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Elastomers with high mechanical toughness can guarantee their durability during service life. Self-healing ability, as well as recyclability, can also extend the life of materials and save the consuming cost of the materials. Many efforts have been dedicated to promoting the mechanical toughness as well as the self-healing capability of elastomers at the same time, while it remains a challenge to balance the trade-off between the above properties in one system. Herein we proposed a molecular design driven by dual interactions of acylsemicarbazide hydrogen bonding and Cu2+-neocuproine coordination simultaneously. By introducing the reversible multiple hydrogen bonds and strong coordination bonds, we successfully fabricated an extremely tough and self-healing elastomer. The elastomer can achieve an impressive top-notch toughness of 491 MJ/m3. Furthermore, it boasted rapid elastic restorability within 10 min and outstanding crack tolerance with high fracture energy (152.6 kJ/m2). Benefiting from the combination of dynamic interactions, the material was able to self-repair under 80 °C conveniently and could be reprocessed to restore the exceptional mechanical properties. [ABSTRACT FROM AUTHOR]

The fabrication of 2,6‐bis(1,2,3‐triazol‐4yl)pyridine (btp) based metallo‐supramolecular gels has been mainly focusing on organogels. Only recently, the synthesis and metallo‐supramolecular hydrogel formation of linear poly(ethylene glycol) (PEG) with multiple btp units in the main chain are reported. In this manuscript, metallo‐supramolecular hydrogels that are constructed using tetra‐arm star PEG‐modified with btp end‐groups upon complexation with transition metal ions are reported. This btp‐functionalized star‐PEG precursor is more easily accessible and more defined than the previously reported linear system while also yielding stronger hydrogels. The gelation is selectively induced by Ni2+ ions and strongly depended on the metal‐ligand ratio and polymer concentration. The successful formation of organogels can be induced selectively by Ni2+ or Fe2+ ion complexation in acetonitrile, which leads to the strongest complexes. The inability to form hydrogels with Fe2+ ions is ascribed to the partial oxidation of Fe2+ to Fe3+ ions in an aqueous solution. Furthermore, the optimal conditions for achieving self‐healing capabilities are also determined (i.e., 4 wt% polymer concentration and btp:Ni2+ molar ratio of 2:1) using rheology. The high strain resistance and fast self‐healing characteristics make these specific Ni2+ metallo‐supramolecular hydrogels a promising platform for materials design with potential applications in supramolecular chemistry, coordination chemistry, and catalysis. [ABSTRACT FROM AUTHOR]

We investigate the fracture properties of poly(acrylamide-co-1-vinylimidazole) dual crosslink hydrogels [P(AAm-co-VIm)-M2+ gels] containing a small fraction of covalent bonds and a majority of dynamic bonds based on metal coordination bonds (Ni2+ or Zn2+). Unlike a previous study on a different dual crosslink hydrogel system having slower dynamic bonds based on poly(vinylalcohol) and borate ions (PVA-Borax gels), the presence of these faster dynamic coordination bonds has two main effects: They significantly toughen the P(AAm-co-VIm)-M2+ gels even at high stretch rates, where the dynamic bonds should in principle behave as covalent bonds at the crack tip, and they toughen the gels at very low stretch rates, where the dynamic bonds are invisible during the loading stage. We propose two additional molecular mechanisms to rationalize this behavior of P(AAm-co-VIm)-M2+ gels: we hypothesize that fast exchanging dynamic bonds remain slow compared to the characteristic time of bond scission and are, therefore, able to share the load upon covalent bond scission even at low loading rates. We also argue of the existence of longer-lived clusters of dynamic bonds that introduce a stretch rate-dependent strain hardening in uniaxial tension and stabilize and increase the size of the dissipative zone at the crack tip, thereby introducing a strain-dependent dissipative mechanism. [ABSTRACT FROM AUTHOR]

Bioadhesive gels with robust adhesion on wet and irregular tissue surfaces are desirable for clinical applications. Assembly of bioadhesive powders is an effective strategy for obtaining gels that adhere to wet and irregular tissue surfaces by absorbing interfacial water. However, current bioadhesive powders lack positive biological functions and are prone to postoperative adhesion. Here, we present a powder strategy based on metal-ligand coordination to create a series of bioadhesive polyacrylic acid (PAA) gels. In the gel network, metal ions (Mn+) are used to coordinate with the carboxy ligands of PAA to form dynamic noncovalent crosslinks. The powders can absorb interfacial water and assemble into gels on wet and irregular tissue surfaces within a few seconds, forming an initial adhesion layer by electrostatic interactions. Furthermore, the polymers can diffuse into the tissue matrix, and metal-ligand coordination is reconstructed to enhance the adhesion. Moreover, with a cationic shield layer, the bioadhesive powders can effectively avoid postoperative adhesion. Importantly, ions endow the gel with customized biological functions. We demonstrate that the hemostatic, antibacterial, peroxidase-like catalytic, and photodetachment abilities of the gels by incorporating different Mn+ ions. These advantages make the bioadhesive powder a promising platform for diverse tissue repair applications. [ABSTRACT FROM AUTHOR]

At this time, the development of advanced elastic dielectric materials for use in organic devices, particularly in organic field-effect transistors, is of considerable interest to the scientific community. In the present work, flexible poly(dimethylsiloxane) (PDMS) specimens cross-linked by means of ZnCl2-bipyridine coordination with an addition of 0.001 wt. %, 0.0025 wt. %, 0.005 wt. %, 0.04 wt. %, 0.2 wt. %, and 0.4 wt. % of gold nanoparticles (AuNPs) were prepared in order to understand the effect of AuNPs on the electrical properties of the composite materials formed. The broadband dielectric spectroscopy measurements revealed one order of magnitude decrease in loss tangent, compared to the coordinated system, upon an introduction of 0.001 wt. % of AuNPs into the polymeric matrix. An introduction of AuNPs causes damping of conductivity within the low-temperature range investigated. These effects can be explained as a result of trapping the Cl− counter ions by the nanoparticles. The study has shown that even a very low concentration of AuNPs (0.001 wt. %) still brings about effective trapping of Cl− counter anions, therefore improving the dielectric properties of the investigated systems. The modification proposed reveals new perspectives for using AuNPs in polymers cross-linked by metal-ligand coordination systems. [ABSTRACT FROM AUTHOR]

Polymers are at the core of emerging flexible sensor and soft actuator technology. Ideal candidates not only respond to external stimuli but also have programmable response intensity and speed. Incorporating dynamic interactions into polymers has been widely studied. However, most research has focused on synthesis methods and on optical and mechanical effects of these interactions. Here, a new and tunable method of enabling environmentally adaptive polymers are introduced. Specifically, polar functionalities are "hidden" within polydimethylsiloxane (PDMS). When unveiled, these polar functionalities change the hydrophilicity of the polymer. Water is the stimulus that triggers the exposure of polar functionalities by disrupting interfacial equilibrium and driving surface reconstruction. This reversible adaptation is governed by the dynamics of a metal–ligand coordinated polymer, and therefore can be easily tailored by the choice of network structure, metal cations, and counter anions. PDMS is a particularly exciting polymer for this functionality because of the negative consequences of its intrinsically high hydrophobicity in many applications. However, this design concept is applicable to a wide range of polymers and can be expanded to other dynamic interactions such as reversible covalent bonding, hydrogen bonding, and ionic bonding, to empower programmable responsive functionality and therefore enhance material performance. [ABSTRACT FROM AUTHOR]

Nanocomposite hydrogels consist of polymeric network embedded with functional nanoparticles or nanostructures, which not only contribute to the enhanced mechanical properties but also exhibit the bioactivities for regulating cell behavior. Bisphosphonates (BPs) are capable of coordinating with various metal ions and modulating bone homeostasis. Thanks to the inherent dynamic properties of metal–ligand coordination bonds, BP-based nanocomposite hydrogels possess tunable mechanical properties, highly dynamic structures, and the capability to mediate controlled release of encapsulated therapeutic agents, thereby making them highly versatile for various biomedical applications. This review presents the comprehensive overview of recent developments in BP-based nanocomposite hydrogels with an emphasis on the properties of embedded nanoparticles (NPs) and interactions between hydrogel network and NPs. Furthermore, various challenges in the biomedical applications of these hydrogels are discussed to provide an outlook of potential clinical translation.

Since triboelectrification results from materials in physical contact, the durability of triboelectric nanogenerators (TENGs) must be improved. However, it still poses challenges to continuously repair surface abrasion even when self‐healable materials are introduced. In this study, an ultrastretchable TENG (US‐TENG) that simultaneously heal the fracture and abrasion at room temperature is fabricated. By incorporating hydrogen bonds and dynamic metal‐ligand coordination into polydimethylsiloxane chains, the synthesized elastomers possess ultrahigh stretchability (10 000%) and remarkable self‐healing property (100% efficiency) at room temperature. Working in contact‐separation mode, the electrical outputs with 2 × 2 cm2 area can reach 140 V, 40 nC, 1.5 µA, respectively. Besides, the US‐TENG shows a stretchability of 1800% with high electrical outputs. Even if it is stretched to break or scratched to wear out, it can recover its electrical outputs in 20 min and 2 h at room temperature, respectively. Finally, the application of the US‐TENG as flexible power sources and self‐powered pressure sensors is demonstrated. This designed strategy with ultrahigh stretchability and excellent self‐healing properties can meet the wide applications of flexible and wearable electronics for long‐term use. [ABSTRACT FROM AUTHOR]

Ligand‐coordinated supported catalysts (LCSCs) are of growing interest for heterogeneous single‐atom catalysis. Here, the effect of the choice of organic ligand on the activity and stability of TiO2‐supported single‐atom Pt‐ligand catalysts was investigated for ethylene hydrogenation. The activity of these catalysts showed a significant dependence on the choice of ligand and also correlated with coordination number for Pt−ligand and Pt−Cl−. Of the three ligands examined in this study, the one with the lowest Pt coordination number, 1,10‐phenanthroline‐5,6‐dione (PDO), showed the lowest reaction temperature and highest reaction rate, likely due to those metal sites being more accessible to reactant adsorption. In‐situ X‐ray absorption spectroscopy (XAS) experiments showed that the activity also correlated with good heterolytic dissociation of hydrogen, which was supported by OH/OD exchange experiments and was the rate‐determining step of the hydrogenation reaction. In these in‐situ XAS experiments up to 190 °C, the supported Pt‐ligand catalyst showed excellent stability against structural and chemical change. Instead of Pt, the PDO ligand could be coordinated with Ir on TiO2 to form Ir LCSCs that showed slow activation by loss of Ir−Cl bonds, then excellent stability in the hydrogenation of ethylene. These results provide the chance to engineer ligand‐coordinated supported catalysts at the single‐atom catalyst level by the choice of ligand and enable new applications at relatively high temperature. [ABSTRACT FROM AUTHOR]

In this work, metal-ligand coordination interaction was utilized to induce the dynamic vulcanization (DV) of styrene-acrylonitrile copolymer (SAN)/butadiene acrylonitrile rubber (NBR)/cupric sulfate (CuSO 4) TPVs. The TPVs exhibited co-continuous structure, in which the CuSO 4 particles distributed in continuous NBR network to cross-link NBR phase through interaction between Cu2+ and nitrile groups (-CN), enhancing the mechanical strength and thickness of NBR network. CuSO 4 particles were refined to nanoparticles during DV, and then migrated to SAN/NBR interface and interacted with SAN and NBR simultaneously to realize in-situ compatibilization, resulting in efficient toughening of SAN without sacrificing its stiffness. With 20 phr CuSO 4 , the TPVs showed excellent impact toughness of 104.51 kJ/m2, which was 58 times that of the neat SAN. Meanwhile, the TPVs exhibited improved tensile strength, elongation at break, tensile toughness and Young's modulus, revealing the balanced stiffness-toughness properties of TPVs. We propose a feasible approach to fabricate high-performance TPVs, and it may expand the research scope of dynamic vulcanization. [Display omitted] • Metal coordination was innovatively utilized to initiate dynamic vulcanization. • CuSO 4 acted as curing agent to cure the NBR continuous network. • CuSO 4 acted as nano-sized compatibilizer to realize interfacial compatibilization. • The composites exhibited balanced stiffness-toughness properties. [ABSTRACT FROM AUTHOR]

At this time, the development of advanced elastic dielectric materials for use in organic devices, particularly in organic field-effect transistors, is of considerable interest to the scientific community. In the present work, flexible poly(dimethylsiloxane) (PDMS) specimens cross-linked by means of ZnCl2-bipyridine coordination with an addition of 0.001 wt. %, 0.0025 wt. %, 0.005 wt. %, 0.04 wt. %, 0.2 wt. %, and 0.4 wt. % of gold nanoparticles (AuNPs) were prepared in order to understand the effect of AuNPs on the electrical properties of the composite materials formed. The broadband dielectric spectroscopy measurements revealed one order of magnitude decrease in loss tangent, compared to the coordinated system, upon an introduction of 0.001 wt. % of AuNPs into the polymeric matrix. An introduction of AuNPs causes damping of conductivity within the low-temperature range investigated. These effects can be explained as a result of trapping the Cl− counter ions by the nanoparticles. The study has shown that even a very low concentration of AuNPs (0.001 wt. %) still brings about effective trapping of Cl− counter anions, therefore improving the dielectric properties of the investigated systems. The modification proposed reveals new perspectives for using AuNPs in polymers cross-linked by metal-ligand coordination systems.

Abstract Recent research has built a consensus that the binder plays a key role in the performance of high‐capacity silicon anodes in lithium‐ion batteries. These anodes necessitate the use of a binder to maintain the electrode integrity during the immense volume change of silicon during cycling. Here, Zn2+–imidazole coordination crosslinks that are formed to carboxymethyl cellulose backbones in situ during electrode fabrication are reported. The recoverable nature of Zn2+–imidazole coordination bonds and the flexibility of the poly(ethylene glycol) chains are jointly responsible for the high elasticity of the binder network. The high elasticity tightens interparticle contacts and sustains the electrode integrity, both of which are beneficial for long‐term cyclability. These electrodes, with their commercial levels of areal capacities, exhibit superior cycle life in full‐cells paired with LiNi0.8Co0.15Al0.05O2 cathodes. The present study underlines the importance of highly reversible metal ion‐ligand coordination chemistries for binders intended for high capacity alloying‐based electrodes.

Recent research has built a consensus that the binder plays a key role in the performance of high‐capacity silicon anodes in lithium‐ion batteries. These anodes necessitate the use of a binder to maintain the electrode integrity during the immense volume change of silicon during cycling. Here, Zn2+–imidazole coordination crosslinks that are formed to carboxymethyl cellulose backbones in situ during electrode fabrication are reported. The recoverable nature of Zn2+–imidazole coordination bonds and the flexibility of the poly(ethylene glycol) chains are jointly responsible for the high elasticity of the binder network. The high elasticity tightens interparticle contacts and sustains the electrode integrity, both of which are beneficial for long‐term cyclability. These electrodes, with their commercial levels of areal capacities, exhibit superior cycle life in full‐cells paired with LiNi0.8Co0.15Al0.05O2 cathodes. The present study underlines the importance of highly reversible metal ion‐ligand coordination chemistries for binders intended for high capacity alloying‐based electrodes. [ABSTRACT FROM AUTHOR]

The backbone of diketopyrrolopyrrole‐thiophene‐vinylene‐thiophene‐based polymer semiconductors (PSCs) is modified with pyridine (Py) or bipyridine ligands to complex Fe(II) metal centers, allowing the metal–ligand complexes to act as mechanophores and dynamically crosslink the polymer chains. Mono‐ and bi‐dentate ligands are observed to exhibit different degrees of bond strengths, which subsequently affect the mechanical properties of these Wolf‐type‐II metallopolymers. The counter ion also plays a crucial role, as it is observed that Py‐Fe mechanophores with non‐coordinating BPh4– counter ions (Py‐FeB) exhibit better thin film ductility with lower elastic modulus, as compared to the coordinating chloro ligands (Py‐FeC). Interestingly, besides mechanical robustness, the electrical charge carrier mobility can also be enhanced concurrently when incorporating Py‐FeB mechanophores in PSCs. This is a unique observation among stretchable PSCs, especially that most reports to date describe a decreased mobility when the stretchability is improved. Next, it is determined that improvements to both mobility and stretchability are correlated to the solid‐state molecular ordering and dynamics of coordination bonds under strain, as elucidated via techniques of grazing‐incidence X‐ray diffraction and X‐ray absorption spectroscopy techniques, respectively. This study provides a viable approach to enhance both the mechanical and the electronic performance of polymer‐based soft devices. [ABSTRACT FROM AUTHOR]

Materials exhibiting reversible changes of their photoluminescence properties upon exposure to heat have an immense potential in various advanced photonic applications. Particularly, the control over an on‐demand response of thermochromic luminescent materials (TLMs) similar to a chameleon is of great importance. However, it is still difficult and challenging to achieve it. Therefore, this paper reports a simple and effective way to construct TLMs, which involves the incorporation of the metal–ligand complexes into polyethylene glycol (PEG). Ratiometric or off–on response modes of these TLMs can be tuned by incorporating metal complexes based on either Zn2+ or Co2+ into PEG and by taking advantage of reversible metal–ligand coordination, dissociation, or excited‐state conformation changes of the resulting materials. Moreover, by choosing PEG matrices with different molecular weights, the thermochromic transition temperatures of these TLMs can be tuned. It is also demonstrated that the controllable response behavior of these chameleon‐like TLMs can be used in applications related to real‐life anti‐counterfeiting and security printing. This work opens novel opportunities for the development of smart materials with controllable responses useful for advanced photonic applications. [ABSTRACT FROM AUTHOR]

In this study, a supramolecular hydrogel formed by incorporating the 2,6‐bis(1,2,3‐triazol‐4‐yl)‐pyridine (btp) ligand in the backbone of a polymer prepared by copper(I)‐catalyzed alkyne‐azide cycloaddition (CuAAC) "click" polyaddition reaction of 2,6‐diethynylpyridine and diazido‐poly(ethylene glycol) is reported. The hydrogelation is selectively triggered by the addition of Ni2+ ions to aqueous copolymer solutions. The gelation and rheological properties could be tuned by the change of metal to ligand ratio and polymer concentration. Interestingly, the hydrogel exhibits a fast (within 2 min) and excellent repeatable autonomic healing capacity without external stimuli. This self‐healing behavior may find potential applications for the repairing of metal coatings, in the future. [ABSTRACT FROM AUTHOR]

The effect of metal-ligand coordination on crystallization and melting behaviors of polymers has not been comprehensively investigated. In this study, a series of supramolecular poly(l -lactic acid)s (SM-PLLAs) were prepared by changing various metal ions, length of polymer chains and stoichiometric ratio of ligands to metal ions (L/M). The complexation of metal ions with ligands in SM-PLLAs was confirmed by the intrinsic viscosity and UV–visible spectroscopy. It was found that crystallization rate and crystallinity of SM-PLLAs were strongly dependent on the chain length of precursor in both non-isothermal and isothermal crystallizations. With chain length of 1.6 kg/mol, crystallization of PLLA was completely suppressed regardless of the metal ions, whereas PLLA with longer chain length of 3.0 kg/mol exhibited strong dependence of the type of metal. During the heating process, melting behaviors can be tuned by the strength of metal-ligand coordination, temperature and the degree of complexation. Unlike PLLA precursor and SM-PLLA coordinated with Cu2+ exhibited multiple melting behaviors, only a single melting peak was appeared in PLLA bonded with Co2+, indicative of suppression of recrystallization during heating. With ratio of ligand to Co2+ increased from 1:1 to 6:1, crystallization and melting behaviors were tuned by the content of free and bounded PLLA chains. As compared to Cu2+, SM-PLLA coordinated with Co2+ exhibited higher complex modulus and viscosity due to the high bond strength, as well as a more stable structure underwent heating and shear, making diffusion of polymer chains and the structural adjustment more difficult. This work may shed light on understanding the intricate interplay of metal-ligand coordination effects on the crystallization and melting behaviors of polymers, which may be helpful with the design and making out the relationship between structure and properties of supramolecular polymers. The influence of metal-ligand coordination on the crystallization and melting behaviors of PLLA were investigated. Crystallization kinetics were dependent on the chain length of polymers, bond strengths and the ratios of ligands to metal ions. Most of SM-PLLAs exhibited multiple melting behaviors, whereas SM-PLLA coordinated with Co2+ showed a single melting peak. [Display omitted] • The influence of metal-ligand coordination on the crystallization and melting behaviors of PLLA was investigated. • Crystallization kinetics were dependent on the chain length of PLLA, type of metal ions and the ratio of L/M. • SM-PLLA coordinated with Co2+ showed one single melting peak, indicative of hinderance of recrystallization process. • As compared with Cu2+, SM-PLLA bonded with Co2+ had a more stable structure, higher viscosity and complex modulus. [ABSTRACT FROM AUTHOR]

Nanocellulose-based hydrogels have attracted increasingly attention due to their biocompatibility, biodegradability, and hydrophilic properties. In this work, we proposed a simple route to fabricate composite hydrogels using TEMPO oxidized cellulose nanofibrils (TOCNF) and tannin through metal-ligand coordination. Calcium ions were utilized to rapidly cross-link the carboxyl groups on TOCNF and the tannins' catechol moieties via metal-ligand bonding, resulting in the formation of TOCNF-Ca2+-T composite hydrogels. The incorporation of tannins endowed the hydrogel with high antioxidant and antibacterial properties. The rheological analysis revealed that the addition of tannin led to an improved gel strength of the composite hydrogel. The hydrogel was injectable and could autonomously self-healed in 1 min without any trigger. Tetracycline hydrochloride (TH) was successfully loaded into the composite hydrogels, achieving a maximum encapsulation rate of 97.32%. TOCNF-Ca2+-40%T demonstrated a cumulative drug release of 36% at pH 1.3 and 86% at pH 7.4, indicating its pH-responsive nature. These hydrogels, derived from plant sources, exhibited high antibacterial and antioxidant properties, as well as biocompatibility, rapid self-healing, and injectability, which open up new possibilities for applications in wound dressing and drug delivery. [Display omitted] • Hydrogels were fabricated using TOCNF and tannin via metal-ligand coordinate bonds. • TOCNF-Ca2+-T hydrogels exhibited high antioxidant and antibacterial properties. • The hydrogel was injectable and could autonomously self-healed in 1 min. • The composite hydrogels are suitable for use in wound dressing and drug delivery. [ABSTRACT FROM AUTHOR]

Developing polymeric materials with remarkable mechanical properties and fast self-healing performance even at low temperatures is challenging. Herein, the polymeric nanocomposites containing silane-treated cellulose nanocrystals (SCNC) with ultrafast self-healing and exceptional mechanical characteristics were developed even at low temperatures. First, CNC is modified with a cyclic silane coupling agent using an eco-friendly chemical vapor deposition method. The nanocomposite was then fabricated by blending SCNC with matrix prepolymer, prepared from monomers that possess lower critical solution temperature, followed by the inclusion of dibutyltin dilaurate and hexamethylene diisocyanate. The self-healing capability of the novel SCNC/polymer nanocomposites was enhanced remarkably by increasing the content of SCNC (0–3 wt%) and reaching (≥99 %) at temperatures (5 & 25 °C) within <20 min. Moreover, SCNC-3 showed a toughness of (2498 MJ/m3) and SCNC-5 displayed a robust tensile strength of (22.94 ± 0.4 MPa) whereas SCNC-0 exhibited a lower tensile strength (7.4 ± 03 MPa) and toughness of (958 MJ/m3). Additionally, the nanocomposites retain their original mechanical properties after healing at temperatures (5 & 25 °C) owing to the formation of hydrogen bonds via incorporation of the SCNC. These novel SCNC-based self-healable nanocomposites with tunable mechanical properties offer novel insight into preparing damage and temperature-responsive flexible and wearable devices. [Display omitted] [ABSTRACT FROM AUTHOR]

Hydrogels that have both permanent chemical crosslinks and transient physical crosslinks are good model systems to represent tough gels. Such “dual-crosslink” hydrogels can be prepared either by simultaneous polymerization and dual crosslinking (one-pot synthesis) or by diffusion/complexation of the physical crosslinks to the chemical network (diffusion method). To study the effects of the preparation methods and of the crosslinking ratio on the mechanical properties, the equilibrium swelling of the dual-crosslink gels need to be examined. Since most of these gels are polyelectrolytes, their swelling properties are complex, so no systematic study has been reported. In this work, we synthesized model dual-crosslink gels with metal–ligand coordination bonds as physical crosslinks by both methods, and we proposed a simple way of adding salt to control the swelling ratio prepared by ion diffusion. Tensile and linear rheological tests of the gels at the same swelling ratio showed that during the one-pot synthesis, free radical polymerization was affected by the transition metal ions used as physical crosslinkers, while the presence of electrostatic interactions did not affect the role of the metal complexes on the mechanical properties.

Many living organisms have amazing control over their color, shape, and morphology for camouflage, communication, and even reproduction in response to interplay between environmental stimuli. Such interesting phenomena inspire scientists to develop smart soft actuators/robotics via integrating color‐changing functionality based on polymer films or elastomers. However, there has been no significant progress in synergistic color‐changing and shape‐morphing capabilities of life‐like material systems such as hydrogels. Herein, we reported a new class of bioinspired synergistic fluorescence‐color‐switchable polymeric hydrogel actuators based on supramolecular dynamic metal–ligand coordination. Artificial hydrogel apricot flowers and chameleons have been fabricated for the first time, in which simultaneous color‐changing and shape‐morphing behaviors are controlled by the subtle interplay between acidity/alkalinity, metal ions, and temperature. This work has made color‐changeable soft machines accessible and is expected to hold wide potential applications in biomimetic soft robotics, biological sensors, and camouflage. [ABSTRACT FROM AUTHOR]

Recently, metal coordination has been widely utilized to fabricate high‐performance hydrogels, but conventional metal‐based hydrogels face some drawbacks, such as staining or acid lability. In the present study, a novel kind of colorless Zr(IV)‐crosslinked polyacrylamide/polyanionic cellulose (PAM/PAC) composite hydrogel with unique acid resistance was constructed via acrylamide polymerization in a PAC solution, followed by posttreatment in a zirconium oxychloride (ZrOCl2) solution. The prepared gels were characterized in terms of Fourier transform infrared spectroscopy, scanning electron microscopy, and tensile and compressive mechanics, as well as acid resistance. Inside the gels, the synergistic action of hydrogen bonding and Zr(IV) coordination is responsible for their improved mechanical properties and good energy dissipation ability. One hydrogel with nearly 90 wt % of water content can sustain approximately 5 MPa of compression stress at 90% strain without damage. Both microscopic network structures and macroscopic mechanics demonstrate facile adjustability via changing the PAC dosages in polymerization and/or ZrOCl2 concentrations in posttreatment. Moreover, the gels present unexpected acid resistance due to the strong Zr(IV) coordination with PAC, demonstrating their potential application as hydrogel electrolytes in supercapacitors. The current work provides a new approach to fabricate metal coordination‐based high strength, colorless hydrogels with acid resistance. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 981–991 [ABSTRACT FROM AUTHOR]

DFT/B3LYP calculations with full geometry optimizations have been carried out on 1-phenylazo-2-naphthol and their metal complexes of formula M(MePhNap)2 (M = Ni, Pd, Pt, Cu, Ag, and MePhNap = 1-(− 4-methylphenylazo)-2-naphtol) in their neutral, oxidized, and reduced forms. The predicted structures provide to the M(II) metal ions the square planar geometry and distorted azo ligand. The TD-DFT theoretical study performed on the optimized geometry allowed us to predict the UV–Vis spectra and to identify quite clearly the spectral position and the nature of the different electronic transitions according to their molecular orbital localization. Large HOMO-LUMO gaps are calculated for all optimized structures suggesting good chemical stabilities, hence, reproducing the available UV–Vis spectra and compared to that of free ligand. The electronic spectra obtained in DMSO and ethanol polar solvents predict more important red shifts than those obtained in hexane as nonpolar one. [ABSTRACT FROM AUTHOR]

A series of porphyrin triads (1–4), in which each triad is composed of a Sn(IV) porphyrin and two free-base (or Zn(II)) porphyrins, was synthesized and their self-assembled nanostructures were studied. Depending on the substituent on porphyrin moieties, each triad was self-assembled into a different nanostructure. In particular, the cooperative coordination of 3-pyridyl groups in the Sn(IV) porphyrin with the axial Zn(II) porphyrins in triad 4 leads to forming uniform nanofibers with an average width of 10–22 nm. Other triads without the coordinating interaction between the central Sn(IV) porphyrin and the axial porphyrins formed irregularly shaped aggregates in contrast. The morphologies of nanofiber changed drastically upon the addition of pyrrolidine, in which pyrrolidine molecules break down the self-assembly process by coordinating with the axial Zn(II) porphyrins. All porphyrin aggregates exhibited efficient photocatalytic performances on the degradation of methylene blue dye under visible light irradiation. The degradation efficiencies after 2 h were observed to be between 70% and 95% for the aggregates derived from the four triads.

Two gluconic acid derivatives C3 and C6 bearing a terpyridyl moiety were designed and synthesized. Thanks to the hydrophilic interaction from glucosyl moiety, C3 and C6 can dissolve in polar solvents and gel aromatic solvents with a critical gel concentration of weight 1.5%. The solution consisting of organic ligand C3 as sensitizer and Ln (III) ions as emitters can realize white light emission with thermo- and chemical stimuli-response properties in luminescence spectra. Further, the self-assemblies of C3 and C6 were examined by the combination of the theoretical calculations via hybrid density functional theory (DFT) with 1 H nuclear magnetic resonance ( 1 HNMR) and powder X-ray diffraction (PXRD) analysis. The study actually provides a reliable method for the formation of potential functional smart materials. [ABSTRACT FROM AUTHOR]

Abstract: In this study, metallo‐supramolecular polyesters with multiple coordination bonds along the chains are prepared, to demonstrate a simple strategy to control both the thermal property and crystallizability. Firstly, polyesters with multiple pyridine‐ligands are synthesized through melt polycondensation and subsequent Michael addition reaction. By adding a metal salt (ZnCl2), the fraction of metal‐coordinated pyridine‐ligands is systematically increased with increasing the Zn2+/pyridine‐ligands mole ratio according to Fourier transform infrared spectroscopy (FT‐IR) measurements, which is found to play a role in tuning the glass transition temperature. The metal‐ligand coordination simultaneously causes the disappearance of crystallization/melting peaks in differential scanning calorimetry (DSC) thermograms, and scattering measurements also indicate the disappearance of crystalline domains. A transparent film is thus obtained after blending small amounts of ZnCl2 (≪10 wt%), although the neat crystalline sample is highly opaque. This non‐crystallization phenomenon is induced by inhibition of the chain arrangement due to the existence of metal salts dispersed via coordination with pyridine‐ligands. By changing the fraction of pyridine‐ligands in the chain, it is found that the wider temperature range Tg tuning can be achieved for samples with higher ligand fractions. [ABSTRACT FROM AUTHOR]

Coordination-driven self-assembly strategy has demonstrated the efficiency and versatility to construct well-ordered supramolecular coordination complexes (SCCs) such as discrete metallacycles and metallacages. In recent years, it has aroused tremendous interest to build more complexed self-assembled structures via the implementation of additional non-covalent recognition motifs on the SCCs platform. In this work, we have successfully attained this objective, with the elaborate manipulation of non-interfering pyridine-Pt and molecular tweezer/guest complexation in a hierarchical self-assembly manner. The resulting SCCs-based linear supramolecular polymers exhibit intriguing NIR-emissive behaviors, primarily attributed to the presence of intermolecular Pt(II)-Pt(II) metal-metal interactions in the non-covalent tweezering structure. Hence, supramolecular engineering of multiple non-covalent interactions offers a feasible avenue toward functional materials with tailored properties. [ABSTRACT FROM AUTHOR]

Nowadays, it is still a challenge to prepare flexible sensors with great mechanical strength, stretchability, high sensitivities, and excellent self-healing (SH) abilities. Herein, a nanostructured supramolecular elastomer is reported with a dual noncovalent network of hydrogen bonding interactions and metal-ligand coordination. The resultant flexible sensor presents ultrafast (30 s), autonomous, and repeatable SH ability with high healing efficiency (80% after the 3rd healing process), as well as enhanced mechanical properties. Benefitting from the 3D conductive network, the sensor exhibits high electrical sensitivity and very low detection limit (0.2% strain). As a result, the flexible sensor is capable of precisely monitoring small strains of human motions (such as vocal-cord vibration), and exhibits reproducible and recognizable current signals after cutting-healing process. The dual noncovalent network design proposed here opens up a new opportunity for scalable fabrication of high performance SH sensors and other electronic devices. [ABSTRACT FROM AUTHOR]

Double-shelled hollow (DSH) structures with varied inorganic compositions are confirmed to have improved performances in diverse applications, especially in lithium ion battery. However, it is still of great challenge to obtain these complex nanostructures with traditional hard templates and solution-based route. Here we report an innovative pathway for the preparation of the DSH nanospheres based on block copolymer self-assembly, metal−ligand coordination and atomic layer deposition. Polymeric composite micelles derived from amphiphilic block copolymers and ferric ions were prepared with heating-enabled micellization and metal−ligand coordination. The DSH nanospheres with Fe2O3 stands inner and TiO2 outer the structures can be obtained with atomic layer deposition of a thin layer of TiO2 followed with calcination in air. The coordination was carried out at room temperature and the deposition was performed at the low temperature of 80 °C, thus providing a feasible fabrication strategy for DSH structures without destruction of the templates. The cavity and the outer layer of the structures can also be simply tuned with the utilized block copolymers and the deposition cycles. These DSH inorganic nanospheres are expected to find vital applications in battery, catalysis, sensing and drug delivery, etc.

The self-healing property based on metal-ligand physical coordination is particularly interesting in bio-hydrogel science due to its allowance for multiple local healing events to process. As the most abundant renewable green resource in nature, Gleditsia sinensis galactomannan has great potential as a starting material for functional materials. In this study, the biocompatible Gleditsia sinensis galactomannan and cellulose were firstly chemically modified and then taken as the main constituent for constructing the metal-ligand coordination through an enzyme-regulated strategy. The hydrogel could quickly gelatinize in the surrounding environment, corresponding to the violent exothermic phenomenon, and exhibit extraordinary self-healing behavior. The molecular dynamics simulation of the hydrogel confirmed the more stable coordinated configuration from Fe(III)-chelates than Fe(II)-chelates. The morphology, mechanical property, antibacterial, and cytotoxicity of the prepared hydrogel were also studied. Our results indicated that galactomannan hydrogel based on the metal-ligand networks could balance the kinetic stability and intrinsic healability through the enzyme-induced route, which provide a new perspective in the field of biomaterial applications. • Polysaccharide is a green and nontoxicity food-grade materials • A dual-network self-repairing hydrogel was developed via an enzyme-induced route to accelerate the synthetic process • The novel polysaccharide-based hydrogel based on metal-ligand networks possess self-healing and antibacterial properties • The hierarchical strategy for metal-ligand networks balanced the kinetic stability and intrinsic healability [ABSTRACT FROM AUTHOR]

Proteins, as the premier building blocks in nature, exhibit extraordinary ability in life activities during which process proteins mostly self-assemble into large complexes to exert prominent functions. Inspired by this, recent chemical and biological studies mainly focus on supramolecular self-assembly of proteins into high ordered architectures, especially the assembly strategy to unravel the formation and function of protein nanostructures. In this review, we summarize the progress made in the engineering of supramolecular protein architectures according to the strategies used to control the orientation and the order of the assembly process. Furthermore, potential applications in biomedical areas of the supramolecular protein nanostructures will also be reviewed. [ABSTRACT FROM AUTHOR]

• Formed smart multicolor fluorescent cellulose hydrogels with antibacterial activity. • The hydrogel layer shrinks/swells in alkaline/acidic solutions. • Achieved synergetic color-changing and shape-morphing via single external stimulus. • Developed an intelligent octopus-shaped soft robot with camouflaging capability. The development of stimulus-responsive materials with multifunctionality is important for achieving bionic artificial intelligence. However, stimulus-responsive cellulose hydrogels that simultaneously change their shape and fluorescent color under a single stimulus are difficult to fabricate. Here smart, multicolor fluorescent cellulose hydrogels were prepared from cellulose, levofloxacin, epichlorohydrin, and lanthanide ions (Eu3+ or Tb3+). The hydrogels were incorporated with pan paper into synergetic color-changing and shape-morphing actuators (Eu-CLF and Tb-CLF actuators). Besides fluorescing with the metal ligands, levofloxacin possesses antibacterial activity. The fluorescence color of Eu-CLF hydrogel in Tb3+ solution changed from red to yellow, whereas that of Tb-CLF hydrogel in Eu3+ solution changed from green to red. Both the Eu-CLF and Tb-CLF hydrogels fluoresced blue and green in alkali and acid solution, respectively. The actuator thus achieves synergetic color-changing and shape-morphing under a single external stimulus (acidic/alkaline switching). Such an activator shaped like a bionic flower and an intelligent octopus-type soft robot with camouflaging ability were then prepared. This study provides an elegant strategy for developing advanced multi-responsive multicolor tunable behaviors for bionic soft robots, biosensors, and camouflaged robots. [ABSTRACT FROM AUTHOR]

[Display omitted] • The amino acid P(AM-HisMA) hydrogels and P(AM-HisMA)-Fe3+ hydrogels exhibited ultra-stretchability, stable resistance, good adhesion, and excellent mechanical properties. • By introducing FeCl 3 , the P(AM-HisMA)-Fe3+ hydrogel resulted in better mechanical properties, shorter self-healing time, and stronger tissue adhesion strength. • The P(AM-HisMA)-Fe3+ hydrogel showed remarkable biocompatibility and excellent antibacterial property (100 % killing ratio). • The P(AM-HisMA)-Fe3+ hydrogel accelerated the wound healing process. • The P(AM-HisMA)-Fe3+ hydrogels could be used as sensors to monitor human motions. It is a great challenge to prepare hydrogels with tissue adhesion, ultra-stretchability, and good tensile stress as wound dressings. Here, we reported a poly(acrylamide-histidine methacrylamide) (P(AM-HisMA)) hydrogel polymerized by histidine methacrylamide (HisMA) as a biocompatible amino acid derivative and acrylamide (AM). Since the amino acid HisMA provided physical cross-linking to the P(AM-HisMA) hydrogel, the hydrogel had self-healing properties (tensile strength recovery > 84 %), adhesion (4.1 kPa for porcine skin), and excellent mechanical properties (tensile stress of 77 kPa, tensile elongation of 5800 %, compressive stress of 2.0 MPa) when compared with polyacrylamide (PAM) hydrogels. Moreover, we prepared the P(AM-HisMA)-Fe3+ hydrogel by immersing Fe3+ ions into the P(AM-HisMA) hydrogel. The hydrogel contained histidine-Fe3+ coordination bonds and various non-covalent bonds, which resulted in better physical properties such as reinforced mechanical property (tensile strength of 89 kPa, stretchability of 4900 %), enhanced adhesive strength (11.9 kPa for porcine skin), and better self-healing property (within 5 min). The P(AM-HisMA)-Fe3+ hydrogel showed remarkable biocompatibility and excellent antibacterial property (100 % killing ratio). In vitro wound healing experiments demonstrated that P(AM-HisMA)-Fe3+ hydrogel effectively accelerated the wound healing process. Furthermore, the P(AM-HisMA)-Fe3+ hydrogels have promising application prospects as dressing materials for joint skin wound healing. [ABSTRACT FROM AUTHOR]

The ability to repair rapidly is extremely important for self-healing elastomers in practical applications. Here, we fabricate a fast self-healing polyurethane with enhanced mechanical properties by introducing Cu-pyridine coordination in the hard segments. The cupric ions coordinate with the pyridine groups, effectively increasing the hydrogen bonds between urea bonds. With the incremental coordination bonds and hydrogen bonds in hard segments, the mechanical properties of the polyurethane are improved while the soft segments still keep the good mobility. Combined with the strong photothermal effect of Cu-pyridine coordination, the healing speed of the elastomer is promoted greatly. As a result, the elastomer owns good tensile strength up to 5 MPa and fast self-healing properties (healing efficiency up to 53% in 30 s and 99% in 2 min after irradiation with a 785 nm laser). [Display omitted] • A synergetic method is proposed to design fast self-healing elastomer with enhanced mechanical properties. • Molecular design of only regulating hard segments via dynamic bonds to ensure good mobility of soft segments. • Cu-pyridine coordination endows the polyurethane with strong photothermal effect. • The polyurethane exhibits excellent fast self-healing ability and good mechanical properties. [ABSTRACT FROM AUTHOR]

In this review, supramolecular coordination processes on two-dimensional (2D) surfaces or interfaces observed by scanning tunneling microscopy (STM) are discussed. Four parts are mainly involved, which include (1) recognition of Fe3+ through functional molecular networks, (2) K+-induced switching of valinomycin, (3) supramolecular coordination happened in a nano-reactor, (4) reversible 2D supramolecular spring driven by coordination. The direct insight of the coordination phenomena provided by STM supplements our knowledge of its mechanism. Since different building blocks can be connected into a whole part through coordination, the understanding of its mechanism will be beneficial to the future design of molecular devices. [ABSTRACT FROM AUTHOR]

• Highly stretchable and self-healing materials based on metal–ligand coordination. • Choice of solvents can significantly affect the results of fabricated products. • SAXS/WAXS models constructed under different scenarios. • Robust skin-inspired pyramidal sensors can be performed over 100 cycles. Self-healing and stretchable materials have attracted considerable attention due their wide potential applications in developing human–machine interfaces. However, it remains a great challenge to achieve polymeric materials capable of both self-healing at room temperature and fast elastic recoverability after cuts or high stretching. We report herein a new material based on tolylene 2,4-diisocyanate elastomer (PTD) terminated with 4,4′-Bis(hydroxymethyl)-2,2′-bipyridine (bpy), having autonomously self-healing and ultra-fast stretching recovery properties, through incorporating trans -octahedral metal–ligand coordination of Zn2+ or Ni2+ ions with the bpy moieties; both Zn- and Ni-bpyPTD show combined properties of water-resistant, anti-bacteria, low toxicity and high transparency, and of respective emphases in self-healing and mechanical strength. The underlying mechanism is associated with the trans -octahedral metal–ligand coordination and their organized nanostructures as effective crosslinking sites in the bpyPTD matrix of rich hydrogen bonding, as revealed by X-ray absorption and in-situ small- and wide-angle X-ray scattering. Particularly, when fabricated into a pressure sensor, Ni-bpyPTD exhibits synchronized and durable mechanical and electrical responses under a repetitive cycling tensile testing up to 300% strain within 60 s, over 100 cycles, and would serve as a promising material for skin-inspired tactile sensing. [ABSTRACT FROM AUTHOR]

Novel hybrid diblock copolymers consisting of bidentate ligand-functionalized chains have been synthesized via click reaction and RAFT radical polymerization. The chemical structure and molecular weight of the synthesized poly(methacrylate-POSS)-block-poly(4-vinylbenzyl-2-pyridine-1H-1,2,3-triazole) (PMAPOSS-b-PVBPT) were characterized by NMR and GPC. The copolymers had been utilized to construct metal-containing polymer micelle by the metal–ligand coordination and electrostatic interaction in this study. The self-assembly behaviors of PMAPOSS-b-PVBPT in chloroform, a common solvent, under the effect of Zn(OTf)2 and HAuCl4 were investigated by TEM, DLS, and variable temperature NMR. Besides, micellization of this diblock copolymer was achieved in ethylene glycol, a selective solvent for PMAPOSS-b-PVBPT. The experimental results revealed that the incorporation of heterocyclic rings bearing nitrogen atoms in polymer side chains played an important role in the construction of metal-containing copolymer micelles. The prepared metal-containing PMAPOSS-b-PVBPT micelles had good dynamic and thermal stability due to the strong metal–ligand coordination interaction and electrostatic interaction. [ABSTRACT FROM AUTHOR]

A C2-symmetrical tetrakis(arylethynyl) cavitand was synthesized. Spontaneous formation of hybrid hydrogen bonded/metal-ligand coordination supramolecular capsules occurs upon mixing 1 with cis-coordinated Pt2+ or Pd2+ metal complexes. The hybrid supramolecular capsules encapsulated neutral guest molecules only in polar solvents. [ABSTRACT FROM AUTHOR]

Highlights: [•] Macromonomers bearing BTP ligand units and UPy motifs are synthesized. [•] Gels are constructed by orthogonal metal–ligand coordination and hydrogen bonding. [•] Gelation is influenced by the length of polymer linker between terminal UPy motifs. [•] Gels exhibit multi-responsive properties. [Copyright &y& Elsevier]

Abstract: A novel metal responsive organic–inorganic hybrid amphiphile with a well-defined cage structure bearing a hydrophobic polyhedral oligomeric silsesquioxane (POSS) head and a hydrophilic poly(ethylene glycol) tail functionalized with a bidendate ligand was synthesized via amidation and esterification reactions. The structure of the novel amphiphilic surfactant, aminopropylisooctyl–POSS–maleic acid-poly-(ethylene glycol)-dipicolinic acid (POSS–MA–PEG–DPA), was characterized by NMR, and its self-assembly behavior was investigated by transmission electron microscopy, dynamic light scattering, and UV–vis spectrophotometry. The experimental results revealed that the micelle morphology could be controlled by the addition of zinc ions. The proposed modulation mechanism involves the combination of hydrophobicity, metal coordination and repulsive interactions. Furthermore, the coordination bonds provide the micelles with good dynamic and thermal stability. We also found that the tadpole-shaped amphiphile could form reverse micelles with an average diameter of approximately 30nm. [Copyright &y& Elsevier]