In this review we intend to provide a relatively comprehensive summary of the work of supramolecular hydrogelators after 2004 and to put emphasis particularly on the applications of supramolecular hydrogels/hydrogelators as molecular biomaterials. After a brief introduction of methods for generating supramolecular hydrogels, we discuss supramolecular hydrogelators on the basis of their categories, such as small organic molecules, coordination complexes, peptides, nucleobases, and saccharides. Following molecular design, we focus on various potential applications of supramolecular hydrogels as molecular biomaterials, classified by their applications in cell cultures, tissue engineering, cell behavior, imaging, and unique applications of hydrogelators. Particularly, we discuss the applications of supramolecular hydrogelators after they form supramolecular assemblies but prior to reaching the critical gelation concentration because this subject is less explored but may hold equally great promise for helping ...

Supramolecular Hydrogelators and Hydrogels: From Soft Matter to Molecular Biomaterials

This review explores supramolecular gels as materials for environmental remediation. These soft materials are formed by self-assembling low-molecular-weight building blocks, which can be programmed with molecular-scale information by simple organic synthesis. The resulting gels often have nanoscale ‘solid-like’ networks which are sample-spanning within a ‘liquid-like’ solvent phase. There is intimate contact between the solvent and the gel nanostructure, which has a very high effective surface area as a result of its dimensions. As such, these materials have the ability to bring a solid-like phase into contact with liquids in an environmental setting. Such materials can therefore remediate unwanted pollutants from the environment including: immobilisation of oil spills, removal of dyes, extraction of heavy metals or toxic anions, and the detection or removal of chemical weapons. Controlling the interactions between the gel nanofibres and pollutants can lead to selective uptake and extraction. Furthermore, if suitably designed, such materials can be recyclable and environmentally benign, while the responsive and tunable nature of the self-assembled network offers significant advantages over other materials solutions to problems caused by pollution in an environmental setting.

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Applying low-molecular weight supramolecular gelators in an environmental setting – self-assembled gels as smart materials for pollutant removal

Self-assembled peptide nanostructures have been increasingly exploited as functional materials for applications in biomedicine and energy. The emergent properties of these nanomaterials determine the applications for which they can be exploited. It has recently been appreciated that nanomaterials composed of multicomponent coassembled peptides often display unique emergent properties that have the potential to dramatically expand the functional utility of peptide-based materials. This review presents recent efforts in the development of multicomponent peptide assemblies. The discussion includes multicomponent assemblies derived from short low molecular weight peptides, peptide amphiphiles, coiled coil peptides, collagen, and β-sheet peptides. The design, structure, emergent properties, and applications for these multicomponent assemblies are presented in order to illustrate the potential of these formulations as sophisticated next-generation bio-inspired materials.

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Multicomponent peptide assemblies

Self-healing gels, which are able to restore their original shape/condition after damage, have recently attracted considerable interest. The present review provides an update on the current status of self-healing gels for use in soft self-healing devices, with the main focus on wearable devices. Following a brief introduction of conventional self-healing gels, this review summarizes the current strategies for synthesizing self-healing gels, comparing the properties of polymeric and small molecular self-healing gels. Some of the strengths and weaknesses of these two types of self-healing gels are clearly highlighted. Several typical instances to outline the emerging applications of self-healing gels with partially or fully self-healing devices/materials, including wearable sensors, supercapacitors, lithium batteries, and coatings, are provided. Finally, the current challenges and future perspectives regarding the further development of self-healing gels are also discussed.

Self-Healable Gels for Use in Wearable Devices

A novel chitosan functional gel included with multiwall carbon nanotube and substituted polyaniline as adsorbent for efficient removal of chromium ion

Retention, a crucial process in pesticide application, is heavily affected by the extremely low surface energy and micro/nanostructure of plant leaves. The inadequate retention like bouncing, splas...

Topology-Regulated Pesticide Retention on Plant Leavesthrough Concave Janus Carriers

A glycyrrhetate-containing amphiphile, MGP (1-[2-(methyl glycyrrhetate)-2-oxoethyl]pyridinium bromide), has been synthesized, and found to assemble into supramolecular helical nanofibers in chloroform/aromatic solvents, which are primarily driven by π-π stacking, van der Waals forces, and hydrophobic interactions. During the assembly process, MGP stacked into J-aggregates resulting in the sequestration of the hydrophilic pyridinium cation within the interior with the concomitant projection of its hydrophobic skeleton on the outside surface. Ultimately, this protrusion generated a staggered angle due to the steric hindrance between stacked molecules. This staggered angle further led to molecular misalignments and the formation of helical fibrils, which could twist with each other to fabricate larger helical fibers. Consequently, a gel was formed by intertwining these nanofibers into three-dimensional networks. Using this strategy, we found that other triterpenoid-tailored pyridinium amphiphiles are also potential scaffolds for supramolecular helical structures. This work provides a facile approach for the fabrication of supramolecular macroscopic chiral nanostructures that originate from natural products.

Supramolecular helical nanofibers assembled from a pyridinium-functionalized methyl glycyrrhetate amphiphile

Although a few architectures have been fabricated by the self-assembly of natural triterpenoids, the precise control of shape and size is rarely studied. Herein, a methyl oleanolate-bearing amphiphile, 1-[2-(methyl oleanolate)-2-oxoethyl]pyridinium bromide (MOP), has been designed and its assembly behavior was investigated. It was found that the morphologies of MOP assemblies ranged from nanoparticles to rigid microrods and flexible nanofibers in chloroform/p-xylene and methanol/water, respectively. During the assembly process, the systematical variational solvophobic/solvophilic effect resulted in the formation of spherical nanoparticles with opposite dipoles and converse bilayer structures. Moreover, such opposite molecular orientations lead to the inversion of supramolecular chirality and distinct mechanical properties. The driving forces and packing patterns of MOP in each solvent system were clearly demonstrated by the combination of NMR, UV–vis, Fourier transform infrared spectroscopy (FTIR), X-ray ...

Solvent-Directed Assembly of a Pyridinium-Tailored Methyl Oleanolate Amphiphile: Stepwise Growth of Microrods and Nanofibers.

Injectable low-molecular-weight hydrogels (LMWHs) from biocompatible materials have attracted much attention in biomedical applications because they can adapt any desired sizes and cavity shapes. S...

A Simple Injectable Moldable Hydrogel Assembled from Natural Glycyrrhizic Acid with Inherent Antibacterial Activity

Pentacyclic triterpenoids, a class of naturally bioactive products having multiple functional groups, unique chiral centers, rigid skeletons, and good biocompatibility, are ideal building blocks for fabricating versatile supramolecular structures. In this research, the natural pentacyclic triterpenoid glycyrrhetinic acid (GA) was used as a guest molecule for β-cyclodextrin (β-CD) to form a GA/β-CD (1:1) inclusion complex. By means of GA and β-CD pendant groups in N,N'-dimethylacrylamide copolymers, a supramolecular polymer hydrogel can be physically cross-linked by host-guest interactions between GA and β-CD moieties. Moreover, self-healing of this hydrogel was observed and confirmed by step-strain rheological measurements, whereby the maximum storage modulus occurred at a [GA]/[β-CD] molar ratio of 1:1. Additionally, these polymers displayed outstanding biocompatibility. The introduction of a natural pentacyclic triterpenoid into a hydrogel system not only provides a biocompatible guest-host complementary GA/β-CD pair, but also makes this hydrogel an attractive candidate for tissue engineering.

Yuxia Gao

Papers

Topology-Regulated Pesticide Retention on Plant Leavesthrough Concave Janus Carriers

Supramolecular helical nanofibers assembled from a pyridinium-functionalized methyl glycyrrhetate amphiphile

Solvent-Directed Assembly of a Pyridinium-Tailored Methyl Oleanolate Amphiphile: Stepwise Growth of Microrods and Nanofibers.

A Simple Injectable Moldable Hydrogel Assembled from Natural Glycyrrhizic Acid with Inherent Antibacterial Activity

Triterpenoid-Based Self-Healing Supramolecular Polymer Hydrogels Formed by Host–Guest Interactions