Facile Preparation of Dual Functional Wearable Devices Based on Hindered Urea Bond-Integrated Reprocessable Polyurea and AgNWs

The Latest Advances in Mechanically Robust Self-Healing Polyurea Based on Dynamic Chemistry

Polyureas are widely used in many fields such as civil, industry, and defense due to their excellent performance and structural adjustable properties. The development of self-healing polyurea materials with high strength and toughness, key connotations of their advanced applications, is both fascinating and challenging because these properties are associated with conflicting structural features, making it difficult to optimize these contradictory properties in a single material. In this review, the relationship between polyurea structure and performance is discussed, and the design strategy of self-healing polyurea networks based on dynamic interactions that allow for balancing high mechanical performance and repairability is delineated from a molecular design point of view. Lastly, a summary of the potential applications of polyurea in the fields of sensing, protective coatings, and recycling, as well as possible future challenges, is presented.

2D Polyamides Enable Self-Healing and Recyclable Elastomers with High Robustness, Toughness, and Crack Resistance via Supramolecular Interactions

High-performance elastomers with exceptional mechanical properties and self-healing capabilities have garnered significant attention due to their wide range of potential applications. However, designing elastomers that strike a balance between self-healing capabilities and mechanical properties remains a considerable challenge. Inspired by biological cartilage, a highly robust, tough, and crack-resistant self-healing elastomer is presented by incorporating hydrogen-bond-rich 2D polyamide (2DPA) into a poly(urethane-urea) matrix. This integration enhances supramolecular interactions driven by multiple hydrogen bonds. The resulting elastomer exhibits impressive strength (54.6 MPa), remarkable elongation at break (705.4%), exceptional toughness (116.7 MJ m-3), outstanding crack resistance (fracture energy up to 187.2 kJ m-2), high self-healing efficiency (98.9% at 50 °C for 9 h, 97.9% at room temperature for 48 h), and excellent recyclability, capable of lifting ≈40 000 times its own weight. Furthermore, a damage-tolerant, fatigue-resistant anticorrosive coating from this elastomer, showcasing its potential for protective skin applications in underwater robotics is developed. The underlying enhancement mechanism is validated through testing of various elastomers and molecular dynamics simulations, confirming the potential of engineering 2DPA for high-performance elastomers by leveraging supramolecular interactions.

Instantaneous self-recovery and ultra-low detection limit hydrogel electronic sensor for temporomandibular disorders intelligent diagnosis

Temporomandibular disorders (TMD) intelligent diagnosis promises to elevate clinical efficiency and facilitate timely TMD management for patients. However, development of TMD intelligent diagnostic tools with high accuracy and sensitivity presents challenges, particularly in sensing minute deformations and ensuring rapid self-recovery. Here we report a biocompatible hydrogel electronic sensor with instantaneous self-recovery (within 2.1 s) and ultra-low detection limit (0.005% strain). It could efficiently diagnose disc displacement with reduction (DDwR) with satisfactory accuracy of 90.00%, and also had a clear indication of the typical clinical manifestations of DDwR and the timing of temporomandibular joint (TMJ) clicking, with a sensitivity of up to 100% in human compared to the diagnostic criteria for TMD (DC/TMD). Furthermore, a predictive model based on waveform features achieved 84.4% accuracy and 86% sensitivity, reducing dependence on physicians. In summary, the hydrogel sensor is expected to become a radiation-free, non-invasive, practical and effective tool for future TMD diagnosis.

Non-Isocyanate Synthesis of Covalent Adaptable Networks Based on Dynamic Hindered Urea Bonds: Sequential Polymerization and Chemical Recycling

The development of environmentally sustainable processes for polymer recycling is of paramount importance in the polymer industry. In particular, the implementation of chemical recycling for thermoset polymers via covalent adaptable networks (CANs), particularly those based on the dynamic hindered urea bond (HUB), has garnered intensive attention from both the academic and industrial sectors. This interest stems from its straightforward chemical structure and reaction mechanism, which are well-suited for commercial polyurethane and polyurea applications. However, a substantial drawback of these CANs is the requisite use of toxic isocyanate curing agents for their synthesis. Herein, we propose a new HUB synthesis pathway involving thiazolidin-2-one and a hindered amine. This ring-opening reaction facilitates the isocyanate-free formation of a HUB and enables sequential reactions with acrylate and epoxide monomers via thiol-Michael and thiol-epoxy click chemistry. The CANs synthesized using this methodology exhibit superior reprocessability, chemical recyclability, and reutilizability, facilitated by specific catalytic and solvent conditions, through the reversible HUB, thiol-Michael addition, and transesterification processes.

Stretchable Organohydrogel with Adhesion, Self-Healing, and Environment-Tolerance for Wearable Strain Sensors

Stretchable hydrogels as landmark soft materials have been efficiently utilized in the field of wearable sensing devices. However, these soft hydrogels mostly cannot integrate transparency, stretchability, adhesiveness, self-healing, and environmental adaptability into one system. Herein, a fully physically cross-linked poly(hydroxyethyl acrylamide)-gelatin dual-network organohydrogel is prepared in a phytic acid-glycerol binary solvent via a rapid ultraviolet light initiation. The introduction of gelatin as the second network endows the organohydrogel with desirable mechanical performance (high stretchability up to 1240%). The presence of phytic acid not only synergizes with glycerol to impart environment-tolerance to the organohydrogel (from -20 to 60 °C) but also increases the conductivity. Moreover, the organohydrogel demonstrates a durable adhesive performance toward diverse substrates, a high self-healing efficiency through heat treatment, and favorable optical transparency (transmittance of 90%). Furthermore, the organohydrogel achieves high sensitivity (gauge factor of 2.18 at 100% strain) and rapid response time (80 ms) and could detect both tiny (a low detection limit of 0.25% strain) and large deformations. Therefore, the assembled organohydrogel-based wearable sensors are capable of monitoring human joint motions, facial expression, and voice signals. This work proposes a facile route for multifunctional organohydrogel transducers and promises the practical application of flexible wearable electronics in complex scenarios.

Thermal and UV light adaptive polyurethane elastomers for photolithography-transfer printing of flexible circuits

Flexible polymers are widely used in the fields of wearable devices, soft robots, sensors, and other flexible electronics. Combining high strength and elasticity, electrical conductivity, self-healability, and surface tunable properties in one material becomes a challenge for designing polymeric materials for these applications, especially in flexible electronics. Herein, we propose a "two birds with one stone" strategy to synthesize thermal and UV light adaptive polyurethane elastomers with high-strength, self-healable, surface-modifiable and patternable functions for photolithography-transfer printing flexible circuits. The "stone", dihydroxybenzophenone, plays two roles in the synthesized polyurethanes as both a dynamic covalent bond and a UV-sensitive unit. On one hand, the phenolic group reacts with isocyanate to form a dynamic covalent phenol-carbamate bond, making the polymer self-healable, processable, and surface-embeddable with conductive fillers utilizing dynamic network rearrangement. On the other hand, the benzophenone group acts as a UV-sensitive unit to graft other functional groups to the polymer surface or self-crosslink on the surface under UV irradiation. Based on the dynamic covalent network and UV self-crosslinking properties, self-healable patterned flexible circuits can be obtained by photolithography-transfer printing. The flexible circuits prepared by loading silver nanowires on the dynamically crosslinked polyurethane substrate show little change of electric resistance when stretched up to 125% and can withstand thousands of stretching cycles.