Supramolecular hydrogels based on bola-amphiphilic glycolipids showing color change in response to glycosidases

Supramolecular Hydrogels: Design Strategies and Contemporary Biomedical Applications

Self-assembly of supramolecular hydrogels is driven by dynamic, non-covalent interactions between molecules. Considerable research effort has been exerted to fabricate and optimise supramolecular hydrogels that display shear-thinning, self-healing, and reversibility, in order to develop materials for biomedical applications. This review provides a detailed overview of the chemistry behind the dynamic physicochemical interactions that sustain hydrogel formation (hydrogen bonding, hydrophobic interactions, ionic interactions, metal-ligand coordination, and host-guest interactions). Novel design strategies and methodologies to create supramolecular hydrogels are highlighted, which offer promise for a wide range of applications, specifically drug delivery, wound healing, tissue engineering and 3D bioprinting. To conclude, future prospects are briefly discussed, and consideration given to the steps required to ultimately bring these biomaterials into clinical settings.

Development of an Amino Sugar-Based Supramolecular Hydrogelator with Reduction Responsiveness

Stimuli-responsive supramolecular hydrogels are a newly emerging class of aqueous soft materials with a wide variety of bioapplications. Here we report a reduction-responsive supramolecular hydrogel constructed from a markedly simple low-molecular-weight hydrogelator, which is developed on the basis of modular molecular design containing a hydrophilic amino sugar and a reduction-responsive nitrophenyl group. The hydrogel formation ability differs significantly between glucosamine- and galactosamine-based self-assembling molecules, which are epimers at the C4 position, and only the glucosamine-based derivative can act as a hydrogelator.

Enzymatic Hydrolysis-Responsive Supramolecular Hydrogels Composed of Maltose-Coupled Amphiphilic Ureas

Maltose is a ubiquitous disaccharide produced by the hydrolysis of starch. Amphiphilic ureas bearing hydrophilic maltose moiety were synthesized via the following three steps: I) construction of urea derivatives by the condensation of 4-nitrophenyl isocyanate and alkylamines, II) reduction of the nitro group by hydrogenation, and III) an aminoglycosylation reaction of the amino group and the unprotected maltose. These amphiphilic ureas functioned as low molecular weight hydrogelators, and the mixtures of the amphipathic ureas and water formed supramolecular hydrogels. The gelation ability largely depended on the chain length of the alkyl group of the amphiphilic urea; amphipathic urea having a decyl group had the highest gelation ability (minimum gelation concentration=0.4 mM). The physical properties of the supramolecular hydrogels were evaluated by measuring their thermal stability and dynamic viscoelasticity. These supramolecular hydrogels underwent gel-to-sol phase transition upon the addition of α-glucosidase as a result of the α-glucosidase-catalyzed hydrolysis of the maltose moiety of the amphipathic urea.

Biomaterials for Three-Dimensional Cell Culture: From Applications in Oncology to Nanotechnology

Three-dimensional cell culture has revolutionized cellular biology research and opened the door to novel discoveries in terms of cellular behavior and response to microenvironment stimuli. Different types of 3D culture exist today, including hydrogel scaffold-based models, which possess a complex structure mimicking the extracellular matrix. These hydrogels can be made of polymers (natural or synthetic) or low-molecular weight gelators that, via the supramolecular assembly of molecules, allow the production of a reproducible hydrogel with tunable mechanical properties. When cancer cells are grown in this type of hydrogel, they develop into multicellular tumor spheroids (MCTS). Three-dimensional (3D) cancer culture combined with a complex microenvironment that consists of a platform to study tumor development and also to assess the toxicity of physico-chemical entities such as ions, molecules or particles. With the emergence of nanoparticles of different origins and natures, implementing a reproducible in vitro model that consists of a bio-indicator for nano-toxicity assays is inevitable. However, the maneuver process of such a bio-indicator requires the implementation of a repeatable system that undergoes an exhaustive follow-up. Hence, the biggest challenge in this matter is the reproducibility of the MCTS and the associated full-scale characterization of this system's components.

Synthesis and Self-Assembly Properties of Bola-Amphiphilic Glycosylated Lipopeptide-Type Supramolecular Hydrogels Showing Colour Changes Along with Gel-Sol Transition

Supramolecular hydrogels formed by self-assembly of low-molecular-weight amphiphiles (hydrogelators) have attracted significant attention, as smart and soft materials. However, most of the observed stimuli-responsive behaviour of these supramolecular hydrogels are limited to gel-sol transitions. In this study, we present bola-amphiphilic glycosylated lipopeptide-type supramolecular hydrogelators that exhibit reversible thermochromism along with a gel-sol transition. The bola-amphiphiles have mono-, di-, tri- or tetra-phenylalanine (F) as a short peptide moiety. We investigate and discuss the effects of the number of F residues on the gelation ability and the morphology of the self-assembled nanostructures.

Self-Assembly of Nucleoside-Derived Low-Molecular-Weight Gelators: A Thermodynamics and Kinetics Study on Different Length Scales

Biocompatible materials are of paramount importance in numerous fields. Unlike chemically bridge polymer-based hydrogels, low-molecular-weight gelators can form a reversible hydrogel as their structures rely on noncovalent interaction. Although many applications with this type of hydrogel can be envisioned, we still lack their understanding due to the complexity of their self-assembly process and the difficulty in predicting their behaviors (transition temperature, gelation kinetics, the impact of solvent, etc.). In this study, we extend the investigations of a series of nucleoside-derived gelators, which only differ by subtle chemical modifications. Using a multitechnique approach, we determined their thermodynamic and kinetic features on various scale (molecular to macro) in different conditions. Monitored at the supramolecular level by circular dichroism as well as macroscopic scales by rheology and turbidimetry, we found out that the sol-gel and gel-sol transitions are greatly dependent on the concentration and on the mechanisms that are probed. Self-assembly kinetics depends on hydrogel molecules and is modulated by temperature and solvent. This fundamental study provides insight on the impact of some parameters on the gelation process, such as concentration, cooling rate, and the nature of the solvent.

Structural diversification of bola-amphiphilic glycolipid-type supramolecular hydrogelators exhibiting colour changes along with the gel-sol transition

We diversified the structures of bola-amphiphilic glycolipid-type supramolecular hydrogelators that exhibited reversible thermochromism along with a gel-sol transition. The hydrogelators were designed and synthesized to have homo- or hetero-saccharides on each end of their molecules. Herein, the effects of the saccharides' structure on the gelation ability are discussed.

Glycosylation-enhanced biocompatibility of the supramolecular hydrogel of an anti-inflammatory drug for topical suppression of inflammation

Intravitreal/periocular injection of triamcinolone acetonide (TA) suspension is a common uveitis treatment, but it displays a high risk for serious side effects (e.g., high intraocular pressure, retinal toxicity). We report here an intravitreally injectable thermosensitive glycosylated TA (TA-SA-Glu) hydrogel, formed by covalently conjugating glucosamine (Glu) with succinate TA (TA-SA), for treating uveitis. The TA-SA-Glu hydrogelator forms a supramolecular hydrogel spontaneously in aqueous solution with a minimal gelation concentration of 0.25 wt%. Structural analysis revealed that hydrogen bonds assisted by hydrophobic interaction resulted in self-assembled nanofibers. Rheology analysis demonstrated that this TA-SA-Glu hydrogel exhibited a typical thixotropic property. Sustained release of both TA-SA-Glu and TA from the hydrogel occurred throughout the 3-day in vitro release study. The obtained TA-SA-Glu hardly caused cytotoxicity against ARPE-19 and RAW264.7 cells after 24 h of incubation at drug concentration up to 600 μM. In particular, TA-SA-Glu exhibited a comparable anti-inflammatory efficacy to TA in terms of inhibiting the production of nitric oxide, tumor necrosis factor-α, and interleukin-6 in activated RAW264.7 macrophages. Following a single intravitreal injection, 69 nmol TA-SA-Glu hydrogel caused minimal apparent retinal toxicity, whereas the TA suspension displayed significant effects in terms of localized retinal toxicity. A single intravitreal injection of TA-SA-Glu hydrogel was more effective in controlling inflammatory response than that of the TA suspension treatment, particularly in down-regulating the pro-inflammatory Th1 and Th17 effector responses for treating experimental autoimmune uveitis. This study strongly indicates that supramolecular TA-SA-Glu hydrogels may represent a new option for posterior uveitis management.

STATEMENT OF SIGNIFICANCE

Intravitreal/periocular injection of triamcinolone acetonide (TA) suspension is a common uveitis treatment, but suffers a high risk for serious side effects (e.g., high intraocular pressure, retinal toxicity). We generated an injectable glycosylated triamcinolone acetonide hydrogelator (TA-SA-Glu) hydrogel for treating uveitis. Following a single intravitreal injection, the proposed TA-SA-Glu hydrogel hardly caused apparent retinal toxicity at a dosage of 69 nmol per eye. Furthermore, TA-SA-Glu hydrogel was more effective in controlling non-infectious uveitis over than a TA suspension, particularly in terms of down-regulating the pro-inflammatory Th1 and Th17 effector responses for treating experimental autoimmune uveitis (EAU). This study strongly indicates that TA-SA-Glu supramolecular hydrogels may represent a new option for the management of various intraocular inflammations.

The effect of carbohydrate structures on the hydrogelation ability and morphology of self-assembled structures of peptide-carbohydrate conjugates in water

We describe the construction of peptide-carbohydrate conjugates, namely glycopeptides, capable of self-assembling in water. We found that disaccharide structures (epimer or glycosidic-bond geometry) appended to the glycopeptides have a noticeable effect on the hydrogel formation ability as well as the morphology of the self-assembled structures. The soft materials consisting of self-assembled structures with carbohydrates on their surface and various types of morphologies might be useful as matrices to investigate the function of carbohydrates in biological events.

Recent Advances in the Chemistry of Glycoconjugate Amphiphiles

Glyconanoparticles essentially result from the (covalent or noncovalent) association of nanometer-scale objects with carbohydrates. Such glyconanoparticles can take many different forms and this mini review will focus only on soft materials (colloids, liposomes, gels etc.) with a special emphasis on glycolipid-derived nanomaterials and the chemistry involved for their synthesis. Also this contribution presents Low Molecular Weight Gels (LMWGs) stabilized by glycoconjugate amphiphiles. Such soft materials are likely to be of interest for different biomedical applications.

Design Strategies of Stimuli-Responsive Supramolecular Hydrogels Relying on Structural Analyses and Cell-Mimicking Approaches

Stimuli-responsive hydrogels are intriguing biomaterials useful for spatiotemporal controlled release of drugs, cells, and biological cues, cell engineering for various applications, and medical diagnosis. To date, many physical and chemical stimuli-responsive polymer hydrogels have been developed by chemical modification of polymer chains and cross-linking points. In particular, conjugation with biomolecules to polymers produced promising biomolecule-responsive hydrogels. These examples clearly indicate high potentials of stimuli-responsive hydrogels as promising biomaterials. In addition to polymer hydrogels, supramolecular hydrogels formed by the assembly of small molecules (hydrogelators) via noncovalent interactions have also been regarded as unique and promising soft materials due to their flexible programmability in rendering them stimuli-responsive with the larger macroscopic change (i.e., gel-sol transition). This Account describes our strategies for the rational design of stimuli-responsive supramolecular hydrogels and their biological applications. Following the detailed structural analysis of a lead hydrogelator that clearly indicates the appropriate sites for incorporation of stimuli-responsive modules, we designed supramolecular hydrogels capable of responding to simple physical (thermal and light) and chemical (pH and metal ions) stimuli. More importantly, biomolecule-responsive hydrogels were successfully developed by supramolecularly mimicking the complex yet well-ordered structures and functions of live cells containing multiple components (a cell-mimicking approach). Development of biomolecule-responsive supramolecular hydrogels has been difficult as the conventional strategy relies on the chemical incorporation of stimuli-responsive modules, owing to the lack of modules that can effectively respond to structurally diverse and complicated biomolecules. Inspired by natural systems where functional compartments (e.g., cell organelles) sophisticatedly interact with each other, we sought to integrate the two distinct microenvironments of supramolecular hydrogels (the aqueous cavity surrounded by fibers and the fluidic hydrophobic fiber domain) with other functional materials (e.g., enzymes, peptides or proteins, fluorescent chemosensors, or inorganic porous or layered nanomaterials) for biomolecule responses. In situ fluorescence microscopy imaging clearly demonstrated that chemical isolation and crosstalk are highly successful between the integrated microenvironments in supramolecular hydrogels, similar to organelles in living cells, which allow for the construction of unique optical response and sensing systems for biomolecules. Furthermore, programmed hybridization of our chemically reactive hydrogels with appropriate enzymes can provide an unprecedented universal platform for biomolecule-degradable supramolecular hydrogels. Such biomolecule-responsive hydrogels are a potentially promising tool for user-friendly early diagnostics and on-demand drug-releasing soft materials. We expect that our rational design strategies for stimuli-responsive supramolecular hydrogels by modification of chemical structures and hybridization with functional materials will inspire scientists in various fields and lead to development of novel soft materials for biological applications.

Dual-responsive aggregation-induced emission-active supramolecular nanoparticles for gene delivery and bioimaging

Dual-responsive aggregation-induced emission-active supramolecular nanoparticles exhibit a unique morphological transition with fluorescence variation, further achieving efficient gene delivery and bioimaging.

Supramolecular Hydrogelators and Hydrogels: From Soft Matter to Molecular Biomaterials

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 address fundamental questions about the mechanisms or the consequences of the self-assembly of molecules, including low molecular weight ones. Finally, we provide a perspective on supramolecular hydrogelators. We hope that this review will serve as an updated introduction and reference for researchers who are interested in exploring supramolecular hydrogelators as molecular biomaterials for addressing the societal needs at various frontiers.

Multifarious facets of sugar-derived molecular gels: molecular features, mechanisms of self-assembly and emerging applications

The remarkable capability of nature to design and create excellent self-assembled nano-structures, especially in the biological world, has motivated chemists to mimic such systems with synthetic molecular and supramolecular systems. The hierarchically organized self-assembly of low molecular weight gelators (LMWGs) based on non-covalent interactions has been proven to be a useful tool in the development of well-defined nanostructures. Among these, the self-assembly of sugar-derived LMWGs has received immense attention because of their propensity to furnish biocompatible, hierarchical, supramolecular architectures that are macroscopically expressed in gel formation. This review sheds light on various aspects of sugar-derived LMWGs, uncovering their mechanisms of gelation, structural analysis, and tailorable properties, and their diverse applications such as stimuli-responsiveness, sensing, self-healing, environmental problems, and nano and biomaterials synthesis.

pH-Sensitive polymer assisted self-aggregation of bis(pyrene) in living cells in situ with turn-on fluorescence

Supramolecular self-assemblies with various nanostructures in organic and aqueous solutions have been prepared with desired functions. However, in situ construction of self-assembled superstructures in physiological conditions to achieve expected biological functions remains a challenge. Here, we report a supramolecular system to realize the in situ formation of nanoaggregates in living cells. The bis(pyrene) monomers were dispersed inside of hydrophobic domains of pH-sensitive polymeric micelles and delivered to the lysosomes of cells. In the acidic lysosomes, the bis(pyrene) monomers were released and self-aggregated with turn-on fluorescence. We envision this strategy for in situ construction of supramolecular nanostructures in living cells will pave the way for molecular diagnostics in the future.

Recent advances in the development of synthetic chemical probes for glycosidase enzymes

The emergence of synthetic glycoconjugates as chemical probes for the detection of glycosidase enzymes has resulted in the development of a range of useful chemical tools with applications in glycobiology, biotechnology, medical and industrial research. Critical to the function of these probes is the preparation of substrates containing a glycosidic linkage that when activated by a specific enzyme or group of enzymes, irreversibly releases a reporter molecule that can be detected. Starting from the earliest examples of colourimetric probes, increasingly sensitive and sophisticated substrates have been reported. In this review we present an overview of the recent advances in this field, covering an array of strategies including chromogenic and fluorogenic substrates, lanthanide complexes, gels and nanoparticles. The applications of these substrates for the detection of various glycosidases and the scope and limitations for each approach are discussed.

Supramolecular hydrogels: synthesis, properties and their biomedical applications

As a novel class of three-dimensional (3D) hydrophilic cross-linked polymers, supramolecular hydrogels not only display unique physicochemical properties (e.g., water-retention ability, drug loading capacity, biodegradability and biocompatibility, biostability) as well as specific functionalities (e.g., optoelectronic properties, bioactivity, self-healing ability, shape memory ability), but also have the capability to undergo reversible gel-sol transition in response to various environmental stimuli inherent to the noncovalent cross-linkages, thereby showing great potential as promising biomaterial scaffolds for diagnosis and therapy. In this Review, we summarized the recent progress in the design and synthesis of supramolecular hydrogels through specific, directional noncovalent interactions, with particular emphasis on the structure-property relationship, as well as their wide-ranging applications in disease diagnosis and therapy including bioimaging, biodetection, therapeutic delivery, and tissue engineering. We believe that these current achievements in supramolecular hydrogels will greatly stimulate new ideas and inspire persistent efforts in this hot topic area in future.

Bent π-conjugated systems composed of three-dimensional benzoannulenes

This article describes bent π-conjugated systems composed of alternating o-phenylene and Z-vinylene units. all-Z-[n]Benzo[4n]annulenes are higher homologues of dibenzocyclooctatetraene (DBCOT) with a concave π system, and attempts were made to convert [20]- and [24]annulenes having partial belt structures of fullerenes and carbon nanotubes into [10]- and [12]phenacenes. A bent π-conjugated system composed of two DBCOT units showed dynamic syn-anti equilibrium in solution and behaved as dynamic molecular tweezers (DMTs). The syn isomers of the DMTs formed blue charge-transfer complexes with DDQ in solution, and this complexation and color change were applied to thermochromism. Furthermore, DMTs having two CN groups on each COT ring exhibited crystalline-state emission in the presence of solvent molecules, although almost no emission was observed in solution or the solid state. Based on this crystalline-state emission, a vapochromic system was established. The multifunctional properties of DMTs caused by the flexibility of the nonplanar π system are summarized.

Long-chain alkylamide-derived oil gels: mixing induced onset of thixotropy and application in sustained drug release

Oil gels composed of long-chain alkylamides exhibited thixotropic properties, although the same property was absent in each alkylamide.

Multi-responsive supramolecular hydrogels for drug delivery

We reported a versatile method to prepare responsive supramolecular hydrogels.

Nanoarchitectonics of biomolecular assemblies for functional applications

The stringent processes of natural selection and evolution have enabled extraordinary structure-function properties of biomolecules. Specifically, the archetypal designs of biomolecules, such as amino acids, nucleobases, carbohydrates and lipids amongst others, encode unparalleled information, selectivity and specificity. The integration of biomolecules either with functional molecules or with an embodied functionality ensures an eclectic approach for novel and advanced nanotechnological applications ranging from electronics to biomedicine, besides bright prospects in systems chemistry and synthetic biology. Given this intriguing scenario, our feature article intends to shed light on the emerging field of functional biomolecular engineering.

Synthesis of novel conjugates of a saccharide, amino acids, nucleobase and the evaluation of their cell compatibility

This article reports the synthesis of a novel type of conjugate of three fundamental biological build blocks (i.e., saccharide, amino acids, and nucleobase) and their cell compatibility. The facile synthesis starts with the synthesis of nucleobase and saccharide derivatives, then uses solid-phase peptide synthesis (SPPS) to build the peptide segment (Phe-Arg-Gly-Asp or naphthAla-Phe-Arg-Gly-Asp with fully protected groups), and later, an amidation reaction in liquid phase connects these three parts together. The overall yield of these multiple step synthesis is about 34%. Besides exhibiting excellent solubility, these conjugates of saccharide-amino acids-nucleobase (SAN), like the previously reported conjugates of nucleobase-amino acids-saccharide (NAS) and nucleobase-saccharide-amino acids (NSA), are mammalian cell compatible.

L-Rhamnose-containing supramolecular nanofibrils as potential immunosuppressive materials

An l-rhamnose-based hydrogelator self-assembles to form nanofibrils, which, in contrast to the properties of monomeric l-rhamnose, suppress the antibody response of mice to phycoerythrin (PE), a fluorescent protein antigen. As the first example of the supramolecular assemblies of a saccharide to suppress immunity, this work illustrates a new approach of immunomodulation.

Cellular membrane enrichment of self-assembling D-peptides for cell surface engineering

We occasionally found that several self-assembling peptides containing D-amino acids would be preferentially enriched in cellular membranes at self-assembled stages while distributed evenly in the cytoplasma of cells at unassembled stages. Self-assembling peptides containing only Lamino acids distributed evenly in cytoplasma of cells at both self-assembled and unassembled stages. The self-assembling peptides containing D-amino acids could therefore be applied for engineering cell surface with peptides. More importantly, by integrating a protein binding peptide (a PDZ domain binding hexapeptide of WRESAI) with the self-assembling peptide containing D-amino acids, protein could also be introduced to the cell surface. This study not only provided a novel approach to engineer cell surface, but also highlighted the unusual properties and potential applications of self-assembling peptides containing D-amino acids in regenerative medicine, drug delivery, and tissue engineering.

N-Alkylamido-d-glucamine-based gelators for the generation of thixotropic gels

Hydrogels made from new gelators exhibit thixotropic properties, whereas hydrogels formed with structurally similar N-alkyl-d-glucamide have a tendency to crystallize.

Onset of mixing-induced thixotropy in hydrogels by mixing two homologues of low-molecular-weight hydrogelators

We determined the onset of thixotropy in hydrogels when two homologues of low-molecular-weight hydrogelators, N-alkyl-d-glucamides (CnNG), were mixed.

Enzyme-instructed self-assembly of hydrogelators consisting of nucleobases, amino acids, and saccharide

We report the first example of the use of enzymes to trigger the self-assembly of the conjugates of nucleobases, amino acids, and saccharide to form supramolecular hydrogels in water, which illustrates a facile approach for the development of a new class of multifunctional soft materials for biomedical applications.

A new composite thixotropic hydrogel composed of a low-molecular-weight hydrogelator and a nanosheet

New composite comprised of low-molecular-weight hydrogelator and the nanosheet Laponite®, showed thixotropic behaviour.

Self-assembly of novel benzimidazole N-glycosylamines into nanofibers and nanospheres

Cu²⁺ ions induce the change in the morphology of self-assembled benzimidazole N-glycosylamines from nano-fibers to nano-spheres.