Skin-like hydrogel-elastomer based electrochemical device for comfortable wearable biofluid monitoring

Wearable sensors that can monitor physiological and metabolic conditions have been extensively investigated in recent years. However, the poor wearing experience caused by the mechanical mismatch of such integrated sensors and soft skin has not received inadequate attention. In this work, we propose a skin-like hydrogel-elastomer based electrochemical device for comfortable wearable biofluid monitoring, which employs a thin thermoplastic polyurethane (TPU) film as an interlayer to bridge stretchable hydrogels and conductive ink to maintain good electrical conductivity without compromising the mechanical flexibility. The prepared electrochemical device has a Young's modulus (0.37 MPa) similar to that of the skin, thereby greatly improving the conformality with the curved surface of the skin and the wearing comfort during exercise. The device can achieve monitoring pH, Na+ and K+ in sweat with high sensitivity (58.14 mV/pH for pH, 58.89 mV/ decade for Na+, and 59.11 mV/decade for K+), high specificity and high reproducibility, which maintains such excellent electrochemical performance even under 30 % strain without complicated external structural design. Such a skin-like hydrogel-elastomer based electrochemical device with excellent wearing comfort and mechanical deformability provide considerable potential for wearable biofluid monitoring in personalized health applications.