reported. First, a novel colorless hydrophobic deep eutectic solvent (DES) with good conductivity (1.2 mS cm−1), and low viscosity is found by forming hydrogen bonding between amphiphilic hydrogen donor and non-hygroscopic hydrogen acceptor. Moreover, abundant ion–dipole interactions between the polymer networks and DES are designed into the eutectogels and verified by 2D infrared spectrum, resulting in ultra-durability of eutectogels in different circumstances (including pH 1–14, 30–90 RH% and 10–50 °C) for over 5 days. Furthermore, thanks to the ion–dipole interactions and phase separation induced by poor solvated hard polymer segments in DES, the eutectogel is endowed with tailorable mechanical property (0.1–0.8 MPa), long-term underwater adhesion capability (0.5 MPa on irons), high transparency (>93%) and excellent biocompatibility (>95%), which has never been seen in previously reported eutectogels. This hydrophobic eutectogel could be used as action recognition devices and vital sign monitor underwater, meeting the next generation of wearable devices.