A fluorine-based strong and healable elastomer with unprecedented puncture resistance for high performance flexible electronics.

There is usually a trade-off between high mechanical strength and dynamic self-healing because the mechanisms of these properties are mutually exclusive. Herein, we design and fabricate a fluorinated phenolic polyurethane (FPPU) elastomer based on octafluoro-4,4'-biphenol to overcome this challenge. This fluorine-based motif not only tunes interchain interactions through π-π stacking between aromatic rings and free-volume among polymer chains but also improves the reversibility of phenol-carbamate bonds via electron-withdrawing effect of fluorine atoms. The developed FPPU elastomer shows the highest recorded puncture energy (648.0 mJ), high tensile strength (27.0 MPa), as well as excellent self-healing efficiency (92.3%), along with low surface energy (50.9 MJ m-2), notch-insensitivity, and reprocessability compared with non-fluorinated counterpart biphenolic polyurethane (BPPU) elastomer. Taking advantage of the above-mentioned merits of FPPU elastomer, we prepare an anti-fouling triboelectric nanogenerator (TENG) with a self-healable, and reprocessable elastic substrate. Benefiting from stronger electron affinity of fluorine atoms than hydrogen atoms, this electronic device exhibits ultrahigh peak open-circuit voltage of 302.3 V compared to the TENG fabricated from BPPU elastomer. Furthermore, a healable and stretchable conductive composite is prepared. This research provides a distinct and general pathway toward constructing high-performance elastomers and will enable a series of new applications.

An Encapsulation-Free and Hierarchical Porous Triboelectric Scaffold with Dynamic Hydrophilicity for Efficient Cartilage Regeneration.

Tissue engineering and electrotherapy are two promising methods to promote tissue repair. However, their integration remains an underexplored area, because their requirements on devices are usually distinct. Triboelectric nanogenerators (TENGs) have shown great potential to develop self-powered devices. However, due to their susceptibility to moisture, TENGs have to be encapsulated in vivo. Therefore, existing TENGs cannot be employed as tissue engineering scaffolds, which require direct interaction with surrounding cells. Here, the concept of triboelectric scaffolds (TESs) is proposed. Poly(glycerol sebacate), a biodegradable and relatively hydrophobic elastomer, is selected as the matrix of TESs. Each hydrophobic micropore in multi-hierarchical porous TESs efficiently serves as a moisture-resistant working unit of TENGs. Integration of tons of micropores ensures the electrotherapy ability of TESs in vivo without encapsulation. Originally hydrophobic TESs are degraded by surface erosion and transformed into hydrophilic surfaces, facilitating their role as tissue engineering scaffolds. Notably, TESs seeded with chondrocytes obtain dense and large matured cartilages after subcutaneous implantation in nude mice. Importantly, rabbits with osteochondral defects receiving TES implantation show favorable hyaline cartilage regeneration and complete cartilage healing. This work provides a promising electronic biomedical device and will inspire a series of new in vivo applications.

Biodegradable Elastomers and Gels for Elastic Electronics.

Biodegradable electronics are considered as an important bio-friendly solution for electronic waste (e-waste) management, sustainable development, and emerging implantable devices. Elastic electronics with higher imitative mechanical characteristics of human tissues, have become crucial for human-related applications. The convergence of biodegradability and elasticity has emerged a new paradigm of next-generation electronics especially for wearable and implantable electronics. The corresponding biodegradable elastic materials are recognized as a key to drive this field toward the practical applications. The review first clarifies the relevant concepts including biodegradable and elastic electronics along with their general design principles. Subsequently, the crucial mechanisms of the degradation in polymeric materials are discussed in depth. The diverse types of biodegradable elastomers and gels for electronics are then summarized. Their molecular design, modification, processing, and device fabrication especially the structure-properties relationship as well as recent advanced are reviewed in detail. Finally, the current challenges and the future directions are proposed. The critical insights of biodegradability and elastic characteristics in the elastomers and gel allows them to be tailored and designed more effectively for electronic applications.

Multifunctional Thermoplastic Polyurea Based on the Synergy of Dynamic Disulfide Bonds and Hydrogen Bond Cross-Links.

Integrating the self-healing property with the shape-memory effect is a strategy that extends the service lifetime of shape-memory materials. However, this strategy is inadequate to reshape and recycle through the self-healing property or liquid-state remoldability. For more types of damage, solid-state plasticity is needed as a complementary mechanism to broaden the reprocessing channels of smart materials. In this study, multifunctional thermoplastic polyureas cross-linked by urea hydrogen bonds are prepared, which possess the multipathway remodeling property. The shape transition can be triggered after heating above 65 °C. The synergistic effect of dynamic disulfide bonds and hydrogen bonds causes the thermoplastic polyureas to possess characteristics similar to those of associative covalent adaptable networks. Thus, the polyureas can repair the damage or reconfigure the shape at 75 °C in 15 min by solid-state plasticity, instead of going into a viscous flow state. Soft grippers with various shapes are prepared by integration of solid-state plasticity, and the structure and function of the grippers can be repaired. The integration of solid-state plasticity and the self-healing property broadens the paths of shape-memory polymers in recyclability and reshapability.

A near-infrared light-triggered shape-memory polymer for long-time fluorescence imaging in deep tissues.

Implanting a stent in the body through a minimally invasive operation and tracking its location in real-time is still a challenge. Herein, a near-infrared (NIR) light-triggered shape-memory polymer possessing a long-time fluorescence imaging function has been developed by cross-linking 6-arm poly(ethylene glycol)-poly(ε-caprolactone) using a croconate dye YHD798 as the chemical crosslinker and NIR-absorption perssad. Due to the extraordinary photothermal conversion property of YHD798, the temperature of the material raised from 20 °C to 120 °C under 808 nm near-infrared irradiation at 0.4 W cm-2, leading to shape recovery in 50 s in a programmed shape-transition process. YHD798 also exerted an aggregation-induced emission effect, endowing the polymer with a clear NIR fluorescence imaging function even when covered by a 2 mm pork slab and could be used for the real-time visualization of the implanted device fabricated from this polymer in deep tissues of the body. When a tubular stent that was fabricated from this polymer, was implanted into the carotid artery of a Sprague-Dawley rat, it could recover to its permanent shape under 808 nm laser irradiation in 60 s owing to the shape-memory function and facilitated NIR-I fluorescence imaging after implantation for a week owing to the croconate dye. This work provides a new strategy for designing and developing smart polymers with NIR-light-triggered shape-memory effect and long-term fluorescence imaging function for biomedical applications.