Synergistically engineered adhesive MXene hydrogels for multimodal epidermal sensing and self-powered systems

The MXene-based conductive hydrogels hold great promise for skin-interfaced bioelectronics but are often hindered by the restacking and oxidation of MXene nanosheets, as well as poor interfacial adhesion. To address these challenges, we propose a synergistic surface-and-interlayer engineering strategy that integrates a mussel-inspired polydopamine (PDA) coating with waterborne polyurethane (WPU) intercalation, which yields stable WPU/PDA@MXene hybrids that effectively resist oxidation and sedimentation for over 60 days. When incorporated into a polyacrylamide (PAM) network, the resulting composite hydrogel, denoted as PUDMP, exhibits remarkable mechanical properties, including high stretchability (1212%), toughness (433 kJ·m⁻ 3 ), and strong multi-substrate adhesion (188 kPa). The PUDMP hydrogel demonstrates multifunctional sensing capabilities with a negative temperature coefficient (−1.62%·°C⁻ 1 ), a wide-range strain sensitivity with gauge factors of 1.23 (0–200%) and 2.70 (200–600%), fast response/recovery (102/100 ms), and stable performance over 1000 cycles. As an epidermal electrode, PUDMP reliably captures electrophysiological signals such as ECG and electrodermal activity; as a strain sensor, it accurately tracks both subtle facial motions and large joint movements. Furthermore, when integrated as the flexible ionic/conductive electrode in a contact-separation triboelectric nanogenerator, the system achieves an open-circuit voltage of up to 112 V and a peak areal power density of 1.058 W·m⁻2, enabling energy harvesting and self-powered motion sensing. This work provides an integrated solution to the dispersion, stability, and adhesion challenges of MXene-based hydrogels, offering a practical platform for next-generation self-powered wearable bioelectronics.