Metallosupramolecular Photonic Elastomers with Self‐Healing Capability and Angle‐Independent Color

Photonic elastomers that can change colors like a chameleon have shown great promise in various applications. However, it still remains a challenge to produce artificial photonic elastomers with desired optical and mechanical properties. Here, the generation of metallosupramolecular polymer‐based photonic elastomers with tunable mechanical strength, angle‐independent structural color, and self‐healing capability is reported. The photonic elastomers are prepared by incorporating isotropically arranged monodispersed SiO₂ nanoparticles within a supramolecular elastomeric matrix based on metal coordination interaction between amino‐terminated poly(dimethylsiloxane) and cerium trichloride. The photonic elastomers exhibit angle‐independent structural colors, while Young's modulus and elongation at break of the as‐formed photonic elastomers reach 0.24 MPa and 150%, respectively. The superior elasticity of photonic elastomers enables their chameleon‐skin‐like mechanochromic capability. Moreover, the photonic elastomers are capable of healing scratches or cuts to ensure sustainable optical and mechanical properties, which is crucial to their applications in wearable devices, optical coating, and visualized force sensing.     

Tough and Water‐Insensitive Self‐Healing Elastomer for Robust Electronic Skin

An electronic (e‐) skin is expected to experience significant wear and tear over time. Therefore, self‐healing stretchable materials that are simultaneously soft and with high fracture energy, that is high tolerance of damage or small cracks without propagating, are essential requirements for the realization of robust e‐skin. However, previously reported elastomers and especially self‐healing polymers are mostly viscoelastic and lack high mechanical toughness. Here, a new class of polymeric material crosslinked through rationally designed multistrength hydrogen bonding interactions is reported. The resultant supramolecular network in polymer film realizes exceptional mechanical properties such as notch‐insensitive high stretchability (1200%), high toughness of 12 000 J m^?2, and autonomous self‐healing even in artificial sweat. The tough self‐healing materials enable the wafer‐scale fabrication of robust and stretchable self‐healing e‐skin devices, which will provide new directions for future soft robotics and skin prosthetics.     

Self‐Healing Hydrogels

Over the past few years, there has been a great deal of interest in the development of hydrogel materials with tunable structural, mechanical, and rheological properties, which exhibit rapid and autonomous self‐healing and self‐recovery for utilization in a broad range of applications, from soft robotics to tissue engineering. However, self‐healing hydrogels generally either possess mechanically robust or rapid self‐healing properties but not both. Hence, the development of a mechanically robust hydrogel material with autonomous self‐healing on the time scale of seconds is yet to be fully realized. Here, the current advances in the development of autonomous self‐healing hydrogels are reviewed. Specifically, methods to test self‐healing efficiencies and recoveries, mechanisms of autonomous self‐healing, and mechanically robust hydrogels are presented. The trends indicate that hydrogels that self‐heal better also achieve self‐healing faster, as compared to gels that only partially self‐heal. Recommendations to guide future development of self‐healing hydrogels are offered and the potential relevance of self‐healing hydrogels to the exciting research areas of 3D/4D printing, soft robotics, and assisted health technologies is highlighted.     

Self‐Healing Materials

Self‐healing materials are able to partially or completely heal damage inflicted on them, e.g., crack formation; it is anticipated that the original functionality can be restored. This article covers the design and generic principles of self‐healing materials through a wide range of different material classes including metals, ceramics, concrete, and polymers. Recent key developments and future challenges in the field of self‐healing materials are summarised, and generic, fundamental material‐independent principles and mechanism are discussed and evaluated.     

Tough,Self‐Healing Hydrogels Capable of Ultrafast Shape Changing

Achieving multifunctional shape‐changing hydrogels with synergistic and engineered material properties is highly desirable for their expanding applications, yet remains an ongoing challenge. The synergistic design of multiple dynamic chemistries enables new directions for the development of such materials. Herein, a molecular design strategy is proposed based on a hydrogel combining acid–ether hydrogen bonding and imine bonds. This approach utilizes simple and scalable chemistries to produce a doubly dynamic hydrogel network, which features high water uptake, high strength and toughness, excellent fatigue resistance, fast and efficient self‐healing, and superfast, programmable shape changing. Furthermore, deformed shapes can be memorized due to the large thermal hysteresis. This new type of shape‐changing hydrogel is expected to be a key component in future biomedical, tissue, and soft robotic device applications.     

Highly Dynamic Nanocomposite Hydrogels Self‐Assembled by Metal Ion‐Ligand Coordination

Hydrogels are emerging biomaterials with desirable physicochemical characteristics. Doping of metal ions such as Ca²⁺, Mg²⁺, and Fe²⁺ provides the hydrogels with unique attributes, including bioactivity, conductivity, and tunability. Traditionally, this doping is achieved by the interaction between metal ions and corresponding ligands or the direct incorporation of as‐prepared metal‐based nanoparticles (NPs). However, these approaches rely on a complex and laborious preparation and are typically restricted to few selected ion species. Herein, by mixing aqueous solutions of ligands (bisphosphonates, BPs), polymer grafted with ligands, and metal ions, a series of self‐assembled metallic‐ion nanocomposite hydrogels that are stabilized by the in situ formed ligand‐metal ion (BP‐M) NPs are prepared. Owing to the universal coordination between BPs and multivalent metal ions, the strategy is highly versatile and can be generalized for a wide array of metal ions. Such hydrogels exhibit a wide spectrum of mechanical properties and remarkable dynamic properties, such as excellent injectability, rapid stress relaxation, efficient ion diffusion, and triggered disassembly for harvesting encapsulated cells. Meanwhile, the hydrogels can be conveniently coated or patterned onto the surface of metals via electrophoresis. This work presents a universal strategy to prepare designer nanocomposite materials with highly tunable and dynamic behaviors.     

Tough Self‐Healing Elastomers by Molecular Enforced Integration of Covalent and Reversible Networks

Self‐healing polymers crosslinked by solely reversible bonds are intrinsically weaker than common covalently crosslinked networks. Introducing covalent crosslinks into a reversible network would improve mechanical strength. It is challenging, however, to apply this concept to “dry” elastomers, largely because reversible crosslinks such as hydrogen bonds are often polar motifs, whereas covalent crosslinks are nonpolar motifs. These two types of bonds are intrinsically immiscible without cosolvents. Here, we design and fabricate a hybrid polymer network by crosslinking randomly branched polymers carrying motifs that can form both reversible hydrogen bonds and permanent covalent crosslinks. The randomly branched polymer links such two types of bonds and forces them to mix on the molecular level without cosolvents. This enables a hybrid “dry” elastomer that is very tough with fracture energy 13500 Jm^?2 comparable to that of natural rubber. Moreover, the elastomer can self‐heal at room temperature with a recovered tensile strength 4 MPa, which is 30% of its original value, yet comparable to the pristine strength of existing self‐healing polymers. The concept of forcing covalent and reversible bonds to mix at molecular scale to create a homogenous network is quite general and should enable development of tough, self‐healing polymers of practical usage.     

An Elastic Autonomous Self‐Healing Capacitive Sensor Based on a Dynamic Dual Crosslinked Chemical System

Adopting self‐healing, robust, and stretchable materials is a promising method to enable next‐generation wearable electronic devices, touch screens, and soft robotics. Both elasticity and self‐healing are important qualities for substrate materials as they comprise the majority of device components. However, most autonomous self‐healing materials reported to date have poor elastic properties, i.e., they possess only modest mechanical strength and recoverability. Here, a substrate material designed is reported based on a combination of dynamic metal‐coordinated bonds (β‐diketone–europium interaction) and hydrogen bonds together in a multiphase separated network. Importantly, this material is able to undergo self‐healing and exhibits excellent elasticity. The polymer network forms a microphase‐separated structure and exhibits a high stress at break (≈1.8 MPa) and high fracture strain (≈900%). Additionally, it is observed that the substrate can achieve up to 98% self‐healing efficiency after 48 h at 25 °C, without the need of any external stimuli. A stretchable and self‐healable dielectric layer is fabricated with a dual‐dynamic bonding polymer system and self‐healable conductive layers are created using polymer as a matrix for a silver composite. These materials are employed to prepare capacitive sensors to demonstrate a stretchable and self‐healable touch pad.     

Self‐Healing Micellar Ion Gels Based on Multiple Hydrogen Bonding

Ion gels, composed of macromolecular networks filled by ionic liquids (ILs), are promising candidate soft solid electrolytes for use in wearable/flexible electronic devices. In this context, the introduction of a self‐healing function would significantly improve the long‐term durability of ion gels subject to mechanical loading. Nevertheless, compared to hydrogels and organogels, the self‐healing of ion gels has barely investigated been because of there being insufficient understanding of the interactions between polymers and ILs. Herein, a new class of supramolecular micellar ion gel composed of a diblock copolymer and a hydrophobic IL, which exhibits self‐healing at room temperature, is presented. The diblock copolymer has an IL‐phobic block and a hydrogen‐bonding block with hydrogen‐bond‐accepting and donating units. By combining the IL and the diblock copolymer, micellar ion gels are prepared in which the IL phobic blocks form a jammed micelle core, whereas coronal chains interact with each other via multiple hydrogen bonds. These hydrogen bonds between the coronal chains in the IL endow the ion gel with a high level of mechanical strength as well as rapid self‐healing at room temperature without the need for any external stimuli such as light or elevated temperatures.