Supramolecular Soft Material Enabled by Metal Coordination and Hydrogen Bonding: Stretchability, Self-Healing, Impact Resistance, 3D Printing, and Motion Monitoring

Self-Healing Flexible Sensor Based on Epoxidized Natural Rubber with the Synergistic Effect of Coordination and Hydrogen Bonds

The use of highly tensile and self-healing conductive composites has gained considerable interest due to their wide range of applications in healthcare, sensors, and robotics. Epoxidized natural rubber (ENR), known for its ability to undergo highly reversible deformation, can be utilized in strain sensors to effectively transmit a broader range of signal changes. In this study, we introduced a self-healing ENR composite specifically designed for high-strain sensors. The rubber molecular chains were enhanced with hydrogen bonds and metal coordination bonds, allowing the matrix material to autonomously repair itself through these interactions. Following a repair period of 12 h at 45 °C, the composites achieve a repair efficiency exceeding 90%. Furthermore, by incorporating conductive fillers into the matrix using multistage layering, the resulting composite has good electrical conductivity, thermal conductivity, and hydrophobicity. In addition, this composite presents good sensitivity even at large strain (strain in the range of 50-200%, GF = 7.65). In conclusion, this self-healing nanocomposite, characterized by its high strain sensitivity, holds immense potential for various strain sensor applications.

An injectable biomimetic hydrogel adapting brain tissue mechanical strength for postoperative treatment of glioblastoma without anti-tumor drugs participation

Adapting the mechanical strength between the implant materials and the brain tissue is crucial for the postoperative treatment of glioblastoma. However, no related study has been reported. Herein, we report an injectable lipoic acid‑iron (LA-Fe) hydrogel (LFH) that can adapt to the mechanical strength of various brain tissues, including human brain tissue, by coordinating Fe3+ into a hybrid hydrogel of LA and its sodium salt (LANa). When LFH, which matches the mechanical properties of mouse brain tissue (337 ± 8.06 Pa), was injected into the brain resection cavity, the water content of the brain tissue was maintained at a normal level (77%). Similarly, LFH did not induce the activation or hypertrophy of glial astrocytes, effectively preventing brain edema and scar hyperplasia. Notably, LFH spontaneously degrades in the interstitial fluid, releasing LA and Fe3+ into tumor cells. The redox couples LA/DHLA (dihydrolipoic acid, reduction form of LA in cells) and Fe3+/Fe2+ would regenerate each other to continuously provide ROS to induce ferroptosis and activate immunogenic cell death. As loaded the anti-PDL1, anti-PDL1@LFH further enhanced the efficacy of tumor-immunotherapy and promoted tumor ferroptosis. The injectable hydrogel that adapted the mechanical strength of tissues shed a new light for the tumor postoperative treatment.

Hierarchical Supramolecular Aggregation of Molecular Nanoparticles for Granular Materials with Ultra High-Speed Impact-Resistance

The high-speed impact-resistanct materials are of great significance while their development is hindered by the intrinsic tradeoff between mechanical strength and energy dissipation capability. Herein, the new chemical system of molecular granular material (MGM) is developed for the design of impact-resistant materials from the supramolecular complexation of sub-nm molecular clusters (MCs) and hyper-branched polyelectrolytes. Their hierarchical aggregation provides the origin of the decoupling of mechanical strengths and structural relaxation dynamics. The MCs' intrinsic fast dynamics afford excellent high-speed impact-resistance, up to 5600 s-1 impact in a typical split-Hopkinson pressure bar test while only tiny boundary cracks can be observed even under 7200 s-1 impact. The high loadings of MCs and their hierarchical aggregates provide high-density sacrificial bonding for the effective dissipation of the impact energy, enabling the protection of fragile devices from the direct impact of over 200 m s-1 bullet. Moreover, the MGMs can be conveniently processed into protective coatings or films with promising recyclability due to the supramolecular interaction feature. The research not only reveals the unique relaxation dynamics and mechanical properties of MGMs in comparison with polymers and colloids, but also develops new chemical systems for the fabrication of high-speed impact-resistant materials.

An organic/inorganic hybrid soft material for supramolecular adhesion

Thioctic acid (TA) has been widely used to construct soft materials via supramolecular copolymerization with organic chemicals. In this study, TA and the inorganic compound MoS2 are used to fabricate poly[TA-MoS2] via dynamic covalent and supramolecular interactions. Poly[TA-MoS2] exhibits good and long-lasting adhesion performance on various artificial surfaces, with an adhesion strength up to 3.72 MPa (15 days). Further, it exhibits tough adhesion effects in an aqueous environment. Moreover, poly[TA-MoS2] displays good thermal processing behavior, thus enabling its molding through 3D printing.

Wearable and Recyclable Water-Toleration Sensor Derived from Lipoic Acid

Flexible wearable sensors recently have made significant progress in human motion detection and health monitoring. However, most sensors still face challenges in terms of single detection targets, single application environments, and non-recyclability. Lipoic acid (LA) shows a great application prospect in soft materials due to its unique properties. Herein, ionic conducting elastomers (ICEs) based on polymerizable deep eutectic solvents consisting of LA and choline chloride are prepared. In addition to the good mechanical strength, high transparency, ionic conductivity, and self-healing efficiency, the ICEs exhibit swelling-strengthening behavior and enhanced adhesion strength in underwater environments due to the moisture-induced association of poly(LA) hydrophobic chains, thus making it possible for underwater sensing applications, such as underwater communication. As a strain sensor, it exhibits highly sensitive strain response with repeatability and durability, enabling the monitoring of both large and fine human motions, including joint movements, facial expressions, and pulse waves. Furthermore, due to the enhancement of ion mobility at higher temperatures, it also possesses excellent temperature-sensing performance. Notably, the ICEs can be fully recycled and reused as a new strain/temperature sensor through heating. This study provides a novel strategy for enhancing the mechanical strength of poly(LA) and the fabrication of multifunctional sensors.

Supramolecular/Dynamic Covalent Design of High-Performance Pressure-Sensitive Adhesive from Natural Low-Molecular-Weight Compounds

Adhesive materials have played an essential role in the history of humanity. Natural adhesives composed of low-molecular-weight monomers have been overshadowed by modern petroleum-based glues. With the development of green economy, the demand for eco-friendly materials has increased. Herein, two natural biocompatible compounds, namely thioctic acid (TA) and malic acid (MA), are selected to prepare a high-performance pressure-sensitive adhesive poly[TA-MA]. This adhesive can be quantitatively obtained via a simple mixing and heating process. Poly[TA-MA] shows interesting and useful properties, including reversible flexibility, high elongation, and good self-healing, owing to its dynamic polymerization pattern and reversible cross-linking behavior. Poly[TA-MA] exhibits excellent adhesion performance under various extreme conditions, such as at low temperatures and in hot water. High values of shear strength (3.86 MPa), peel strength (7.90 N cm-1), loop tack (10.60 N cm-1), tensile strength (1.02 MPa), and shear resistance (1628 h) demonstrate the strong adhesive effect of poly[TA-MA]. Additionally, TA can be regenerated in the monomer forms from poly[TA-MA] with high recovery rate (>90%). Meanwhile, strong anti-bacterial behavior of poly[TA-MA] is recorded. This study not only reported a new pressure-sensitive adhesive but also fully displayed the feasibility of using natural small molecules to achieve robust surface adhesion.

Enhanced Intrinsic Self-Healing Performance of Mussel Inspired Coating via In-Situ Cation Capture

Under damp or aquatic conditions, the corrosion products deposited on micro-cracks/pore sites bring about the failure of intrinsically healable organic coatings. Inspired by mussels, a composite coating of poly (methyl methacrylate-co-butyl acylate-co-dopamine acrylamide)/phenylalanine-functionalized boron nitride (PMBD/BN-Phe) is successfully prepared on the reinforcing steel, which exhibits excellent anti-corrosion and underwater self-healing capabilities. The self-healing property of PMBD is derived from the synergistic effect of hydrogen bonding and metal-ligand coordination bonding, and thereby the continuous generation of corrosion products can be significantly suppressed through in situ capture of cations by the catechol group. Furthermore, the corrosion protection ability can be remarkably improved by the labyrinth effect of BN and the inhibition role of Phe, and the desired interfacial compatibility can be formed by the hydrogen bonds between BN-Phe and PMBD matrix. The corrosion current density (icorr) of PMBD/BN-Phe coating is determined as 7.95 × 10-11 A cm-2. The low-frequency impedance modulus (|Z|f  =  0.0 1 Hz is remained at 3.47 × 109 Ω cm2, indicating an ultra-high self-healing efficiency (≈89.5%). It is anticipated to provide a unique strategy for development of an underwater self-healing coating and robust durability for application in anti-corrosion engineering of marine buildings.

A supramolecular approach for converting renewable biomass into functional materials

The rational transformation and utilization of biomass have attracted increasing attention because of its high importance in sustainable development and green economy. In this study, we used a supramolecular approach to convert biomass into functional materials. Six biomass raw materials with distinct chemical structures and physical properties were copolymerized with thioctic acid (TA) to afford poly[TA-biomass]s. The solvent-free copolymerization leads to the convenient and quantitative fabrication of biomass-based versatile materials. The non-covalent bonding and reversible solid-liquid transitions in poly[TA-biomass]s endow them with diversified features, including thermal processability, 3D printing, wet and dry adhesion, recyclability, impact resistance, and antimicrobial activity. Benefiting from their good biocompatibility and nontoxicity, these biomass-based materials are promising candidates for biological applications.

Fluorescence color change of supramolecular polymer networks controlled by crown ether-cation recognition

We report a fluorescent supramolecular polymer networks (SPNs) system based on crown ether-cation recognition. The polymer side chains bear ammonium cations, which can be recognized by host molecules with a B15C5 unit and a quinoline group at each end. The quinoline group makes the host molecule exhibit blue fluorescence. After the formation of SPNs, the recognition of the crown ether-cation transforms the blue fluorescence into yellow fluorescence. The accompanying fluorescence color change during the formation of SPNs makes it with potential applications in the fields of display, printing, information storage, and bioimaging.