Dynamic Imine Bonds Research Articles

PH and Magnetism Dual-Responsive Pickering Emulsion Stabilized by Dynamic Covalent Fe3O4 Nanoparticles.

Herein, we describe pH and magnetism dual-responsive liquid paraffin-in-water Pickering emulsion stabilized by dynamic covalent Fe3O4 (DC-Fe3O4) nanoparticles. On one hand, the Pickerinfigureg emulsions are sensitive to pH variations, and efficient demulsification can be achieved by regulating the pH between 10 and 2 within 30 min. The dynamic imine bond in DC-Fe3O4 can be reversibly formed and decomposed, resulting in a pH-controlled amphiphilicity. The Pickering emulsion can be reversibly switched between stable and unstable states by pH at least three times. On the other hand, the magnetic Fe3O4 core of DC-Fe3O4 allowed rapid separation of the oil droplets from Pickering emulsions under an external magnetic field within 40 s, which was a good extraction system for purifying the aqueous solution contaminated by rhodamine B. The dual responsiveness enables Pickering emulsions to have better control of their stability and to be applied more broadly.

High-performance epoxy vitrimer with superior self-healing, shape-memory, flame retardancy, and antibacterial properties based on multifunctional curing agent

The lack of functionalities such as degradability, antibacterial, and flame retardancy is the key to limit the further wide application of conventional epoxy thermosets. In this work, a novel bio-based multifunctional amine curing agent (named HVPA), was successfully synthesized via the Schiff base reaction between six-vanillin functionalized cyclophosphazene and N-methylethylenediamine. And an epoxy vitrimer (HVPA/GDE) was fabricated by utilizing HVPA to cure the bio-based epoxy of glycerol diglycidyl ether (GDE). Ascribing to the even distribution of dynamic imine bond in each crosslinking linkage, this synthetic HVPA/GDE vitrimer presented excellent comprehensive properties including fast self-healing (8 min for 100%, without any pressure), excellent shape memory, easy reprocessability (1.5 MPa, 3 min, 100 °C), mild degradation, and superior bacterial resistance to both Gram-negative bacteria (E. coli) and Gram-positive bacteria (S. aureus). Moreover, due to the high content of N/P elements and benzene groups within the network structure, this HVPA/GDE not only exhibited excellent flame retardancy but also possessed good UV resistance and transparency, while maintaining comparable mechanical strength compared to the control group of commercial amine curing agent 4,4-Diaminodiphenyl methane (DDM) cured epoxy resin (DDM/GDE). Therefore, this work provides a facile strategy for fabricating multi-functional and high-performance bio-based epoxy resins.

Fast Self-Healing and Self-Cleaning Anticorrosion Coating Based on Dynamic Reversible Imine and Multiple Hydrogen Bonds

Anticorrosive coatings are extensively investigated as a potential solution to prevent or at least retard metal corrosion occurrence. However, the actual breakthrough is still hampered by the risk of barrier properties loss because of the local failure of the coating. Self-healing coatings can effectively repair microcracks, but outstanding self-healing behavior is always accompanied by poor self-cleaning ability. Herein, we report a series of poly(dimethylsiloxane) (PDMS) modified with a terephthalic aldehyde (TA)-polyurea (PDMS-TA-PUa) copolymer with a double reversible dynamic bond crosslinking network structure. The PDMS-TA-PUa coating exhibits fast and re-recycled self-healing behavior that heals cracks within 40–50 min at room temperature. The fast self-healing property is attributed to the dynamic nature of the imine bonds and hydrogen bonds in polymer networks. The PDMS-TA-PUa coating also shows great self-cleaning and anticorrosive ability, due to high hydrophobic, low surface energy, and high corrosion potential. Our work gives an insight into the design and preparation of multifunctional coating material with excellent anticorrosion performance, fast self-healing, and self-cleaning properties.

Bacterial responsive hydrogels based on quaternized chitosan and GQDs-ε-PL for chemo-photothermal synergistic anti-infection in diabetic wounds

Clinically, systemic antibiotic therapy and traditional dressings care are not satisfactory in treating chronic diabetic ulcers (DU). Therefore, we presented sprayable antibacterial hydrogel for effective treatment of DU by using antibacterial macromolecules (quaternized chitosan, QCS, Mn ≈ 1.5 × 105), photothermal antibacterial nanoparticles (ε-poly-l-lysine grafted graphene quantum dots, GQDs-ε-PL) and miocompatible macromolecules (benzaldehyde-terminated four-arm poly(ethylene glycol), 4 arm PEG-BA) as materials. The results revealed that the hydrogel could be in situ formed in 70–89 s through dynamic imine bonds crosslinking and exhibited a pH-dependent swelling ability and degradability. The hydrogel could respond to bacterial triggered acidic environment to play a synergistic effect of chemotherapy and xenon light irradiated PTT, leading to the rupture of the bacterial membrane and the inactivation of bacteria, promoting the migration and proliferation of fibroblast cell, enhancing the adhesion of platelet endothelial cell, and finally accelerating the healing of infected diabetic wound. Moreover, the hydrogel displayed self-healing, hemostatic, and biocompatible abilities, which could provide a better healing environment for wound and further promote wound healing. Hence, the multifunctional hydrogel is expected to be a potential dressing for the clinical treatment of DU.

Thermo-processable chitosan-based plastic substitute with self-adaptiveness and closed-loop recyclability

The increasing environmental burden generated by disposable plastic wastes makes the development of sustainable substitute materials an emergent task. As one of the most abundant bioresources, chitosan (CS) has been considered as a potential candidate for plastic substitution. Conventionally, CS-based materials are fabricated through a solution-processing procedure due to the high crystallinity of CS. Herein, we designed a CS-based material via integrating CS into the network of polyimine (PI), which shows thermomechanical processability similar to plastics. Strong interactions were achieved through dynamic imine bond and hydrogen bond and thus formed a thermo-processable dynamic composite network. These CS-based plastic substitutes exhibit exceptional mechanical performances, excellent thermal/chemical stability, and a series of self-adaptiveness, including re-healing, reprocessing and multi-layer laminating. Notably, CPs can be easily degraded and 100% recycled for the production of next-generation materials. This work provides an alternative route to produce green and sustainable biomass materials as a plastic substitute.

Reversible polymerization of carbon dots based on dynamic covalent imine bond

Carbon dots (CDs), as new type of carbon-based nanoparticles, are considered to be an aggregate with irreversible polymerization. Achieving the reversible tunability of CDs luminescence based on their reversible polymerization is a challenging subject. Herein, we, for the first time, design and construct the blue-emitting CDs with reversible polymerization by a room-temperature Schiff base reaction between tannic acid and ethylenediamine. The formation of CDs is proven to be due to the crosslinking polymerization of precursors caused by imine bond. As a dynamic covalent bond, imine bond endows CDs with controllable structural transformation properties, and the prepared CDs can be depolymerized and polymerized reversibly by pH-controlled imine bond cleavage and re-formation. These properties of reversible fluorescence photoswitching make the CDs have a good application prospect in reversible information encryption.

2D Covalent Organic Frameworks with cem Topology.

A large number of covalent organic frameworks (COFs) with two-dimensional (2D) layered structures have been reported, but their network structures are restricted to only seven topologies (namely, hcb, hxl, kgm, sql, tth, bex, and kgd) because of the limited choice of building blocks. In this work, we illustrate how linking pseudo-fivefold symmetric 1,2,3,4,5-penta(4-formylphenyl)pyrrole with linear aromatic diamines through dynamic imine bonds produces three 2D porous COFs with an unprecedented cem topology, which represent the first examples of five-vertex semiregular Archimedean tessellations in COFs. The three 2D COFs are isostructural, and each adopts an eclipsed stacking structure with unidirectional hierarchical pores, in which the pyrrole unit is utilized as the five-vertex of network to form both square and triangular pores in a 33.42 sequence. With high thermal and chemical resistances, the COF-packed HPLC columns show excellent performance to provide separation of 10 different polycyclic aromatic hydrocarbons, a group of the most widespread organic environmental pollutants. The implementation of five-vertex Archimedean tessellations thus couriers a strategy to design COFs with new topologies and paves a new way to expand the inimitable properties of COF materials.

Highly conductive self-healing polymer electrolytes based on synergetic dynamic bonds for highly safe lithium metal batteries

Self-healing polymer electrolytes can improve the safety, reliability and cycle life of the batteries. Herein,we developed a self-healing polymer electrolyte (IBshPE) with high ionic conductivity and excellent self-healing property. IBshPE cross-linked by synergetic dynamic imine bond and boroxine bond was prepared via the reaction of 2-formylphenylboronic acid and poly(ethylene glycol) diamine. In IBshPE, boroxine bonds with B-N coordination and imine bonds can synchronously undergo fast bond exchange reactions, enabling rapid self-healing of IBshPE. IBshPE shows high self-healing efficiency of 97% within 4 h. The healed IBshPE has nearly the same mechanical property and ionic conductivity as the original IBshPE. IBshPE exhibits the highest ionic conductivity (5.08 × 10−3 S cm−1 at 30 °C) among the reported self-healing polymer electrolytes. IBshPE facilitates the construction of robust LiF-rich SEI and efficiently inhibits dendrite growth. LiFePO4/Li cells with IBshPE exhibits excellent cycle performance (capacity retention of 98.6% after 80 cycles) and good rate capability (specific capacity of 130.5 mAh g−1 at 2C rate). More importantly, IBshPE is capable of self-repairing damage in the LiFePO4/Li cells and restoring the performance of the cells, thus effectively enhancing the reliability and safety of the battery.

Synergistic osteogenic and angiogenic effects of KP and QK peptides incorporated with an injectable and self-healing hydrogel for efficient bone regeneration.

Irregular defects generated by trauma or surgery in orthopaedics practice were usually difficult to be fitted by the preformed traditional bone graft substitute. Therefore, the injectable hydrogels have attracted an increasing interest for bone repair because of their fittability and mini-invasivity. However, the uncontrollable spreading or mechanical failures during its manipulation remain a problem to be solved. Moreover, in order to achieve vascularized bone regeneration, alternatives of osteogenic and angiogenic growth factors should be adopted to avoid the problem of immunogenicity and high cost.In this study, a novel injectable self-healing hydrogel system (GMO hydrogel) loaded with KP and QK peptides had been developed for enhancing vascularized regeneration of small irregular bone defect. The dynamic imine bonds between gelatin methacryloyl and oxidized dextran provided the GMO hydrogel with self-healing and shear-thinning abilities, which led to an excellent injectability and fittability. By photopolymerization of the enclosed GelMA, GMO hydrogel was further strengthened and thus more suitable for bone regeneration. Besides, the osteogenic peptide KP and angiogenic peptide QK were tethered to GMO hydrogel by Schiff base reaction, leading to desired releasing profiles. In vitro, this composite hydrogel could significantly improve the osteogenic differentiation of BMSCs and angiogenesis ability of HUVECs. In vivo, KP and QK in the GMO hydrogel demonstrated a significant synergistic effect in promoting new bone formation in rat calvaria. Overall, the KP and QK loaded GMO hydrogel was injectable and self-healing, which can be served as an efficient approach for vascularized bone regeneration via a minimally invasive approach.

Self-powered multi-color display based on stretchable self-healing alternating current electroluminescent devices

Multi-color displays enabled with self-powering capability possess unique superiority in information communications for the internet of things (IoT). Here, we present a novel self-powered self-healing multi-color display by integrating the intrinsically stretchable multi-color alternating current electroluminescent (ACEL) devices with the triboelectric nanogenerators (TENGs). By introducing the reversible dynamic imine bonds, PDMS is empowered with superb stretchability (2500%) and high self-healing efficiency (96%) under room temperature. With such stretchable and self-healing PDMS (SSH-PDMS) as the substrate of electrodes and the matrix of emission layers, intrinsically stretchable and self-healing ACEL (SSH-ACEL) devices are fabricated. The self-powered multi-color ACEL display is demonstrated by assembling the modules of SHH-ACEL devices with typical contact-separation mode TENGs. This work may provide a widely adaptable platform for self-powered communication in IoT.

Tying Covalent Organic Frameworks through Alkene Metathesis and Supported Platinum as Efficient Catalysts for Hydrosilylation.

Recently there has been a great interest in covalent organic frameworks due to their fascinating properties. Current approaches to improve their hydrolytic stability mainly rely on the transformation of the dynamic bonds into strong and irreversible bonds, but these approaches also reduce the versatility of the frameworks. Herein, we would like to demonstrate a solution to this dilemma by forming hierarchical bonds through olefin metathesis to produce highly stable COFs. Our approach allows unprecedented opportunities for post-modification of the inner space through the dynamic imine bonds while maintaining the integrity of the framework. Specifically, we demonstrate an amorphous-to-crystalline transformation. In addition, the porosity can be enhanced by up to 70% after full removal of the amine subunits. Overall, our work provides a new direction for the generation of highly stable while still versatile COFs. Meanwhile, platinum(II) complexes can be supported on BHU-2 (Pt@BHU-2) or BHU-2-Oxidate(Pt@BHU-2-Oxidate) as efficient catalysts for hydrosilylation.

Hydrazone bond enhance the mechanical properties, heating resistance, and water resistance of imine-based thermosets

The development of dynamic imine bonds offers a solution to the recycling and repair issues related to conventional petroleum-based thermosetting resins and provides a closed-loop method for utilization towards a circular thermosetting materials economy. Despite recent advances, however, the poor mechanical properties, low heat resistance, and bad water-resistance of imine-based thermosets limit their application. In this study, the biomass dynamic hydrazone bonds were introduced into imine thermosets networks that can enhance the mechanical properties and heating resistance by hydrogen bonding. The prepared biomass hydrazone-imine thermosets exhibit excellent heat resistance (Tg = 215 °C) and tensile strength (56.1 MPa). The properties of the hydrazone-imine thermosets can be readily adjusted by controlling the number of hydrazone bonds. Molecular dynamics calculation of hydrazone-imine thermosets model provides mechanistic insights to how the number of hydrazone bonds manipulating the performance of the themosets. Moreover, the introduction of hydrazone bonds does not affect to the recyclability and repairability of the hydrazone-imine thermosets. Additionally, incorporating hydrazone bonds can enhance the water resistance of imine-based thermosets. Comprehensively, this work provide a sustainable way to design and prepared high-value intelligence thermosets.

Rheology and texture analysis of gelatin/dialdehyde starch hydrogel carriers for curcumin controlled release

A hydrogel carrier was prepared by synergistic cross-linking of dynamic imine bonds and hydrogen bonds between gelatin and dialdehyde starch (DS). The dynamic gelation process and rheological and mechanical properties of hydrogels with different concentrations of DS were studied by dynamic rheology and texture analysis. By changing the content of DS, the gelation kinetics of the hydrogel were adjusted to determine the different gelation times and ensure good injectability. Hydrogels have a stable and firm network structure, and the network can regenerate rapidly after dissociation and collapse. The hydrogel had self-recovery and fatigue resistance, and its hardness, elasticity, deformation capacity, compressive strength and modulus increased with increasing DS content. The hydrogel had good pH-dependent controlled-release ability for curcumin. Injectable hydrogels with biocompatibility, tunable mechanical properties and self-healing properties were used as drug or nutrient delivery carriers for more controlled placement and release.

Highly stretchable and stretch-induced fluorescence chromism self-healing materials based on boroxine and dynamic imine bond

A new self-healing luminescent polymer obtained by combining double covalent bond of boroxine with imine bond was designed. It demonstrated excellent self-healing, high stretchability and stretch-induced fluorescence chromism from green to cyan.

Ultrafast Photochromic Self‐Healing Polymer Gels with Tunable Fluorescence

AbstractPhotoresponsive self‐healing polymer gels have great potential in the fields of optical information storage, artificial intelligence, and wearable flexible devices. Herein, a series of photoresponsive self‐healing gels based on dynamic imine bonds are synthesized in which the photoresponsive functions are achieved by the incorporation of the chromophore 1,2‐bis(5′‐formyl‐2′‐methylthien‐3′‐yl)perfluorocyclopentene (DEA) and the fluorophore 2,5‐dimethoxybenzene‐1,4‐diformaldehyde derivatives (DBD) through the Schiff base reactions between DEA/DBD and aminopropylmethylsiloxane‐dimethylsiloxane copolymers. The gels show ultrafast photoresponsive ability with the transition from yellow to blue within 10 s under 254 nm UV–Vis and subsequent color restoration within 20 s under visible light, derived from the fast ring‐closure and ‐opening transition of DEA. Interestingly, the molecular states of DEA have influence on the on–off intensity of the fluorescence. The gels with ring‐opened DEA show stronger blue fluorescence than the ones with ring‐closed DEA. In addition, the cross‐linked dynamic imine bond enables the gels to self‐heal quickly, and the wound disappears within 10 min without any external stimuli.

Fabrication of Multiresponsive Magnetic Nanocomposite Double-Network Hydrogels for Controlled Release Applications.

Nanocomposite double-network hydrogels (ncDN hydrogels) have been demonstrated as promising biomaterials to present several desired properties (e.g., high mechanical strength, stimuli-responsiveness, and local therapy) for biomedicine. Here, a new type of ncDN hydrogels featuring definable microstructures and properties as well as multistimuli responsiveness for controlled release applications is developed. Amine-functionalized iron oxide nanoparticles (IOPs_NH2 ) are used as nanoparticle cross-linkers to simultaneously connect the dual networks of gelatin (Gel) and polydextran aldehyde (PDA) through hydrogen bonding, electrostatic interactions, and dynamic imine bonds. The pH- and temperature-responsive Gel/PDA/IOP_NH2 ncDN hydrogels present a fast release profile of proteins at acidic pH and high temperature. Besides, IOP_NH2 also contributes the magnetic-responsiveness to the ncDN hydrogels, allowing the use of magnetic field to generate heat to facilitate the structural change of hydrogels and the subsequent applications. Taken together, a versatile ncDN hydrogel platform capable of multistimuli responsiveness and local heating for controlled release is developed for advanced biomedical applications.

Super Tough and Spontaneous Water‐Assisted Autonomous Self‐Healing Elastomer for Underwater Wearable Electronics (Adv. Sci. 21/2021)

Underwater Wearable Electronics In article number 2102275, Cyuan-Lun He, Fang-Cheng Liang, Chi-Ching Kuo and co-workers present a novel underwater self-healing polymer, based on synergistically dynamic covalent Schiff-based imine bonds with hydrogen bonds, which is eco-friendly, economical, waterproof, and resilient. It has outstanding performance in terms of stretchability (9050%), self-healing efficiency (95%), self-healing time (1 h at room temperature), and toughness (144.2 MJ m−3), giving it high potential for integration into underwater electronics.

Sustainable and malleable polyurethane networks from castor oil and vanillin with tunable mechanical properties

Castor oil (CSO)-derived polyurethanes (PUs) are limited by the low mechanical performance and non-reprocessability arisen from their permanently crosslinked structures with high crosslink density and flexible network backbone. In this study, we report malleable polyurethane networks prepared from CSO and hexamethylene diisocyanate with vanillin derived Schiff base (VSB) as a multifunctional monomer. On one hand, VSB with multiple rigid benzene rings and two hydroxyl groups works as a structure modifier to regulate network stiffness and crosslink density of the PUs, which allows us to tailor their mechanical properties over a broad range from soft to tough and hard depending on the content of VSB. On the other hand, VSB with dynamic imine bonds provides the PUs with vitrimeric properties including malleability, thermal processability, and recyclability via network topological rearrangement as a result of imine exchange reaction at elevated temperatures. Consequently, we achieved malleable, processable, and recyclable CSO-derived PU vitrimers with tunable mechanical properties (from elastomer to tough and hard plastics), which would improve the viability and sustainability of CSO-based PUs.

Bioinspired Integration of Naturally Occurring Molecules towards Universal and Smart Antibacterial Coatings

AbstractSurface‐independent smart antibacterial coatings with on‐demand antibiotics release profiles have attracted increasing attention in medical instruments, antibiotics delivery platforms, and implanted devices. Although several approaches have been well documented, the facile preparation of antibacterial coatings onto universal substrates with high antibiotics loading efficiencies, tunable drug release profiles, and excellent antibacterial performances is still met with many challenges, especially related to the redundant coating material synthesis and selective substrate fabrication process. To resolve this issue, the authors report a facile and robust fabrication method towards smart antibacterial coating surfaces on various substrates via a one‐pot integration of two types of naturally occurring building blocks, aminoglycosides and protocatechualdehyde in the presence of plant enzyme horseradish peroxidase. The simultaneous dynamic imine bonds formation and enzymatic polymerization within the system during the one‐pot reaction enable the facile fabrication of diverse surface‐independent smart antibacterial coatings, which can demonstrate several promising features including high drug loading and dynamic (i.e., pH‐responsive) properties, tunable and on‐demand antibiotics release behaviors, and efficient antibacterial activities both in vitro and in vivo. This work may offer new opportunities towards the robust and universal antibacterial coating materials by the bioinspired integration of all natural building blocks.

Bio-based vitrimer-like polyurethane based on dynamic imine bond with high-strength, reprocessability, rapid-degradability and antibacterial ability

Synthesis of vitrimer with dynamic covalent bond is a surprising solution to overcome the inherent limitations of traditional thermosets. A bio-based vitrimer-like polyurethane formed by castor oil, vanillin, m-xylylenediamine and 4,4′-dicyclohexylmethane diisocyanate in the preparation has superior mechanical properties, good solvent resistance, good thermal stability. Furthermore, the existence of dynamic imine bond in the vitrimer-like polyurethane is prone for polyurethane to rapid stress relaxation behavior, remoldability, weldability, antibacterial ability. With the hydrolysis of the imine bond, the material can be rapidly degraded at 60 °C for 1 h. In addition, it's commendable that the material exhibits excellent reprocessability that can be maintained at 86% even after 3 consecutive smash/mold pressing cycles. This work provides a promising method to manufacture bio-based polyurethane thermosets with excellent reprocessability, rapidly-degradable and antibacterial property, which has also promoted the high-value utilization of biomass materials.