3D printed microstructured ultra-sensitive pressure sensors based on microgel-reinforced double network hydrogels for biomechanical applications.

Hydrogel-based wearable flexible pressure sensors have great promise in human health and motion monitoring. However, it remains a great challenge to significantly improve the toughness, sensitivity and stability of hydrogel sensors. Here, we demonstrate the fabrication of hierarchically structured hydrogel sensors by 3D printing microgel-reinforced double network (MRDN) hydrogels to achieve both very high sensitivity and mechanical toughness. Polyelectrolyte microgels are used as building blocks, which are interpenetrated with a second network, to construct super tough hydrogels. The obtained hydrogels show a tensile strength of 1.61 MPa, and a fracture toughness of 5.08 MJ m-3 with high water content. The MRDN hydrogel precursors exhibit reversible gel-sol transitions, and serve as ideal inks for 3D printing microstructured sensor arrays with high fidelity and precision. The microstructured hydrogel sensors show an ultra-high sensitivity of 0.925 kPa-1, more than 50 times that of plain hydrogel sensors. The hydrogel sensors are assembled as an array onto a shoe-pad to monitor foot biomechanics during gaiting. Moreover, a sensor array with a well-arranged spatial distribution of sensor pixels with different microstructures and sensitivities is fabricated to track the trajectory of a crawling tortoise. Such hydrogel sensors have promising application in flexible wearable electronic devices.

Superstretching MXene Composite Hydrogel as a Bidirectional Stress Response Thixotropic Sensor.

The arrival of the era of artificial intelligence is constantly advancing the development of flexible electronic materials. However, low mechanical properties, nonflexible signal transmission, and insensitive signal output have restricted their development as sensors. In this study, a superstretching MXene composite conductive hydrogel was developed with a tensile strain of more than 1800%. The hydrogel was used as a flexible wearable sensor to detect human motion signals in real time. High sensitivity was achieved using the sensor to discern multidirectional human motions, such as bending of human joints, throat vocalization, swallowing, and pulse beat. In addition, rapid resilience was observed for the MXene composite hydrogel after unloading reverse compressive stress, which can quickly cause a specific current response in the micropressure area without leaving any traces. This thixotropic sensor achieves a rapid response to bidirectional stress and has huge application prospects in the field of human body motion detection and national defense information encryption.

Low temperature in situ synthesis and the formation mechanism of various carbon-encapsulated nanocrystals by the electrophilic oxidation of metallocene complexes.

The core-shell nanostructures have the advantages of combining distinctive properties of varied materials and improved properties over their single-component counterparts. Synthesis approaches for this class of nanostructures have been intensively explored, generally involving multiple steps. Here, a general and convenient strategy is developed for one-step in situ synthesis of various carbon-encapsulated nanocrystals with a core-shell structure via a solid-state reaction of metallocene complexes with (NH4)2S2O8 in an autoclave at 200 °C. A variety of near-spherical and equiaxed nanocrystals with a small median size ranging from 6.5 to 50.6 nm are prepared as inner cores, including Fe7S8, Ni3S4 and NiS, CoS, TiO2, TiO2 and S8, ZrO2, (NH4)3V(SO4)3 and VO2, Fe7S8 and Fe3O4, MoS2 and MoO2. The worm-like carbon shell provides exclusive room for hundreds of nanocrystals separated from each other, preventing nanocrystal aggregation. The synergistic effect of ammonium and a strong oxidizing anion on the electrophilic oxidation of metallocene complexes containing a metal-ligand π bond contributes to the carbon formation at low temperature. It is considered that the cyclopentadienyl ligand in a metallocene complex will decompose into highly reactive straight chain olefinic pieces and the metal-olefin π interaction enables an ordered self-assembly of olefinic pieces on nanocrystals to partially form graphitizable carbon and a core-shell structure. The high capacity, good cycling behavior and rate capability of Fe7S8@C and Ni3S4 and NiS@C electrodes are attributed to the good protection and electrical conductivity of the carbon shell.