Nature-Inspired Molecular-Crowding Enabling Wide-Humidity Range Applicable, Anti-Freezing, and Robust Zwitterionic Hydrogels for On-Skin Electronics.

Hydrogels are currently in the limelight for applications in soft electronics but they suffer from the tendency to lose water or freeze when exposed to dry environments or low temperatures. Molecular crowding is a prevalent occurrence in living cells, in which molecular crowding agents modify the hydrogen bonding structure, causing a significant reduction in water activity. Here, a wide-humidity range applicable, anti-freezing, and robust hydrogel is developed through the incorporation of natural amino acid proline (Pro) and conductive MXene into polyvinyl alcohol (PVA) hydrogel networks. Theoretical calculations reveal that Pro can transform "free water" into "locked water" via the molecular-crowding effect, thereby suppressing water evaporation and ice forming. Accordingly, the prepared hydrogel exhibits high water retention capability, with 77% and 55% being preserved after exposure to 20 °C, 28% relative humidity (RH) and 35 °C, 90% RH for 12 h. Meanwhile, Pro lowers the freezing temperature of the hydrogel to 34 °C and enhances its stretchability and strength. Finally, the PVA/Pro/MXene hydrogels are assembled as multifunctional on-skin strain sensors and conductive electrodes to monitor human motions and detect tiny electrophysiological signals. Collectively, this work provides a molecular crowding strategy that will motivate researchers to develop more advanced hydrogels for versatile applications.

Knittable and Sewable Spandex Yarn with Nacre-Mimetic Composite Coating for Wearable Health Monitoring and Thermo- and Antibacterial Therapies.

The emerging personal healthcare has significantly propelled the development of advanced wearable electronics with novel functions of providing diagnostic information and point-of-care therapies for specific diseases. However, it is still challenging to simultaneously achieve high sensitivity for health biomonitoring and multifunction integration for point-of-care therapies in a one single flexible, lightweight yet robust fiber-based device. Here, a knittable and sewable spandex yarn with conductive nacre-mimetic composite coating has been developed through an alternant dip-coating method employing MXene nanosheets as the "brick" and polydopamine (PDA)/Ni2+ as the "mortar". The resultant spandex yarn coating with MXene/PDA/Ni2+ (MPNi@Spandex) can be assembled as a strain sensor with high sensitivity (up to 5.7 × 104 for the gauge factor), wide sensing range (∼61.2%), and low detection limit (0.11%) to monitor the biological activities of the human body. Furthermore, MPNi@Spandex displays great potential to give on-demand thermotherapy by virtue of the fast response to near-infrared irradiation, controllable surface temperature, and applicability even under sewing conditions. In addition, MPNi@Spandex knitted textiles demonstrate a strong antibacterial effect due to the sharp edges, anionic, and hydrophilic nature of MXene nanosheets. Remarkably, near-infrared irradiation further improves the bacteria-killing efficiency of an MPNi@Spandex knitted textile to more than 99.9%. This work paves the way for the design of multifunctional wearable electronics with an all-in-one theranostic platform for personal healthcare.