Strong,Self‐Healable,and Recyclable Visible‐Light‐Responsive Hydrogel Actuators

The most pressing challenges for light‐driven hydrogel actuators include reliance on UV light, slow response, poor mechanical properties, and limited functionalities. Now, a supramolecular design strategy is used to address these issues. Key is the use of a benzylimine‐functionalized anthracene group, which red‐shifts the absorption into the visible region and also stabilizes the supramolecular network through π–π interactions. Acid–ether hydrogen bonds are incorporated for energy dissipation under mechanical deformation and maintaining hydrophilicity of the network. This double‐crosslinked supramolecular hydrogel developed via a simple synthesis exhibits a unique combination of high strength, rapid self‐healing, and fast visible‐light‐driven shape morphing both in the wet and dry state. As all of the interactions are dynamic, the design enables the structures to be recycled and reprogrammed into different 3D objects.     

Supramolecular hydrogel microcapsules via cucurbit[8]uril host–guest interactions with triggered and UV-controlled molecular permeability

Host–guest assembly in droplet-based microfluidics opens a new avenue for fabricating supramolecular hydrogel microcapsules with high monodispersity and controlled functionality. In this paper, we demonstrate a single emulsion microdroplet platform to prepare microcapsules with supramolecular hydrogel skins from host molecule cucurbit[8]uril and guest polymer anthracene-functionalized hydroxyethyl cellulose. In contrast to construction of microcapsules from a droplet-in-droplet double emulsion, here the electrostatic attraction between charged polymer and surfactant facilitates formation of defined supramolecular hydrogel skins in a single emulsion. Furthermore, by taking advantage of dynamic interactions and the tunable cross-linked supramolecular hydrogel network, it is possible to prepare microcapsules with triggered and UV-controlled molecular permeability. These could be potentially used in a delivery system for e.g. agrochemicals, nutraceuticals or cosmetics.     

Supramolecular hydrogel formed by glucoheptonamide of l-lysine: simple preparation and excellent hydrogelation ability

We describe the simple preparation of new l-lysine derivatives with a gluconic or glucoheptonic group, their hydrogelation properties, and the thermal and mechanical properties of the supramolecular hydrogels. The l-lysine derivatives with a gluconic group have no hydrogelation ability, while the l-lysine-glucoheptonamide derivatives functioned as hydrogelators. Their hydrogelation abilities increased with the decreasing length of the spacer between the l-lysine segment and the glucoheptonic group. The compound, which has no spacer, formed a supramolecular hydrogel at 0.05 wt % in pure water. The thermal stability and high mechanical strength of the supramolecular hydrogels based on this compound significantly depended on the aqueous solutions. Electron microscopy and FTIR studies demonstrated that the hydrogelators created a three-dimensional network through hydrogen bonding and hydrophobic interactions in the supramolecular hydrogel. In addition, it was found that hydrophobic interactions played an important role in the thermal stability of the supramolecular hydrogel.     

Photoregulated supramolecular hydrogels driven by polyradical interactions

Organic radical as a powerful tool has been extensively applied in synthetic chemistry. However, harnessing radical-mediated noncovalent interactions to fabricate soft materials remains elusive. Here we report a new category of supramolecular hydrogel system held by multiple radical-radical (polyradical) interactions, and its photosensitive cross-linking structure. A simple polyacrylamide with triarylamine (TAA) pendants is designed as the precursor. The TAA units in polymer can be converted into active TAA^•⁺ radical cations with light and further associate each other via TAA^•⁺‒TAA^•⁺ stacking interactions to form stable supramolecular network. Temporal control of the light irradiation dictates the degree of radical stacks, thus regulating the mechanical performance of the resulting hydrogel materials on-demand. Moreover, the reversible collapse of this hydrogels can be promoted by adding radical scavenger or exerting reduction voltage.     

Using a kinase/phosphatase switch to regulate a supramolecular hydrogel and forming the supramolecular hydrogel in vivo

We have designed and synthesized a new hydrogelator Nap-FFGEY (1), which forms a supramolecular hydrogel. A kinase/phosphatase switch is used to control the phosphorylation and dephosphorylation of the hydrogelator and to regulate the formation of supramolecular hydrogels. Adding a kinase to the hydrogel induces a gel-sol phase transition in the presence of adenosine triphosphates (ATP) because the tyrosine residue is converted into tyrosine phosphate by the kinase to give a more hydrophilic molecule of Nap-FFGEY-P(O)(OH)(2) (2); treating the resulting solution with a phosphatase transforms 2 back to 1 and restores the hydrogel. Electron micrographs of the hydrogels indicate that 1 self-assembles into nanofibers. Subcutaneous injection of 2 in mice shows that 80.5 +/- 1.2% of 2 turns into 1 and results in the formation of the supramolecular hydrogel of 1 in vivo. This simple biomimetic approach for regulating the states of supramolecular hydrogels promises a new way to design and construct biomaterials.     

Anions bonded on the supramolecular hydrogel surface as the growth center of biominerals

In this work, a supramolecular hydrogel formed from N,N',N'-tris(3-pyridyl)-trimesic amide was reported to serve as the matrix for the growth of biominerals. The organic hydrogel scaffold contains nitrogen heterocyclic ring and amide groups that can bind anions of the mineral (specially here, carbonate ions and phosphate ions) through hydrogen bonding interactions and act as the biomineralization active sites for growing biominerals. Calcium carbonate nucleated on the site of the hydrogel fiber where carbonate ions bonded and left obvious hydrogel fiber prints on the obtained product. Calcium phosphate grew into curved platelike nanostructures along the hydrogel fibrous network. XRD pattern and FT-IR spectra confirmed the formation of minerals on the hydrogel. The results indicate that the hydrogen bonding interaction can provide strong enough binding force for the growth of the minerals on organic scaffolds. Our finding extends the organic scaffolds into biodegradable small molecule hydrogels and also extends the growth centers of the minerals from conventional carboxylate groups binding Ca(2+) to amide and pyridyl groups binding PO(4)(3-).     

Heat‐Induced Morphological Transformation of Supramolecular Nanostructures by Retro‐Diels–Alder Reaction

Controlling the morphology of supramolecular nanostructures in response to external stimuli is an important challenge in the development of functional soft materials. Here we show that a morphological transformation from 2D nanosheets to a network of 1D nanofibers is triggered by heating, which induces molecular conversion of a bolaamphiphile to a hydrogelator by means of a retro‐Diels–Alder reaction, thereby producing a new heat‐set supramolecular hydrogel. We anticipate that our design will be a starting point for more sophisticated supramolecular systems that integrate the thermodynamics of molecular assembly and the kinetics of chemical reactions to create complex supramolecular nanostructures.     

Self‐Healing Supramolecular Hydrogels for Tissue Engineering Applications

Self‐healing supramolecular hydrogels have emerged as a novel class of biomaterials that combine hydrogels with supramolecular chemistry to develop highly functional biomaterials with advantages including native tissue mimicry, biocompatibility, and injectability. These properties are endowed by the reversibly cross‐linked polymer network of the hydrogel. These hydrogels have great potential for realizing yet to be clinically translated tissue engineering therapies. This review presents methods of self‐healing supramolecular hydrogel formation and their uses in tissue engineering as well as future perspectives.     

Metallogels from Coordination Complexes,Organometallic, and Coordination Polymers

A supramolecular gel results from the immobilization of solvent molecules on a 3D network of gelator molecules stabilized by various supramolecular interactions that include hydrogen bonding, π–π stacking, van der Waals interactions, and halogen bonding. In a metallogel, a metal is a part of the gel network as a coordinated metal ion (in a discrete coordination complex), as a cross‐linking metal node with a multitopic ligand (in coordination polymer), and as metal nanoparticles adhered to the gel network. Although the field is relatively new, research into metallogels has experienced a considerable upsurge owing to its fundamental importance in supramolecular chemistry and various potential applications. This focus review aims to provide an insight into the development of designing metallogelators. Because of the limited scope, discussions are confined to examples pertaining to metallogelators derived from discrete coordination complexes, organometallic gelators, and coordination polymers. This review is expected to enlighten readers on the current development of designing metallogelators of the abovementioned class of molecules.     

Low-molecular-weight photoresponsive supramulecular hydrogel based on a dicationic azobenzene-bridged pyridinium hydrogelator

Photoresponsive supramolecular hydrogel was fabricated from a small azobenzene-bridged dicationic pyridinium salt in the aqueous solution. The UV-vis light triggered reversible gel-sol transformation of such low-molecular-weight supramolecular hydrogel was systematically investigated through various analytical techniques.     

Autonomous Growth of a Spatially Localized Supramolecular Hydrogel with Autocatalytic Ability

Autocatalysis and self‐assembly are key processes in developmental biology and are involved in the emergence of life. In the last decade both of these features were extensively investigated by chemists with the final goal to design synthetic living systems. Herein, we describe the autonomous growth of a self‐assembled soft material, that is, a supramolecular hydrogel, able to sustain its own formation through an autocatalytic mechanism that is not based on any template effect and emerges from a peptide (hydrogelator) self‐assembly. A domino sequence of events starts from an enzymatically triggered peptide generation followed by self‐assembly into catalytic nanofibers that induce and amplify their production over time, resulting in a 3D hydrogel network. A cascade is initiated by traces (10^?18 m ) of a trigger enzyme, which can be localized allowing for a spatial resolution of this autocatalytic buildup of hydrogel growth, an essential condition on the route towards further cell‐mimic designs.     

Viscoelastic and fractal characteristics of a supramolecular hydrogel hybridized with clay nanoparticles

The supramolecular hydrogels derived from low-molecular-mass gelators represent a unique class of soft matters and have important potential applications in biomedical fields, separation technology and cosmetic science. However, they suffer usually from weak mechanical and viscoelastic properties. In this work, we carry out the in situ hybridization of clay nanoparticles (Laponite RD) into the supramolecular hydrogel formed from a low-molecular-mass hydrogelator, 2,6-di[N-(carboxyethyl carbonyl)amino]pyridine (DAP), and investigate the viscoelastic and structural characteristics of resultant hybrid hydrogel. It was found that a small concentration of Laponite RD could lead to a significant increase in the storage modulus, loss modulus or complex viscosity. Compared with neat DAP hydrogel, the hybrid hydrogel has a greater hydrogel strength and a lower relaxation exponent. In particular, the enhancement of the clay nanoparticles to the viscoelastic properties of the DAP hydrogel is more effective in the case of higher DAP concentration. By relating its macroscopic elastic properties to a scaling fractal model, such a hybrid hydrogel was confirmed to be in the strong-link regime and to have a more complex network structure with a higher fractal dimension when compared with neat DAP hydrogel.     

Self‐Healing,Expansion–Contraction,and Shape‐Memory Properties of a Preorganized Supramolecular Hydrogel through Host–Guest Interactions

Supramolecular materials cross‐linked between polymer chains by noncovalent bonds have the potential to provide dynamic functions that are not produced by covalently cross‐linked polymeric materials. We focused on the formation of supramolecular polymeric materials through host–guest interactions: a powerful method for the creation of nonconventional materials. We employed two different kinds of host–guest inclusion complexes of β‐cyclodextrin (βCD) with adamantane (Ad) and ferrocene (Fc) to bind polymers together to form a supramolecular hydrogel (βCD‐Ad‐Fc gel). The βCD‐Ad‐Fc gel showed self‐healing ability when damaged and responded to redox stimuli by expansion or contraction. Moreover, the βCD‐Ad‐Fc gel showed a redox‐responsive shape‐morphing effect. We thus succeeded in deriving three functions from the introduction of two kinds of functional units into a supramolecular material.     

Self‐Healing,Expansion–Contraction,and Shape‐Memory Properties of a Preorganized Supramolecular Hydrogel through Host–Guest Interactions

Supramolecular materials cross‐linked between polymer chains by noncovalent bonds have the potential to provide dynamic functions that are not produced by covalently cross‐linked polymeric materials. We focused on the formation of supramolecular polymeric materials through host–guest interactions: a powerful method for the creation of nonconventional materials. We employed two different kinds of host–guest inclusion complexes of β‐cyclodextrin (βCD) with adamantane (Ad) and ferrocene (Fc) to bind polymers together to form a supramolecular hydrogel (βCD‐Ad‐Fc gel). The βCD‐Ad‐Fc gel showed self‐healing ability when damaged and responded to redox stimuli by expansion or contraction. Moreover, the βCD‐Ad‐Fc gel showed a redox‐responsive shape‐morphing effect. We thus succeeded in deriving three functions from the introduction of two kinds of functional units into a supramolecular material.     

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

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.     

Fluorescent magnesium(II) coordination polymeric hydrogel

A pH and mechano-responsive coordination polymeric gel was developed without the use of long chain hydrophobic groups. The hydrogel was synthesised by reacting the aqueous solution of Mg2+ with the basic aqueous solution of N-(7-hydroxyl-4-methyl-8-coumarinyl)-alanine. The gelation is attributed to the self-aggregation of 1D coordination polymers to form 3D nanostructures through non-covalent interactions to entrap water molecules. The freeze-dried hydrogel exhibits a fibrillar network structure with a uniform ribbon shape. UV/vis absorption studies illustrate that the hydrogel displays a typical pi-pi* transition. The fluorescence intensity of the hydrogel is enhanced drastically with a longer lifetime upon gel formation. Mechanical analysis including dynamic oscillation on shear, steady shear and creep (retardation-relaxation) testing have been performed to elucidate the supramolecular nature of the 3D assembly. Together with the viscoelastic properties and biocompatibility, the Mg2+ hydrogel may find utility as a novel soft material in biomedical applications.     

Hybrid Hydrogels Assembled from Phenylalanine Derivatives and Agarose with Enhanced Mechanical Strength

A roadblock for supramolecular hydrogels is their poor mechanical properties. Herein, to enhance the mechanical strength of supramolecular hydrogels, agarose(AG) was incorporated into the low molecular weight hydrogelator(G1). The results of scanning electron microscopy(SEM), circular dichroism(CD) and Fourier transform infrared spectroscopy(FTIR) prove that G1 gelators can self-assemble into cross-linked network together with AG. The mechanical properties of the gels are characterized by a rotary rheometer and the mechanical properties of the hybrid hydrogels(Hgel) can be significantly improved and may be further tuned by changing the ratio of the two components. For example, the elastic modulus of Hgel Ⅱ[m(G1):m(AG)=7:3] is about 2 times higher than that of G1 hydrogel. The results demonstrate that the mechanical property of hybrid supramolecular hydrogels can be adjusted through the formation of a cross-linked network.     

纳米颗粒增强的手性超分子水凝胶成骨性能

手性超分子水凝胶能够仿生细胞外手性微环境,在组织工程中具有特殊的意义,但其强度和稳定性较低,仍然面临着巨大的挑战.本文将无机羟基磷灰石纳米颗粒(HAP)引人到苯丙氨酸衍生物手性超分子水凝胶(LPF)中以改善其力学性能和生物功能.圆二色光谱和扫描电子显微镜结果显示,HAP掺入后LPF组装手性发生反转.与纯LPF水凝胶相比...     

Long,Multicenter Bonding—A New Concept for Supramolecular Materials

A new concept for constructing supramolecular architectures is discussed. In addition to van der Waals and hydrogen‐bonding intermolecular interactions that primarily account for supramolecular structures for all materials lacking extended 3D network structures, directional, long, multicenter bonding that can occur for anionic, cationic, neutral, and zwitterionic radicals and can direct intermolecular recognition through π interactions and form extended network supramolecular structural motifs.     

Stiff,Multistimuli‐Responsive Supramolecular Hydrogels as Unique Molds for 2D/3D Microarchitectures of Live Cells

Supramolecular hydrogels constructed through molecular self‐assembly of small molecules have unique stimuli‐responsive properties; however, they are mechanically weak in general, relative to conventional polymer gels. Very recently, we developed a zwitterionic amino acid tethered amphiphilic molecule 1 , which gave rise to a remarkably stiff hydrogel comparable with polymer‐based agarose gel, retaining reversible thermal‐responsive properties. In this study, we describe that rational accumulation of multiple and orthogonal noncovalent interactions in the supramolecular nanofibers of 1 played crucial roles not only in the mechanical reinforcement but also in the multistimuli responsiveness. That is, the zwitterionic amino acid moiety and the C C double bond unit of the hydrogelator 1 can function as a pH‐responsive unit and a light‐responsive unit, respectively. We also demonstrated that this stiff and multistimuli‐responsive supramolecular hydrogel 1 is applied as a unique mold for 2D and 3D‐patterning of various substances. More significantly, we succeeded in the fabrication of a collagen gel for spatial patterning, culturing, and differentiation of live cells by using hydrogel 1 molds equipped with 2D/3D microspace channels (100–200 μm in diameter).