Switching Monomer-to-Excimer Fluorescence by Noncovalent Interaction Competition Strategy

Noncovalent fluorescence switching materials with specific molecular packing motifs for desired performance are difficult to design accurately due to the complexity of intermolecular interactions. Herein, a noncovalent interaction competition strategy to design fluorescence-switching materials by fine-modulating hydrogen-bond and π–π interactions is proposed. Hydrogen bonds are generated by nitrogen/oxygen-containing units while π–π interactions are generated between polycyclic aromatic hydrocarbons. After these two interactions are balanced in strength, they attempt to induce the formation of respective molecule assemblies stably under controllable conditions. Through thermal stimulus produced by a laser, a reversible assembly transition with high-contrast monomer-to-excimer fluorescence switching is achieved, which demonstrates promising applications in rewritable optical recording and time-dependent anti-counterfeiting. This strategy provides a crucial step toward the controllable switching of supramolecular assembly for information handling.     

Molecular Stacking Induced by Intermolecular C–H···N Hydrogen Bonds Leading to High Carrier Mobility in Vacuum‐Deposited Organic Films

Simple bottom‐up fabrication processes for molecular self‐assembly have been developed for the construction of higher‐order structures using organic materials, and have contributed to maximization of the potential of organic materials in chemical and bioengineering. However, their application to organic thin‐film devices such as organic light‐emitting diodes have not been widely considered because simple fabrication of a solid film containing an internal self‐assembly structure has been regarded as difficult. Here it is shown that the intermolecular C–H···N hydrogen bonds can be simply formed even in vacuum‐deposited organic films having flat interfaces. By designing the molecules containing pyridine rings properly for the intermolecular interaction, one can control the molecular stacking induced by the intermolecular hydrogen bonds. It is also demonstrated that the molecular stacking contributes to the high carrier mobility of the film. These findings provide new guidelines to improve the performance of organic optoelectronic devices and open up the possibilities for further development of organic devices with higher‐order structures.     

Autonomic Recovery of Fiber/Matrix Interfacial Bond Strength in a Model Composite

Autonomic self‐healing of interfacial damage in a model single‐fiber composite is achieved through sequestration of ca. 1.5 μm diameter dicyclopentadiene (DCPD) healing‐agent‐filled capsules and recrystallized Grubbs’ catalyst to the fiber/matrix interface. When damage initiates at the fiber/matrix interface, the capsules on the fiber surface rupture, and healing agent is released into the crack plane where it contacts the catalyst, initiating polymerization. A protocol for characterizing the efficiency of interfacial healing for the single‐fiber system is established. Interfacial shear strength (IFSS), a measure of the bond strength between the fiber and matrix, is evaluated for microbond specimens consisting of a single self‐healing functionalized fiber embedded in a microdroplet of epoxy. The initial (virgin) IFSS is equivalent or enhanced by the addition of capsules and catalyst to the interface and up to 44% average recovery of IFSS is achieved in self‐healing samples after full interfacial debonding. Examination of the fracture interfaces by scanning electron microscopy reveals further evidence of a polyDCPD film in self‐healing samples. Recovery of IFSS is dictated by the bond strength of polyDCPD to the surrounding epoxy matrix.     

Self‐healing Fibers: Autonomic Recovery of Fiber/Matrix Interfacial Bond Strength in a Model Composite (Adv. Funct. Mater. 20/2010)

Autonomic self‐healing of interfacial damage in a model single‐fiber composite is achieved through sequestration of ca. 1.5 μm diameter dicyclopentadiene (DCPD) healing‐agent‐filled capsules and recrystallized Grubbs’ catalyst to the fiber/matrix interface. When damage initiates at the fiber/matrix interface, the capsules on the fiber surface rupture, and healing agent is released into the crack plane where it contacts the catalyst, initiating polymerization. A protocol for characterizing the efficiency of interfacial healing for the single‐fiber system is established. Interfacial shear strength (IFSS), a measure of the bond strength between the fiber and matrix, is evaluated for microbond specimens consisting of a single self‐healing functionalized fiber embedded in a microdroplet of epoxy. The initial (virgin) IFSS is equivalent or enhanced by the addition of capsules and catalyst to the interface and up to 44% average recovery of IFSS is achieved in self‐healing samples after full interfacial debonding. Examination of the fracture interfaces by scanning electron microscopy reveals further evidence of a polyDCPD film in self‐healing samples. Recovery of IFSS is dictated by the bond strength of polyDCPD to the surrounding epoxy matrix.     

Significant Enhancement of Proton Transport in Bioinspired Peptide Fibrils by Single Acidic or Basic Amino Acid Mutation

Bioinspired materials are extremely suitable for the development of biocompatible and environmentally friendly functional materials. Peptide‐based assemblies are remarkably attractive for such tasks, since they provide a simple way to fuse together functional and structural protein motifs in artificial materials. Motivated by this idea, it is shown here that the introduction of a single acidic, or basic, amino acid into the side chain of a heptameric self‐assembling peptide increases proton conduction in the resulting fibers by two orders of magnitude. This self‐doping effect is much more pronounced than the effect induced by the peptide's acidic and basic termini groups. Furthermore, the self‐doping process is found to be significantly more effective for acidic side chains than for basic ones due to both much more effective self‐doping process, resulting in an order of magnitude larger concentration of charge carriers for the acidic assemblies, and higher mobility of the formed charge carriers – almost threefolds in this case. This work facilitates the realization of unique bioinspired self‐assembled proton conducting materials that may find uses in the emerging bioprotonic technology. The presented design flexibility and, in particular, the ability to introduce both proton and proton holes further extend the usefulness of these materials.     

A Highly Stretchable and Self‐Healing Supramolecular Elastomer Based on Sliding Crosslinks and Hydrogen Bonds

The long application life and stable performance of stretchable electronics have been putting forward requirements for both higher mechanical properties and better self‐healing ability of polymeric substrates. However, for self‐healing materials, simultaneously improving stretchability and robustness is still challenging. Here, by incorporating sliding crosslinker (polyrotaxanes) and hydrogen bonds into a polymer, a highly stretchable and self‐healable elastomer with good mechanical strength is achieved. The elastomer exhibits very high stretchability, such that it can be stretched to 2800% with a fracture strength of 1.05 MPa. Moreover, the elastomer can achieve nearly complete self‐healing (93%) at 55 °C. Next, tensile tests under different temperatures, step extension experiments, and in situ small angle X‐ray scattering confirm that the excellent stretchability is attributed to the combined effects of sliding cyclodextrins along guest chains and hydrogen bonds. Furthermore, a strain sensor by coating the single‐wall carbon nanotubes onto the surface of the elastic substrate is fabricated.     

Increasing Photothermal Efficacy by Simultaneous Intra‐ and Intermolecular Fluorescence Quenching

Recently, using in situ self‐assembly‐induced fluorescence quenching (i.e., intermolecular quenching denoted herein) of a photothermal agent (PTA) to enhance its photothermal efficiency has proven to be a successful photothermal therapy (PTT) strategy. But to the best of current knowledge, using simultaneous intra‐ and intermolecular fluorescence quenching of a PTA to additionally increase its photothermal efficacy has not been reported. Herein, employing a click condensation reaction and a rationally designed PTA Biotin‐Cystamine‐Cys‐Lys(Cypate)‐CBT ( 1 ), a “smart” strategy is developed of intracellular simultaneous intra‐ and intermolecular fluorescence quenching and applied it to largely increase the photothermal efficacy of the agent both in vitro and in vivo. After being internalized by biotin receptor‐overexpressing cancer cells, 1 is reduced by intracellular glutathione to initiate a CBT‐Cys condensation reaction (intramolecular quenching) and self‐assembly (intermolecular quenching) to form the nanoparticles 1‐NPs (simultaneous intra‐ and intermolecular fluorescence quenching). Experimental results indicate that 1‐NPs have higher fluorescence quenching efficiency than the control PTAs [Thiazole‐Lys(Cypate)‐Benzothiazole]₂ ( 1‐Dimer , intramolecular quenching), and nanoparticles of Cystamine‐Cys(Fmoc)‐Lys(Cypate)‐CBT ( 1‐Fmoc‐NPs , intermolecular quenching). It is envisioned that, by replacing the biotin group on 1 with other targeting warheads, the “smart” strategy is ready to increase the photothermal therapeutic efficiency of their corresponding diseases.     

Covalent Surface Modification Effects on Single‐Walled Carbon Nanotubes for Targeted Sensing and Optical Imaging

Optical nanoscale technologies often implement covalent or noncovalent strategies for the modification of nanoparticles, whereby both functionalizations are leveraged for multimodal applications but can affect the intrinsic fluorescence of nanoparticles. Specifically, single‐walled carbon nanotubes (SWCNTs) can enable real‐time imaging and cellular delivery; however, the introduction of covalent SWCNT sidewall functionalizations often attenuates SWCNT fluorescence. Recent advances in SWCNT covalent functionalization chemistries preserve the SWCNT's pristine graphitic lattice and intrinsic fluorescence, and here, such covalently functionalized SWCNTs maintain intrinsic fluorescence‐based molecular recognition of neurotransmitter and protein analytes. The covalently modified SWCNT nanosensor preserves its fluorescence response towards its analyte for certain nanosensors, presumably dependent on the intermolecular interactions between SWCNTs or the steric hindrance introduced by the covalent functionalization that hinders noncovalent interactions with the SWCNT surface. These SWCNT nanosensors are further functionalized via their covalent handles with a targeting ligand, biotin, to self‐assemble on passivated microscopy slides, and these dual‐functionalized SWCNT materials are explored for future use in multiplexed sensing and imaging applications.     

Polymer Fiber Scaffolds for Bone and Cartilage Tissue Engineering

Successful regeneration of weight‐bearing bone defects and critical‐sized cartilage defects remains a major challenge in clinical orthopedics. In the past decades, biodegradable polymer materials with biomimetic chemical and physical properties have been rapidly developed as ideal candidates for bone and cartilage tissue engineering scaffolds. Due to their unique advantages over other materials of high specific‐surface areas, suitable mechanical strength, and tailorable characteristics, scaffolds made of polymer fibers have been increasingly used for the repair of bone and cartilage defects. This Review summarizes the preparation and compositions of polymer fibers, as well as their characteristics. More importantly, the applications of polymer fiber scaffolds with well‐designed structures or unique properties in bone, cartilage, and osteochondral tissue engineering have been comprehensively highlighted. On the whole, such a comprehensive summary affords constructive suggestions for the development of polymer fiber scaffolds in bone and cartilage tissue engineering.     

Molecular Engineering of “Click”‐Phospholes Towards Self‐Assembled Luminescent Soft Materials

Inspired by the self‐assembled bilayer structures of natural amphiphilic phospholipids, a new class of highly luminescent “click”‐phospholes with exocyclic alkynyl group at the phosphorus center is reported. These molecules can be easily functionalized with a self‐assembly group to generate neutral “phosphole‐lipids”. This novel approach retains the versatile reactivity of the phosphorus center, allowing further engineering of the photophysical and self‐assembly properties of the materials at a molecular level. The results of this study highlight the importance of being able to balance weak intermolecular interactions for controlling the self‐assembly properties of soft materials. Only molecules with the appropriate set of intermolecular arrangement/interactions show both organogel and liquid crystal mesophases with well‐ordered microstructures. Moreover, an efficient energy transfer of the luminescent materials is demonstrated and applied in the detection of organic solvent vapors.     

Self‐Protective Room‐Temperature Phosphorescence of Fluorine and Nitrogen Codoped Carbon Dots

The unstable triplet excited state is a core problem when developing self‐protective room temperature phosphorescence (RTP) in carbon dots (CDs). Here, fluorine and nitrogen codoped carbon dots (FNCDs) with long‐lived triplet excited states, emitting pH‐stabilized blue fluorescence and pH‐responsive green self‐protective RTP, are reported for the first time. The self‐protective RTP of FNCDs arises from n–π * electron transitions for C? N/C?N bonds with a small energy gap between singlet and triplet states at room temperature. Moreover, the interdot/intradot hydrogen bonds and steric protection of C? F bonds reduce quenching of RTP by oxygen at room temperature. The RTP emission of FNCDs shows outstanding reversibility, while the blue fluorescence emission has good pH stability. Based on these FNCDs, a data encoding/reading strategy for advanced anticounterfeiting is proposed via time‐resolved luminescence imaging techniques, as well as steganography of complex patterns.     

Producing Supramolecular Functional Materials Based on Fiber Network Reconstruction

Here, the creation of new supramolecular functional materials based on the reconstruction of three‐dimensional interconnecting self‐organized nanofiber networks by a surfactant is reported. The system under investigation is N‐lauroyl‐L ‐glutamic acid di‐n‐butylamide in propylene glycol. The architecture of networks is implemented in terms of surfactants, e.g. sorbitan monolaurate. The elastic performance of the soft functional material is either weakened or strengthened (up to 300% for the current system) by reconstructing the topology of a fiber network. A topology transition of gel fiber network from spherulite‐like to comb‐like to spherulite‐like is performed with the introduction of this surfactant. The Span 20 molecules are selectively adsorbed on the side surfaces of the crystalline fibers and promote the nucleation of side branches, giving rise to the transformation of the network architecture from spherulite‐like topology to comb‐like topology. At high surfactant concentrations, the occurrence of micelles may provide an increasing number of nucleation centers for spherulitic growth, leading to the reformation of spherulite‐like topology. An analysis on fiber network topology supports and verifies a perfect agreement between the topological behavior and the rheological behavior of the functional materials. The approach identified in this study opens up a completely new avenue in designing and producing self‐supporting supramolecular functional materials with designated macroscopic properties.     

Self‐Healing Materials for Energy‐Storage Devices

The booming development of electronics, electric vehicles, and grid storage stations has led to a high demand for advanced energy‐storage devices (ESDs) and accompanied attention to their reliability under various circumstances. Self‐healing is the ability of an organism to repair damage and restore function through its own internal vitality. Inspired by this, brilliant designs have emerged in recent years using self‐healing materials to significantly improve the lifespan, durability, and safety of ESDs. Extrinsic and intrinsic self‐healing materials and their working principles are first introduced. Then, the application of self‐healing materials in ESDs according to their self‐healing chemistry, including hydrogen bonds, electrostatic interactions, and borate ester bonds, are described in detail. Based on these, critical challenges and important future directions of self‐healing ESDs are discussed.     

Light‐Controlled,High‐Resolution Patterning of Living Engineered Bacteria Onto Textiles,Ceramics, and Plastic

Living cells can impart materials with advanced functions, such as sense‐and‐respond, chemical production, toxin remediation, energy generation and storage, self‐destruction, and self‐healing. Here, an approach is presented to use light to pattern Escherichia coli onto diverse materials by controlling the expression of curli fibers that anchor the formation of a biofilm. Different colors of light are used to express variants of the structural protein CsgA fused to different peptide tags. By projecting color images onto the material containing bacteria, this system can be used to pattern the growth of composite materials, including layers of protein and gold nanoparticles. This is used to pattern cells onto materials used for 3D printing, plastics (polystyrene), and textiles (cotton). Further, the adhered cells are demonstrated to respond to sensory information, including small molecules (IPTG and DAPG) and light from light‐emitting diodes. This work advances the capacity to engineer responsive living materials in which cells provide diverse functionality.     

Mechanically Robust,Self‐Healable,and Highly Stretchable “Living” Crosslinked Polyurethane Based on a Reversible C?C Bond

Stimuli‐responsive polymers built by reversible covalent bonds used to possess unbalanced mechanical properties. Here, a crosslinked polyurethane containing aromatic pinacol as a novel reversible C? C bond provider is synthesized, whose tensile strength and failure strain are tunable from 27.3 MPa to as high as 115.2 MPa and from 324% to 1501%, respectively, owing to the relatively high bond energy of the C? C bond of pinacol as well as the hydrogen bond between hard segments and semicrystalline soft segments. Moreover, the dynamic equilibrium of pinacol enables self‐healing and recycling of the polymer. Interestingly, the dynamic exchange among macromolecules, for the first time, successfully cooperates with solid‐state drawing that applies to thermoplastics, realizing strengthening of thermoset. Meanwhile, the radicals derived from homolysis of pinacol can repeatedly initiate polymerization of vinyl monomers. The fruitful outcomes of this work may create a series of promising new techniques.     

Mechanically Robust,Self‐Healable,and Highly Stretchable “Living” Crosslinked Polyurethane Based on a Reversible CC Bond

Stimuli‐responsive polymers built by reversible covalent bonds used to possess unbalanced mechanical properties. Here, a crosslinked polyurethane containing aromatic pinacol as a novel reversible C?C bond provider is synthesized, whose tensile strength and failure strain are tunable from 27.3 MPa to as high as 115.2 MPa and from 324% to 1501%, respectively, owing to the relatively high bond energy of the C?C bond of pinacol as well as the hydrogen bond between hard segments and semicrystalline soft segments. Moreover, the dynamic equilibrium of pinacol enables self‐healing and recycling of the polymer. Interestingly, the dynamic exchange among macromolecules, for the first time, successfully cooperates with solid‐state drawing that applies to thermoplastics, realizing strengthening of thermoset. Meanwhile, the radicals derived from homolysis of pinacol can repeatedly initiate polymerization of vinyl monomers. The fruitful outcomes of this work may create a series of promising new techniques.     

Self‐Healing Graphene Oxide Based Functional Architectures Triggered by Moisture

Self‐healing materials are capable of spontaneously repairing themselves at damaging sites without additional adhesives. They are important functional materials with wide applications in actuators, shape memorizing materials, smart coatings, and medical treatments, etc. Herein, this study reports the self‐healing of graphene oxide (GO) functional architectures and devices with the assistance of moisture. These GO architectures can completely restore their mechanical‐performance (e.g., compressibility, flexibility, and strength) after healing their broken sites using a little amount of water moisture. On the basis of this effective moisture‐triggered self‐healing process, this study develops GO smart actuators (e.g., bendable actuator, biomimetic walker, rotatable fiber motor) and sensors with self‐healing ability. This work provides a new pathway for the development of self‐healing materials for their applications in multidimensional spaces and functional devices.     

Biomimetic Supertough and Strong Biodegradable Polymeric Materials with Improved Thermal Properties and Excellent UV‐Blocking Performance

The preparation of biodegradable polymeric materials with both great strength and toughness remains a huge challenge. The natural spider silk exhibits a combined super high tensile strength and high fracture toughness (150–190 J g^?1), attributing to the hierarchically assembled nanophase separation and the densely organized sacrificial hydrogen bonds confined in the nanoscale granules. Herein, inspired by natural spider silk, a facile strategy is reported for the preparation of nanostructured biomimetic polymeric material by incorporating biomass‐derived lignosulfonic acid (LA) as interspersed nanoparticles into a biodegradable poly(vinyl alcohol) (PVA) matrix. The fabricated PVA/LA nanocomposite film exhibits the world's highest toughness of 172 (±5) J g^?1 among the PVA materials, as well as a powerful tensile strength of 98.2 MPa and a large breaking strain of 282%. The outstanding performance is attributed to the strain‐induced scattering of LA nanoparticles in the PVA matrix and the strong intermolecular sacrificial hydrogen bonds confined in the interphase. Moreover, after introducing the easily available green biomass LA, the prepared biomimetic polymer films show excellent ultraviolet‐blocking performance and good thermal stability. As both PVA and LA are biodegradable, this work presents an innovative design strategy for fully biodegradable robust polymeric materials with integrated strength and toughness.