A Promising Compound for Green Multiresponsive Materials Based on Acyl Carrier Protein

A gel that exhibits intrinsically multiple-responsive behavior was prepared from an oligopeptide and studied. ACP(65-74) is an active decapeptide fragment of acyl carrier protein. We investigated 3% w/v ACP(65-74)-NH2 self-healing physical gels in water, glycerol carbonate (GC), and their mixtures. The morphology was investigated by optical, birefringence, and confocal laser scanning microscopy, circular dichroism, Fourier transform infrared, and fluorescence spectroscopy experiments. We found that all samples possess pH responsiveness with fully reversible sol-to-gel transitions. The rheological properties depend on the temperature and solvent composition. The temperature dependence of the gels in water shows a peculiar behavior that is similar to that of thermoresponsive polymer solutions. The results reveal the presence of several β-sheet structures and amyloid aggregates, offering valuable insights into the fibrillation mechanism of amyloids in different solvent media.

Electroconductive and free-shapeable nanocomposite hydrogels with an ultrafast self-healing property and high stretchability performance

Conductive self-healing hydrogels as a fascinating class of materials have received much attention in recent years and been widely used in many fields. However, a long healing time and poor electrical conductivity have limited their extended applications. To overcome these shortcomings, we fabricated an excellent conductive self-healing hydrogel by embedding a nanocomposite of Ag nanoparticles and reduced graphene oxide (Ag/RGO) in PVA-borax dynamic networks, which exhibits a relatively high conductivity (4.43 S m-1), good flexibility and excellent self-healing properties without any external stimuli. The multifunctional hydrogel could self-heal within 3 s at room temperature. It also exhibits an excellent free-shapeable property like clay such that it can be modeled into any different complex geometrical shape as desired. It is expected to have potential applications in many fields such as flexible electronic wearable devices, sensors, rechargeable batteries, and biomaterials.

Self-healing conductive hydrogels: preparation, properties and applications

Conductive hydrogels have generated great interest in biomedical and electrical fields. However, conventional conductive hydrogels usually lack self-healing properties, which might be unfavorable for their application. Conductive self-healing hydrogels with excellent performance for applications in the biomedical and electrical fields are growing in number. In this review paper, the progress related to conductive self-healing hydrogels is summarized. The self-healing mechanism is classified to demonstrate the design and synthesis of conductive self-healing hydrogels and their applications in tissue engineering, wound healing, electronic skin, sensors and self-repaired circuits are presented and discussed. The future development of conductive self-healing hydrogels and problems that need to be solved are also described.

A bi-component supramolecular gel for selective fluorescence detection and removal of Hg2+ in water

A bi-component supramolecular gel (RQ) was successfully constructed by the assembly of the gelators 4-aminophenyl functionalized naphthalimide derivative (R) and tri-(pyridine-4-yl)-functionalized trimesic amide (Q) in DMSO-H2O (6.1 : 3.9, v/v) binary solution. The gel RQ exhibits excellent self-healing capacity. Interestingly, the RQ could fluorescently detect and reversibly remove Hg2+ from water through cation-π interactions with high selectivity, efficient adsorption and quick response. The limit of lowest detection (LOD) of the RQ for Hg2+ is 4.52 × 10-8 M and the separation ratio is 91.14%. Moreover, the RQ could be efficiently recycled and regenerated with little loss via a simple treatment by I-. Notably, thin films based on RQ and RQ + Hg2+ were prepared, which could serve as convenient and efficient test tools for the detection of Hg2+ and I-, respectively. This work provided an efficient method and novel supramolecular gel material for the separation and detection of Hg2+.

Infinite coordination polymer networks: metallogelation of aminopyridine conjugates and in situ silver nanoparticle formation

Herein we report silver(i) directed infinite coordination polymer network (ICPN) induced self-assembly of low molecular weight organic ligands leading to metallogelation. Structurally simple ligands are derived from 3-aminopyridine and 4-aminopyridine conjugates which are composed of either pyridine or 2,2'-bipyridine cores. The cation specific gelation was found to be independent of the counter anion, leading to highly entangled fibrillar networks facilitating the immobilization of solvent molecules. Rheological studies revealed that the elastic storage modulus (G') of a given gelator molecule is counter anion dependent. The metallogels derived from ligands containing a bipyridine core displayed higher G' values than those with a pyridine core. Furthermore, using single crystal X-ray diffraction studies and ¹H-¹⁵N two-dimensional (2D) correlation NMR spectroscopy, we show that the tetracoordination of silver ions enables simultaneous coordination polymerization and metallosupramolecular cross-linking. The resulting metallogels show spontaneous, in situ nanoparticle (d < 2-3 nm) formation without any additional reducing agents. The silver nanoparticle formation was followed using spectroscopic studies, and the self-assembled fibrillar networks were imaged using transmission electron microscopy (TEM) imaging.

An efficient supramolecular adsorbent for co-adsorption of dyes and metal ions from wastewater and its application in self-healing materials

Herein, a novel type of two-component supramolecular adsorbent, 2-OA, was developed based on non-covalent interactions using tetrazolyl derivative with octadecylamine (OA) and fully characterized using a number of structural and spectral techniques. The self-assembled 2-OA gels displayed remarkable stimuli-responsiveness as well as shape-persistent and self-healing properties. In addition, it was found that the adsorbent 2-OA was able to remove dyes (10 kinds of cationic and anionic dyes) and metal ions (Cu²⁺ and Fe²⁺) simultaneously from wastewater owing to synergistic electrostatic attraction, hydrogen-bonding, and hydrophobic and coordination interactions. It also exhibited excellent co-adsorption capability to dye mixtures and binary mixtures of dyes and metal ions. In particular, the dye/metal-loaded adsorbents could be obtained easily from the aqueous phase, and recycling of the adsorbents could thus be achieved. These results suggest that the supramolecular gel 2-OA not only has great potential application in wastewater treatment but also provides a strategy for the development of intriguing self-healing materials.

Giant Enhancement of Carrier Mobility in Bimetallic Coordination Polymers

Electrically conductive metal-organic coordination polymers (CPs) are promising candidates for a variety of technological applications. However, poor energetic and spatial overlap between the sp-electrons of organic ligands and the d-electrons of metal ion often blocks an effective charge transport (mobility) across CPs. Herein, we present a bimetallic design principle for enhancing carrier mobility in CPs. Bimetallic CPs of Fe(III) and Cr(III) ions coordinated to 1,3,5-benzenetricarboxylic acid (BTC) ligand (Fe-BTC-Cr) exhibited remarkably high carrier mobility at the matching mole ratio (1:1) with enhancement factors of 10² and 10⁴ in comparison to those of monometallic parents, Fe-BTC and Cr-BTC, respectively. The observation was substantiated by lowering of the band gap between the valence band and the conduction band upon the formation of a hybrid p-n-type structure in the bimetallic CPs. The direct current conductivity values of the CPs measured by four-probe technique were in good agreement with the alternating current conductivity values obtained from the electrochemical impedance spectroscopy. Our flexible approach of picking and choosing the appropriate combination of metal ions from the periodic table is expected to generate various CPs with desirable semiconducting properties.

An Electrically and Mechanically Autonomic Self-healing Hybrid Hydrogel with Tough and Thermoplastic Properties

Conductive hydrogels are a class of composite materials that usually comprise hydrated polymers and conductive materials. Practical application requires the conductive hydrogels to have various properties such as high conductivity, toughness, self-healing, facile processing ability, and so on. Although challenging to have all the above-mentioned properties, a composite material composed of polymer hydrogel with embedded Au nanoparticles (i.e., P(NaSS)/P(VBIm-Cl)/PVA@Au) was found to show the comprehensive properties above in this paper. For example, P(NaSS)/P(VBIm-Cl)/PVA@Au exhibits mechanical and electrical self-healing properties at ambient conditions. In addition, P(NaSS)/P(VBIm-Cl)/PVA@Au is tough and thermoplastic, potentially making it useful for a variety of applications.

Supramolecular metallogels with bulk self-healing properties prepared by in situ metal complexation

In this feature article, we discuss a series of contributions dealing with the in situ fabrication of supramolecular metallogels (i.e. using low molecular weight ligands and metal ions) that show self-healing properties of the bulk gel phase after complete physical segregation. Most of the advances in this area have taken place during the last three years and are mainly represented by organogels, whereas examples of hydrogels and organic-aqueous gels are still a minority. In situ gelation via metal-coordination of low molecular weight compounds is conceptually different from the use of premade (e.g. in solution) coordination polymers and polymeric structures as gelators and ligands, respectively. In the case of in situ gelation, the cooperative effects of all components of the mixture (i.e. ligand, metal ion, counterions and solvent molecules) in an appropriate ratio under well-defined experimental conditions play a crucial role in the gelation phenomenon and self-healing properties of the material.