Beyond Sol-Gel: Molecular Gels with Different Transitions

The existence of sol–gel transitions is one of the most manifest properties of molecular gels. These transitions reflect their nature since they correspond to the association or dissociation of low weight molecules through non-covalent interactions to form the network constitutive of the gel. Most described molecular gels undergo only one gel-to-sol transition upon heating, and the reverse sol-to-gel transition upon cooling. It has been long observed that different conditions of formation could lead to gels with different morphologies, and that gels can undergo a transition from gel to crystals. However, more recent publications report molecular gels which exhibit additional transitions, for instance gel-to-gel transitions. This review surveys the molecular gels for which, in addition to sol–gel transitions, transitions of different nature have been reported: gel-to-gel transitions, gel-to-crystal transition, liquid–liquid phase separations, eutectic transformations, and synereses.

Joining Two Switches in One Nano-Object: Photoacidity and Photoisomerization in Electrostatic Self-Assembly

Multi-switchable supramolecular nano-objects that respond to irradiation of different wavelengths with changes in size and shape have been built from two different water-soluble molecular switches, joined by attachment to the same polyelectrolyte. Accordingly, two wavelength-specific reactions, namely the excited-state proton dissociation of a photoacid and the cis-trans isomerization of an azo dye, are combined in one supramolecular nano-object that is stable in aqueous solution. The concept has potential in the fields of sensors, molecular motors, and transport.

Peptide-Based Low Molecular Weight Photosensitive Supramolecular Gelators

Over the last couple of decades, stimuli-responsive supramolecular gels comprising synthetic short peptides as building blocks have been explored for various biological and material applications. Though a wide range of stimuli has been tested depending on the structure of the peptides, light as a stimulus has attracted extensive attention due to its non-invasive, non-contaminant, and remotely controllable nature, precise spatial and temporal resolution, and wavelength tunability. The integration of molecular photo-switch and low-molecular-weight synthetic peptides may thus provide access to supramolecular self-assembled systems, notably supramolecular gels, which may be used to create dynamic, light-responsive “smart” materials with a variety of structures and functions. This short review summarizes the recent advancement in the area of light-sensitive peptide gelation. At first, a glimpse of commonly used molecular photo-switches is given, followed by a detailed description of their incorporation into peptide sequences to design light-responsive peptide gels and the mechanism of their action. Finally, the challenges and future perspectives for developing next-generation photo-responsive gels and materials are outlined.

Controlling Syneresis of Hydrogels Using Organic Salts

Supramolecular hydrogels can spontaneously undergo syneresis through fibre–fibre interactions and expel significant amounts of water upon aging. In this process, the hydrophobicity of fibres which regulates the 3D‐rearrangement of the self‐assembled structures during syneresis is important. Here, we show that we can control the hydrophobic microenvironment of gels by incorporating organic salts into the co‐assembled gel fibres thereby enabling control of the macroscopic gel volume phase transition.

Controlling hydrogel properties by tuning non-covalent interactions in a charge complementary multicomponent system

Mixing small molecule gelators is a promising route to prepare useful and exciting materials that cannot be accessed from any of the individual components. Here, we describe pH-triggered hydrogelation by mixing of two non-gelling amphiphiles. The intermolecular interactions among the molecules can be tuned either by controlling the degree of ionization of the components or by a preparative pathway, which enables us to control material properties such as gel strength, gel stiffness, thermal stability, and an unusual shrinking/swelling behaviour.

Stimuli responsive dynamic transformations in supramolecular gels

Supramolecular gels are formed by the self-assembly of small molecules under the influence of various non-covalent interactions. As the interactions are individually weak and reversible, it is possible to perturb the gels easily, which in turn enables fine tuning of their properties. Synthetic supramolecular gels are kinetically trapped and usually do not show time variable changes in material properties after formation. However, such materials potentially become switchable when exposed to external stimuli like temperature, pH, light, enzyme, redox, and chemical analytes resulting in reconfiguration of gel matrix into a different type of network. Such transformations allow gel-to-gel transitions while the changes in the molecular aggregation result in alteration of physical and chemical properties of the gel with time. Here, we discuss various methods that have been used to achieve gel-to-gel transitions by modifying a pre-formed gel material through external perturbation. We also describe methods that allow time-dependent autonomous switching of gels into different networks enabling synthesis of next generation functional materials. Dynamic modification of gels allows construction of an array of supramolecular gels with various properties from a single material which eventually extend the limit of applications of the gels. In some cases, gel-to-gel transitions lead to materials that cannot be accessed directly. Finally, we point out the necessity and possibility of further exploration of the field.

Ultra-Low Molecular Weight Photoswitchable Hydrogelators

Two photoswitchable arylazopyrozoles form hydrogels at a concentration of 1.2 % (w/v). With a molecular weight of 258.28 g mol^-1 , these are the lowest known molecular weight hydrogelators that respond reversibly to light. Photoswitching of the E- to the Z-form by exposure to 365 nm light results in a macroscopic gel→sol transition; nearly an order of magnitude reduction in the measured elastic and loss moduli. In the case of the meta-arylazopyrozole, cryogenic transmission electron microscopy suggests that the 29±7 nm wide sheets in the E-gel state narrow to 13±2 nm upon photoswitching to the predominantly Z-solution state. Photoswitching for meta-arylazopyrozole is reversible through cycles of 365 nm and 520 nm excitation with little fatigue. The release of a rhodamine B dye encapsulated in gels formed by the arylazopyrozoles is accelerated more than 20-fold upon photoswitching with 365 nm light, demonstrating these materials are suitable for light-controlled cargo release.

Rapid Self-Healing and Thixotropic Organogelation of Amphiphilic Oleanolic Acid-Spermine Conjugates

Natural and abundant plant triterpenoids are attractive starting materials for the synthesis of conformationally rigid and chiral building blocks for functional soft materials. Here, we report the rational design of three oleanolic acid-triazole-spermine conjugates, containing either one or two spermine units in the target molecules, using the Cu(I)-catalyzed Huisgen 1,3-dipolar cycloaddition reaction. The resulting amphiphile-like molecules 2 and 3, bearing just one spermine unit in the respective molecules, self-assemble into highly entangled fibrous networks leading to gelation at a concentration as low as 0.5% in alcoholic solvents. Using step-strain rheological measurements, we show rapid self-recovery (up to 96% of the initial storage modulus) and sol ⇔ gel transition under several cycles. Interestingly, rheological flow curves reveal the thixotropic behavior of the gels. To the best of our knowledge, this kind of behavior was not shown in the literature before, neither for a triterpenoid nor for its derivatives. Conjugate 4, having a bolaamphiphile-like structure, was found to be a nongelator. Our results indicate that the position and number of spermine units alter the gelation properties, gel strength, and their self-assembly behavior. Preliminary cytotoxicity studies of the target compounds 2-4 in four human cancer cell lines suggest that the position and number of spermine units affect the biological activity. Our results also encourage exploring other triterpenoids and their derivatives as sustainable, renewable, and biologically active building blocks for multifunctional soft organic nanomaterials.

Intelligent writable material based on a supramolecular self-assembly gel

A simple dual acylhydrazone-functionalized gelator (G1) has been designed and synthesized, and it was found to form a supramolecular organogel (G1-gel) in a mixed solvent of DMF-H2O. The gelator solution shows brilliant blue light upon mixing with Mg2+; this blue light can be erased by saliva or CO32-. Owing to this characteristic, a smart erasable writable material was prepared.

Multiswitchable photoacid-hydroxyflavylium-polyelectrolyte nano-assemblies

Light- and pH-responsive nano-assemblies with switchable size and structure are formed by the association of a photoacid, anthocyanidin, and a linear polyelectrolyte in aqueous solution. Specifically, anionic disulfonated naphthol derivatives, neutral hydroxyflavylium, and cationic poly(allylamine) are used as building blocks for the ternary electrostatic self-assembly, forming well-defined supramolecular assemblies with tunable sizes of 50 to 500 nm. Due to the network of possible chemical reactions for the anthocyanidin and the excited-state dissociation of the photoacid upon irradiation, different ways to alter the ternary system through external triggering are accessible. The structure and trigger effects can be controlled through the component ratios of the samples. Dynamic and static light scattering (DLS, SLS) and ζ-potential measurements were applied to study the size and the stability of the particles, and information on the molecular structure was gained by UV-vis spectroscopy. Isothermal titration calorimetry (ITC) provided information on the thermodynamics and interaction forces in the supramolecular assembly formation.

Stimuli-Sensitive Self-Assembled Tubules Based on Lysine-Derived Surfactants for Delivery of Antimicrobial Proteins

Drug delivery vectors based on amphiphiles have important features such as versatile physicochemical properties and stimuli-responsiveness. Amino acid-based surfactants are especially promising amphiphiles due to their enhanced biocompatibility compared to conventional surfactants. They can self-organize into micelles, vesicles and complex hierarchical structures, such as fibers, twisted and coiled ribbons, and tubules. In this work, we investigated the self-assembly and drug loading properties of a family of novel anionic double-tailed lysine-derived surfactants, with variable degree of tail length mismatch, designated as mLys10 and 10Lysn, where m and n are the number of carbon atoms in the tails. These surfactants form tubular aggregates with assorted morphologies in water that undergo gelation due to dense entanglement, as evidenced by light and electron microscopy. Lysozyme (LZM), an enzyme with antimicrobial properties, was selected as model protein for loading. After the characterization of the interfacial properties and phase behavior of the amphiphiles, the LZM-loading ability of the tubules was investigated, under varying experimental conditions, to assess the efficiency of the aggregates as pH- and temperature-sensitive nanocarriers. Further, the toxicological profile of the surfactants per se and surfactant/LZM hydrogels was obtained, using human skin fibroblasts (BJ-5ta cell line). Overall, the results show that the tubule-based hydrogels exhibit very interesting properties for the transport and controlled release of molecules of therapeutic interest.

Photoresponsive Photoacid-Macroion Nano-Assemblies

In this study, light-responsive nano-assemblies with light-switchable size based on photoacids are presented. Anionic disulfonated napthol derivates and cationic dendrimer macroions are used as building blocks for electrostatic self-assembly. Nanoparticles are already formed under the exclusion of light as a result of electrostatic interactions. Upon photoexcitation, an excited-state dissociation of the photoacidic hydroxyl group takes place, which leads to a more highly charged linker molecule and, subsequently, to a change in size and structure of the nano-assemblies. The effects of the charge ratio and the concentration on the stability have been examined with absorption spectroscopy and ζ-potential measurements. The influence of the chemical structure of three isomeric photoacids on the size and shape of the nanoscale aggregates has been studied by dynamic light scattering and atomic force microscopy, revealing a direct correlation of the strength of the photoacid with the changes of the assemblies upon irradiation.

Transparency and AIE tunable supramolecular polymer hydrogel acts as TEA-HCl vapor controlled smart optical material

Stimuli-responsive optical materials attract lots of attention due to their broad applications. Herein, a novel smart stimuli-responsive supramolecular polymer was successfully constructed using a simple tripodal quaternary ammonium-based gelator (TH). The TH self-assembles into a supramolecular polymer hydrogel (TH-G) and shows aggregation-induced emission (AIE) properties. Interestingly, the transparency and fluorescence of the TH-G xerogel film (TH-GF) could be reversibly regulated by use of triethylamine (TEA) and hydrochloric acid (HCl) vapor. When alternately fumed with TEA and HCl vapor, the optical transmittance of the TH-GF was changed from 8.9% to 92.7%. Meanwhile, the fluorescence of the TH-G shows an "ON/OFF" switch. The reversible switching of the transparency and the fluorescence of the TH-GF is attributed to the assembly and disassembly of the supramolecular polymer TH-G. Based on these stimuli-response properties, the TH-GF could act as an optical material and shows potential applications as smart windows or fluorescent display material controlled by TEA and HCl vapor.

Mesoscale Assembly of Bisteroidal Esters from Terephthalic Acid

A new series of bisteroidal esters was synthesized using a spacer group, sterols and sapogenins as substrates. Steroidal dimers were prepared in high yields employing diesters of terephthalic acid as linkages at the 3β, 3'β steroidal positions. In all attempts to crystallize bisteroids, it was observed that the compounds tended to self-organize in solution, which was detected when employing various solvent systems. The non-covalent interactions (van der Waals) of the steroidal moieties of this series of symmetrical bisteroids, the polarity of the solvents systems, and the different solubilities of the bisteroid aggregates, indeed induce the molecules to self-assemble into supramolecular structures with well-defined organization. Our results show that the self-assembled structures for the bisteroidal derivatives depend on the solvent system used: with hexane/EtOAc, membrane-shaped structures were obtained, while pure EtOAc afforded strand-shaped arrangements. In the CHCl₃/CH₃OH system, thin strands were formed, since van der Waals interactions are lowered in this system, as a consequence of the increased solubility of the bisteroids in CHCl₃. Based on the characterization by SEM and XRD, we show evidence that the phenomenon of self-assembly of bisteroids occurs presenting different morphologies depending on the solvent used. The new steroidal dimer derivatives were characterized by NMR, TGA, DSC, SEM, and XRD. Finally, the molecular structure of one bisteroid was confirmed by single-crystal X-ray analysis.

Light-triggered syneresis of a water insoluble peptide-hydrogel effectively removes small molecule waste contaminants

A short peptide based hydrogel exhibits aqueous insolubility, thixotropy and efficient light induced syneresis. Upon irradiation with UV light, the hydrogel shrinks and expells ∼50% of the solvent. Syneresis is caused by light-triggered trans-cis isomerisation of an azobenzene moiety in the peptide derivative. This expulsion of solvent can be effectively exploited in the removal of low molecular weight contaminants in water.

Highly efficient photocontrolled targeted delivery of siRNA by a cyclodextrin-based supramolecular nanoassembly

A binary supramolecular nanoassembly that can efficiently load siRNA into A549 cancer cells and inhibited cell growth by photo-irradiation was fabricated using α-CD-modified hyaluronic acid and an azobenzene-modified diphenylalanine derivative.

Mechanoresponsive, proteolytically stable and biocompatible supergelators from ultra short enantiomeric peptides with sustained drug release propensity

This report describes the discovery of a set of decanoic acid based amphiphilic derivatives that serves as a template for the stabilization of hydrogel nanoparticles for the sustained release of model drugs.

A self-assembled photoresponsive gel consisting of chiral nanofibers

A novel compound based on a glutamic acid skeleton, containing azobenzene as a photoresponsive group and ureidopyrimidinone (UPy) as a connection site, was designed and synthesized. The monomer is capable of forming an organogel in nonpolar organic solvents and different types of nanostructures in other solvents. The state of the gel and the chirality of the nanostructures could both be adjusted by subsequent light irradiation at different wavelengths. The helical nanofiber-like morphology was verified in the internal structure of the gel. The performance of this gel was investigated by a series of methods, such as UV–vis absorption spectroscopy, circular dichroism, scanning electron microscopy and rheological techniques. This work provides a new method for facile synthesis of chiro-optical gels.

Folic Acid Derived Hydrogel Enhances the Survival and Promotes Therapeutic Efficacy of iPS Cells for Acute Myocardial Infarction

Stem cell therapy has obtained extensive consensus to be an effective method for post myocardial infarction (MI) intervention. Induced pluripotent stem (iPS) cells, which are able to differentiate into multiple cell types, have the potential to generate cardiovascular lineage cells for myocardial repair after ischemic damage, but their poor retention rate significantly hinders the therapeutic efficacy. In the present study, we developed a supramolecular hydrogel which is formed by the self-assembly of folic acid (FA)-modified peptide via a biocompatible method (glutathione reduction) and suitable for cell encapsulation and transplantation. The iPS cells labeled with CM-Dil were transplanted into the MI hearts of mice with or without FA hydrogel encapsulation. The results corroborated that the FA hydrogel significantly improved the retention and survival of iPS cells in MI hearts post injection, leading to augmentation of the therapeutic efficacy of iPS cells including better cardiac function and much less adverse heart remodeling, by subsequent differentiation toward cardiac cells and stimulation of neovascularization. This study reported a novel supramolecular hydrogel based on FA-peptides capable of improving the therapeutic capacity of iPS cells, which held big potential in the treatment of MI.

Bipyridine based metallogels: an unprecedented difference in photochemical and chemical reduction in the in situ nanoparticle formation

Metal co-ordination induced supramolecular gelation of low molecular weight organic ligands is a rapidly expanding area of research due to the potential in creating hierarchically self-assembled multi-stimuli responsive materials. In this context, structurally simple O-methylpyridine derivatives of 4,4'-dihydroxy-2,2'-bipyridine ligands are reported. Upon complexation with Ag(i) ions in aqueous dimethyl sulfoxide (DMSO) solutions the ligands spontaneously form metallosupramolecular gels at concentrations as low as 0.6 w/v%. The metal ions induce the self-assembly of three dimensional (3D) fibrillar networks followed by the spontaneous in situ reduction of the Ag-centers to silver nanoparticles (AgNPs) when exposed to daylight. Significant size and morphological differences of the AgNP's was observed between the standard chemical and photochemical reduction of the metallogels. The gelation ability, the nanoparticle formation and rheological properties were found to be depend on the ligand structure, while the strength of the gels is affected by the water content of the gels.

Gels with sense: supramolecular materials that respond to heat, light and sound

Advances in the field of supramolecular chemistry have made it possible, in many situations, to reliably engineer soft materials to address a specific technological problem. Particularly exciting are "smart" gels that undergo reversible physical changes on exposure to remote, non-invasive environmental stimuli. This review explores the development of gels which are transformed by heat, light and ultrasound, as well as other mechanical inputs, applied voltages and magnetic fields. Focusing on small-molecule gelators, but with reference to organic polymers and metal-organic systems, we examine how the structures of gelator assemblies influence the physical and chemical mechanisms leading to thermo-, photo- and mechano-switchable behaviour. In addition, we evaluate how the unique and versatile properties of smart materials may be exploited in a wide range of applications, including catalysis, crystal growth, ion sensing, drug delivery, data storage and biomaterial replacement.

Supramolecular gelatons: towards the design of molecular gels

The concept of supramolecular gelatons for the design of gels was proposed and described.

Amphiphilic Peptide-Based Supramolecular, Noncytotoxic, Stimuli-Responsive Hydrogels with Antibacterial Activity

A series of peptides with a long fatty acyl chain covalently attached to the C-terminal part and a free amine (-NH₂) group at the N-terminus have been designed so that these molecules can be assembled in aqueous medium by using various noncovalent interactions. Five different peptide amphiphiles with a general chemical formula [H₂N-(CH₂)_nCONH-Phe-CONHC₁₂ (n = 1-5, C₁₂ = dodecylamine)] have been synthesized, characterized, and examined for self-assembly and hydrogelation. All of these molecules [P1 (n = 1), P2 (n = 2), P3 (n = 3), P4 (n = 4), P5 (n = 5)] form thermoresponsive hydrogels in water (pH 6.6) with a nanofibrillar network structure. Interestingly, the hydrogels obtained from compounds P4 and P5 exhibit potential antimicrobial activity against Gram-positive bacteria (Staphylococcus aureus, Bacillus subtilis) and Gram-negative bacteria (Escherichia coli). Dose-dependent cell-viability studies using MTT assay (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) by taking human lung carcinoma (A549) cells vividly demonstrates the noncytotoxic nature of these gelator molecules in vitro. Hemolytic studies show nonsignificant or little hemolysis of human erythrocyte cells at the minimum inhibitory concentration (MIC) of these tested bacteria. Interestingly, it has been found that these antibacterial noncytotoxic hydrogels exhibit proteolytic resistance toward the enzymes proteinase K and chymotrypsin. Moreover, the gel strength and gel recovery time have been successfully modulated by varying the alkyl chain length of the N-terminally located amino acid residues. Similarly, the thermal stability of these hydrogels has been nicely tuned by altering the alkyl chain length of the N-terminally located amino acid residues. In the era of antibiotic-resistant strains of bacteria, the discovery of this new class of peptide-based antibacterial, proteolytically stable, injectable, and noncytotoxic soft materials holds future promise for the development of new antibiotics.

Visible-light/temperature dual-responsive hydrogel constructed by α-cyclodextrin and an azobenzene linked surfactant

A novel photo-responsive anionic surfactant with a dimethylamino-substituted azobenzene located at the end of the hydrophobic chain, 6-(4-dimethylaminoazobenzene-4'-oxy)hexanoate sodium (DAH), has been designed. Through the host-guest interaction in aqueous solution, the trans-DAH could be spontaneously included by using two native α-cyclodextrin (α-CD) molecules. The formed hydrophilic inclusion complex (DAH@2α-CD), however, could act as a gelator to induce the formation of a supramolecular hydrogel, which is driven mainly by hydrogen bonds between neighboring α-CDs and also between the carboxylate in DAH and water. Compared with common hydrogels that consist of networks with fibres or discrete polymer chains, the hydrogel formed by DAH@2α-CD was composed of periodic lamellar structures possessing good shear-thinning behavior and much swollen water layers. The more interesting point for such a hydrogel was its visible-light responsibility for gel-sol reversible phase transition. This originated from the introduction of an electron-donating group (dimethylamino) to azobenzene, which noticeably red-shifted the responsive wavelength for its trans-to-cis isomerization. It was also worth noting that the host-guest interaction between azobenzene in DAH and α-CD significantly improved the photo-transition efficiency from trans to cis forms of azobenzene, which played a critical role in the visible-light responsibility of the hydrogel. This unique visible-light-responsive behavior combined with the inherent thermo-responsive property from α-CD should make the prepared hydrogel find more potential applications in biomedical systems.

Aliphatic-Alcohol-Induced Opaque-to-Transparent Transformation and Application of Solubility Theory in a Bis-Dipeptide-Based Supramolecular Gel

A bis-dipeptide supramolecular gelator (DMPV) is prepared, based on l-valine moieties having a pyridinyl group and a long fatty diamine. It is found that the gelator can immobilize organic/water binary mixed solvents, and gel-to-gel transitions with unprecedented opaque-to-transparent transformations are observed upon using aliphatic alcohols such as methanol, ethanol, 1-propyl alcohol, and isopropanol as the organic components. Morphological investigations indicate that a reassembly process occurs, and microstructure evolutions from agglomerates to nanofibers are observed. Opaque and transparent assemblies can interconvert, and respond and restore under mechanical force and pH stimuli. Moreover, Hansen and Flory-Huggins parameters are used to investigate the effect of the solvent on the gelation performance of DMPV. This may facilitate the structure and solvent optimizations and aid the development of advanced gel systems.

Modulating the Phe–Phe dipeptide aggregation landscape via covalent attachment of an azobenzene photoswitch

A covalently modified trans-H-(l)AzoPhe–Phe–OH dipeptide shows reversible photo-switching between its native fibril and vesicle aggregate morphology.

A tripeptide-based self-shrinking hydrogel for waste-water treatment: removal of toxic organic dyes and lead (Pb2+) ions

A tripeptide-based supramolecular automatically self-shrinking superhydrogel has been discovered for the efficient removal of toxic organic dyes and Pb²⁺ ions from waste-water.

Amphiphilic Metallopolymers for Photoswitchable Supramolecular Hydrogels

A series of amphiphilic metallopolymers is described that features zinc(II) bis-terpyridine coordination nodes as well as a backbone with hydrophobic azoaryl moieties and hydrophilic phenylene-ethynylene units decorated with PEG brushes. Using such metallopolymers at very low concentration, stable, photo-responsive and self-healing hydrogels are obtained. UV irradiation of the gel allows modulation of the degree of hydrophobic π-π interactions between photoisomerizable azoaryl units and a polarity switch that overall induces a fast gel-to-sol transition. Finally, the material phase can be readily and fully restored to the thermodynamically stable state either thermally or photochemically by using visible light. The presented strategy can be further generalized towards modular supramolecular metallopolymers for injectable gels in drug delivery and bio-engineering applications.

On the syneresis of an OPV functionalised dipeptide hydrogel

We describe a new dipeptide hydrogel based on an oligophenylene vinylene core. After gelation, the initial network evolves, expelling solvent and resulting in syneresis. We describe this process and the effects in the bulk properties of the material.

Dendrimers and Dendrons as Versatile Building Blocks for the Fabrication of Functional Hydrogels

Hydrogels have emerged as a versatile class of polymeric materials with a wide range of applications in biomedical sciences. The judicious choice of hydrogel precursors allows one to introduce the necessary attributes to these materials that dictate their performance towards intended applications. Traditionally, hydrogels were fabricated using either polymerization of monomers or through crosslinking of polymers. In recent years, dendrimers and dendrons have been employed as well-defined building blocks in these materials. The multivalent and multifunctional nature of dendritic constructs offers advantages in either formulation or the physical and chemical properties of the obtained hydrogels. This review highlights various approaches utilized for the fabrication of hydrogels using well-defined dendrimers, dendrons and their polymeric conjugates. Examples from recent literature are chosen to illustrate the wide variety of hydrogels that have been designed using dendrimer- and dendron-based building blocks for applications, such as sensing, drug delivery and tissue engineering.

Photo/chemo dual-controlled reversible morphological conversion and chiral modulation of supramolecular nanohelixes with nanosquares and nanofibers

A photo/chemo dually interconvertible system was constructed with switchable morphologies among a nanohelix, nanofiber and nanosquare.

Metastable hydrogels from aromatic dipeptides

The dipeptides FF and FF-NH₂ form metastable hydrogels upon sonication. The hydrogels show instantaneous syneresis upon mechanical contact.

Structure- and solvent-triggered influences in the self-assembly of polyoxometalate–steroid conjugates

The supramolecular structures formed by polyoxometalate–steroid conjugates can be greatly influenced by molecular structures and solution components.

Photoresponsive gelators

We review the different approaches that have been used to form low molecular weight gels that respond to light.