Insights into low molecular mass organic gelators: a focus on drug delivery and tissue engineering applications

New injectable self-assembled hydrogels that promote angiogenesis through a bioactive degradation product

Hydrogels used in regenerative medicine are often designed to allow cellular infiltration, degradation, and neovascularization. Low molecular weight hydrogels (LMWHs), formed by self-assembly via non-covalent interactions, are gaining significant interest because they are soft, easy to use and injectable. We propose LMWHs as suitable body implant materials that can stimulate tissue regeneration. We produced four new LMWHs with molecular entities containing nucleic acid and lipid building blocks and analyzed the foreign body response upon subcutaneous implantation into mice. Despite being infiltrated with macrophages, none of the hydrogels triggered detrimental inflammatory responses. Most macrophages present in the hydrogel-surrounding tissue acquired an immuno-modulatory rather than inflammatory phenotype. Concomitantly, no fibrotic capsule was formed after three weeks. Our glyconucleolipid LMWHs exhibited different degradation kinetics in vivo and in vitro. LMWHs with high angiogenic properties in vivo, were found to release glyconucleoside (glucose covalently linked to thymidine via a triazole moiety) as a common by-product of in vitro LMWH degradation. Chemically synthesized glyconucleoside exhibited angiogenic properties in vitro in scratch assays with monolayers of human endothelial cells and in vivo using the chick chorioallantoic membrane assay. Collectively, LMWHs hold promise as efficient scaffolds for various regenerative applications by displaying good biointegration without causing fibrosis, and by promoting angiogenesis through the release of a pro-angiogenic degradation product. STATEMENT OF SIGNIFICANCE: The main limitations of biomaterials developed in the field of tissue engineering remains their biocompatibility and vascularisation properties. In this context, we developed injectable Low Molecular Weight Hydrogels (LMWH) exhibiting thixotropic (reversible gelation) and thermal reversible properties. LMWH having injectability is of great advantage since it allows for their delivery without wounding the surrounding tissues. The resulting gels aim at forming scaffolds that the host cells colonize without major inflammation, and that won't be insulated by a strong fibrosis reaction. Importantly, their molecular degradation releases a product (a glycosyl-nucleoside conjugate) promoting angiogenesis. In this sense, these LMWH represent an important advance in the development of biomaterials promoting tissue regeneration.

Boron Effect on Sugar-Based Organogelators

The reaction of several alkylglucosides with phenyl boronic acid permitted easy access to a series of alkylglucoside phenyl boronate derivatives. This type of compound has structures similar to those of known benzylidene glucoside organogelators except for the presence of a boronate function in place of the acetal one. Low to very low concentrations of these amphiphilic molecules produced gelation of several organic solvents. The rheological properties of the corresponding soft materials characterized them as elastic solids. They were further characterized by SEM to obtain more information on their morphologies and by SAXS to determine the type of self-assembly involved within the gels. The sensitivity of the boronate function towards hydrolysis was also investigated. We demonstrated that a small amount of water (5 % v/v) was sufficient to disrupt the organogels leading to the original alkylglucoside and phenyl boronic acid; an important difference with the stable benzylidene-based organogelators. Such water-sensitive boronated organogelators could be suitable substances for the preparation of smart soft material for topical drug delivery.

Supramacromolecular injectable hydrogels by crystallization-driven self-assembly of carbohydrate-conjugated poly(2-isopropyloxazoline)s for biomedical applications

An approach for the preparation of self-healing and injectable hydrogels based on the crystallization-driven self-assembly of carbohydrate-conjugated poly(2-isopropyloxazoline)s is reported. Hydrogelation does not require any organic solvents, as the polymers dissolve in water below their lower critical solution temperatures. The transplanted hydrogels cause no significant foreign-body response. Considering the simplicity of the method and the biocompatibility of the resulting injectable hydrogels, crystallization-driven hydrogelation of poly(oxazoline)-based polymers may potentially be used in a wide range of biomedical applications.

Amino Acid-Containing Phase-Selective Organogelators: A Water-Based Delivery System for Oil Spill Treatment

The simple structural modification of replacing a terminal carboxylic acid with a primary amide group was found to lower the minimum gelation concentration (MGC), by at least an order of magnitude, for a series of N-lauroyl-l-amino acid phase-selective organogelators in decane. The amide-functionalized analogue N-lauroyl-l-alanine-CONH₂ was demonstrated to gel a broad range of solvents from diesel to THF at MGCs of 2.5% w/v or less, as well as to produce gels with a higher thermal stability (ca. 30 °C) and enhanced mechanical properties (5 times increase in complex modulus), compared to the carboxylic acid analogue, N-lauroyl-l-alanine-COOH. These improved properties may be due to the additional hydrogen bonding in the primary amide analogue as revealed by SCXRD. Most significantly for this study, the introduction of the primary amide functionality enabled N-lauroyl-l-alanine-CONH₂ to form a self-assembled fibrillar network in water. The aqueous network could then actively uptake and rapidly gel decane, diesel, and diluted bitumen ("dilbit") with MGCs of 2.5% w/v or less. This aqueous delivery method is advantageous for oil-remediation applications as no harmful carrier solvents are required and the gel can be easily separated from the water, allowing the oil to be recovered and the gelator recycled.

Hybrid GMP-polyamine hydrogels as new biocompatible materials for drug encapsulation

Here we present the preparation and characterization of new biocompatible materials for drug encapsulation. These new gels are based on positively charged [1+1] 1H-pyrazole-based azamacrocycles which minimise the electrostatic repulsions between the negatively charged GMP molecules. Rheological measurements confirm the electroneutral hydrogel structure as the most stable for all the GMP-polyamine systems. Nuclear magnetic resonance (NMR) was employed to investigate the kinetics of the hydrogel formation and cryo-scanning electron microscopy (cryo-SEM) was used to obtain information about the hydrogel morphology, which exhibited a non-homogeneous structure with a high degree of cross-linking. It is possible to introduce isoniazid, which is the most employed antibiotic for tuberculosis treatment, into the hydrogels without disrupting the hydrogel structure at appropriate concentrations for oral administration.

The role of hydrogen bonds in TAG derivative-based oleogel structure and properties

Glycerol monosterate (GMS) and stearic acid (SA) share a similar carbon chain structure while SA has a carboxyl head group and GMS has two free hydroxyl groups. The current research focuses on the relationship between GMS and SA chemical structure, nano and mesoscale crystal structure, and the oleogel macroscopic characteristics. Molecular analysis revealed the formation of different types of hydrogen bonds, which disappear upon temperature increase at different temperatures. Nano-structural analysis exhibited tight and ordered lamellar structures for SA compared with loosely packed short lamellar structures in GMS oleogel, presumably due to its larger hydrophilic head group. Microstructure imaging revealed ordered anisotropically orientated needle-like crystals in SA and isotopically ordered braid-like crystals in GMS oleogels. Mechanical analysis revealed that gel strength is enhanced when crystal structure is isotropically oriented, similar behavior seen is composite materials, where the structuring agent crystals behave like a reinforcing agent within the oil matrix.

Ultrashort Peptide Self-Assembly: Front-Runners to Transport Drug and Gene Cargos

The translational therapies to promote interaction between cell and signal come with stringent eligibility criteria. The chemically defined, hierarchically organized, and simpler yet blessed with robust intermolecular association, the peptides, are privileged to make the cut-off for sensing the cell-signal for biologics delivery and tissue engineering. The signature service and insoluble network formation of the peptide self-assemblies as hydrogels have drawn a spell of research activity among the scientists all around the globe in the past decades. The therapeutic peptide market players are anticipating promising growth opportunities due to the ample technological advancements in this field. The presence of the other organic moieties, enzyme substrates and well-established protecting groups like Fmoc and Boc etc., bring the best of both worlds. Since the large sequences of peptides severely limit the purification and their isolation, this article reviews the account of last 5 years' efforts on novel approaches for formulation and development of single molecule amino acids, ultra-short peptide self-assemblies (di- and tri- peptides only) and their derivatives as drug/gene carriers and tissue-engineering systems.

Sustainable sorbitol-derived compounds for gelation of the full range of ethanol-water mixtures

During the development of soft material systems inspired by green chemistry, we show that naturally occurring starting materials can be used to prepare mono- and di-benzylidene sorbitol derivatives. These compounds gelate a range of organic, aqueous (including with mono and divalent metal salt solutions) and ethanolic (ethanol-water) solutions, with the equimolar mixture of two of the gelators gelling all compositions from 100% ethanol to 100% water (something neither of the individual components do). We explored the influence of modifications to the acetal substituents on the formation of the compounds as well as the impact of steric bulk on self-assembly properties of the gelators. The effect of solvent on the self-assembly, morphology, and rheology of the 1,3:2,4-di(4-isopropylbenzylidene)-d-sorbitol (DBS-iPr), 2,4(4-isopropylbenzylidene)-d-sorbitol (MBS-iPr) and the equimolar multicomponent (DBS-MBS-iPr) gels have been investigated. DBS-iPr gelates polar solvents to form smooth flat fibres, whereas in non-polar solvents such as cyclohexane helical fibres grow where the chirality is determined by the stereochemistry of the sugar. Oscillatory rheology revealed that MBS-iPr gels have appreciable strength and elasticity, in comparison to DBS-iPr gels, regardless of the solvent medium employed. Powder X-ray diffraction was used to probe the arrangement of the gelators in the xerogels they form, and two single crystal X-ray structures of related MBS derivatives give the first precise structural information concerning layering and hydrogen bonding in the monobenzylidene compounds. This kind of layering could explain the apparent self-sorting behaviour of the DBS-MBS-iPr multicomponent gels. The combination of sorbitol-derived gelators reported in this work could find potential applications as multicomponent systems, for example, in soft materials for personal care products, polymer nucleation/clarification, and energy technology.

Recent advances in coordination-driven polymeric gel materials: design and applications

Recently, research attention has been directed towards the coordination driven synthesis of gels, including coordination polymer gels (CPGs) and metal-organic cage based gels, which have shown applications in diverse fields, including optoelectronics, catalysis, sensing, gas-storage, and self-healing. A wide variety of CPGs and metal-organic cage based gels have been reported, to date, by choosing the right combination of metal ions and rationally designed organic linkers. In this article, we focused on recent developments in CPGs and metal-organic cage based gels and their applications.

Novel Class of Isoxazole-Based Gelators for the Separation of Bisphenol A from Water and Cleanup of Oil Spills

A series of low-molecular-weight gelators based on an isoxazole backbone were synthesized, which showed robust and phase-selective gelation of a series of oils. Due to their excellent phase-selective and cogelation properties, they were employed for the separation of bisphenol and the recovery of oil spills from water. The driving force and morphology of these gels were characterized by spectroscopic and microscopic studies.

New Developments in Medical Applications of Hybrid Hydrogels Containing Natural Polymers

New trends in biomedical applications of the hybrid polymeric hydrogels, obtained by combining natural polymers with synthetic ones, have been reviewed. Homopolysaccharides, heteropolysaccharides, as well as polypeptides, proteins and nucleic acids, are presented from the point of view of their ability to form hydrogels with synthetic polymers, the preparation procedures for polymeric organic hybrid hydrogels, general physico-chemical properties and main biomedical applications (i.e., tissue engineering, wound dressing, drug delivery, etc.).

Silver-Nanoparticles Embedded Pyridine-Cholesterol Xerogels as Highly Efficient Catalysts for 4-Nitrophenol Reduction

Two xerogels made of 4-pyridyl cholesterol (PC) and silver-nanocomposites (SNCs) thereof have been studied for their efficient reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in the presence of aqueous sodium borohydride. Since in-situ silver doping will be effective in ethanol and acetone solvents with a PC gelator, two silver-loaded PC xerogels were prepared and successive SNCs were achieved by using an environmentally benign trisodium citrate dehydrate reducing agent. The formed PC xerogels and their SNCs were comprehensively investigated using different physico-chemical techniques, such as field emission scanning electron microscopy (FE-SEM), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), powdered X-ray diffraction (XRD) and UV-Visible spectroscopy (UV-Vis). The FE-SEM results confirm that the shape of xerogel-covered silver nanoparticles (SNPs) are roughly spherical, with an average size in the range of 30–80 nm. Thermal degradation studies were analyzed via the sensitive graphical Broido’s method using a TGA technique. Both SNC-PC (SNC-PC-X1 and SNC-PC-X2) xerogels showed remarkable catalytic performances, with recyclable conversion efficiency of around 82% after the fourth consecutive run. The apparent rate constant (k_app) of SNC-PC-X1 and SNC-PC-X2 were found to be 6.120 × 10^-3 sec^-1 and 3.758 × 10^-3 sec^-1, respectively, at an ambient temperature.

Preparation and characterization of a supramolecular hydrogel made of phospholipids and oleic acid with a high water content

A hydrogel formed with phospholipids and fatty acids would be of great interest in the medical field due to the biological relevance that these molecules have in living organisms. However, the tendency of phospholipid mixtures to form vesicular or micellar aggregates at high water content hinders the formation of this type of hydrogel. In this study, a highly hydrated hydrogel (95% water) was formed with hydrogenated phosphatidylcholine and oleic acid. The preparation method involved a freeze-heating cycle of the aqueous lipid mixture, favouring the supramolecular aggregation of these molecules into a microscopic spongy morphology. Confocal fluorescence imaging showed that the microstructure of the hydrogel is made from the aggregation of giant multilamellar vesicles (5-20 μm diameter) while transmission electron microscopy revealed the existence of nanosized unilamellar vesicles (150 nm diameter) coexisting with lipid lamellae. Despite this type of aggregation, X-ray scattering experiments performed on the hydrogel show almost no correlation between lipid membranes. In terms of rheological properties, the material shows a prevalent elastic behaviour and low structural strength, a consequence of non-covalent interactions. With such properties and composition, this structured but easily deformable material might become a useful tool for biomedical applications.

Self-Assembling Supramolecular Hybrid Hydrogel Beads

With the goal of imposing shape and structure on supramolecular gels, we combine a low-molecular-weight gelator (LMWG) with the polymer gelator (PG) calcium alginate in a hybrid hydrogel. By imposing thermal and temporal control of the orthogonal gelation methods, the system either forms an extended interpenetrating network or core-shell-structured gel beads-a rare example of a supramolecular gel formulated inside discrete gel spheres. The self-assembled LMWG retains its unique properties within the beads, such as remediating PdII and reducing it in situ to yield catalytically active Pd0 nanoparticles. A single PdNP-loaded gel bead can catalyse the Suzuki-Miyaura reaction, constituting a simple and easy-to-use reaction-dosing form. These uniquely shaped and structured LMWG-filled gel beads are a versatile platform technology with great potential in a range of applications.

Retracted Article: A self-assembled supramolecular natural product gel from liquidambaric acid in traditional Chinese medicine with inherent anti-inflammatory activity for drug delivery

A supramolecular self-assembled natural product gel from liquidambaric acid in traditional Chinese medicine with inherent anti-inflammatory activity for drug delivery was constructed.

Molecular dynamics based descriptors for predicting supramolecular gelation

Four molecular dynamics-based descriptors were derived able to classify gelator–solvent combinations as a gel, precipitate or clear solution.

Mechanistic investigations into the encapsulation and release of small molecules and proteins from a supramolecular nucleoside gel in vitro and in vivo

Supramolecular gels have recently emerged as promising biomaterials for the delivery of a wide range of bioactive molecules, from small hydrophobic drugs to large biomolecules such as proteins. Although it has been demonstrated that each encapsulated molecule has a different release profile from the hydrogel, so far diffusion and steric impediment have been identified as the only mechanisms for the release of molecules from supramolecular gels. Erosion of a supramolecular gel has not yet been reported to contribute to the release profiles of encapsulated molecules. Here, we use a novel nucleoside-based supramolecular gel as a drug delivery system for proteins with different properties and a hydrophobic dye and describe for the first time how these materials interact, encapsulate and eventually release bioactive molecules through an erosion-based process. Through fluorescence microscopy and spectroscopy as well as small angle X-ray scattering, we show that the encapsulated molecules directly interact with the hydrogel fibres - rather than being physically entrapped in the gel network. The ability of these materials to protect proteins against enzymatic degradation is also demonstrated here for the first time. In addition, the released proteins were proven to be functional in vitro. Real-time fluorescence microscopy together with macroscopic release studies confirm that erosion is the key release mechanism. In vivo, the gel completely degrades after two weeks and no signs of inflammation are detected, demonstrating its in vivo safety. By establishing the contribution of erosion as a key driving force behind the release of bioactive molecules from supramolecular gels, this work provides mechanistic insight into the way molecules with different properties are encapsulated and released from a nucleoside-based supramolecular gel and sets the basis for the design of more tailored supramolecular gels for drug delivery applications.

High-performance poly(acrylic acid) hydrogels formed with a block copolymer crosslinker containing amino-acid derivatives

Two block copolymers containing two amino-acid derivatives, PEO-b-PLAA and PEO-b-PAAC, were fabricated through atom transfer radical polymerization (ATRP) or reversible addition-fragmentation chain transfer polymerization (RAFT). Then, they were employed as a macro-crosslinker to prepare high-performance poly(acrylic acid) (PAA) hydrogels named "PxAy" or "TyAz". There were numerous synergistic noncovalent interactions with hydrogen bonds between the macro-crosslinker and PAA chains, as well as entanglement of polymer chains. Hence, the hydrogels exhibited desirable mechanical properties and self-healing abilities. For PxAy hydrogels, the maximum fracture elongation and fracture strength were 9800% and 120.01 kPa, respectively. Moreover, the enhanced physical interaction enabled the hydrogels to have rapid self-healing abilities without stimulation. The hydrogels showed >80% self-healing efficiency and exhibited ∼10-3 S cm-1 electrical conductivity upon the introduction of KCl. Meanwhile, benefitting from doubling the number of carboxyl groups in the macro-crosslinker of the TyAz hydrogels compared with the PxAy hydrogels, the mechanical properties of TyAz hydrogels could be promoted further and notch-insensitivity could be observed. Tough, adhesive, self-healable, and conductive PAA hydrogels with different structures of amino-acid derivatives could aid the development of macro-crosslinkers.

Solvent-Assisted Tyrosine-Based Dipeptide Forms Low-Molecular Weight Gel: Preparation and Its Potential Use in Dye Removal and Oil Spillage Separation from Water

Low-molecular weight gelators (supramolecular, or simply molecular gels) are highly important molecular frameworks because of their potential application in drug delivery, catalysis, pollutant removal, sensing materials, and so forth. Herein, a small dipeptide composed of N-(tert-butoxycarbonyl)pentafluoro-l-phenylalanine and O-benzyl-l-tyrosine methyl ester was synthesized, and its gelation ability was investigated in different solvent systems. It was found that the dipeptide was unable to form gel with a single solvent, but a mixture of solvent systems was found to be suitable for the gelation of this dipeptide. Interestingly, water was found to be essential for gelation with the polar protic solvent, and long-chain hydrocarbon units such as, petroleum ether, kerosene, and diesel, were important for gelation with aromatic solvents. The structural insights of these gels were characterized by field-emission scanning electronic microscopy, atomic force microscopy, Fourier transform infrared analysis, and X-ray diffraction studies, and their mechanical strengths were characterized by rheological experiments. Both of the gels obtained from these two solvent systems were thermoreversible in nature, and these translucent gels had potential application for the treatment of waste water. The gel obtained from dipeptides with methanol-water was used to remove toxic dyes (crystal violet, Eriochrome Black T, and rhodamine B) from water. Furthermore, the gel obtained from dipeptide with assistance from toluene-petroleum ether was used as a phase-selective gelator for oil-spill recovery.

Wet spinning and radial self-assembly of a carbohydrate low molecular weight gelator into well organized hydrogel filaments

In this work, we describe how a simple single low molecular weight gelator (LMWG) molecule - N-heptyl-d-galactonamide, which is easy to produce at the gram scale - is spun into gel filaments by a wet spinning process based on solvent exchange. A solution of the gelator in DMSO is injected into water and the solvent diffusion triggers the supramolecular self-assembly of the N-heptyl-d-galactonamide molecules into nanometric fibers. These fibers entrap around 97% of water, thus forming a highly hydrated hydrogel filament, deposited in a well organized coil and locally aligned. This self-assembly mechanism also leads to a very narrow distribution of the supramolecular fiber width, around 150 nm. In addition, the self-assembled fibers are oriented radially inside the wet-spun filaments and at a high flow rate, fibers are organized in spirals. As a result, this process gives rise to a high control of the gelator self-assembly compared with the usual thermal sol-gel transition. This method also opens the way to the controlled extrusion at room temperature of these very simple, soft, biocompatible but delicate hydrogels. The gelator concentration and the flow rates leading to the formation of the gel filaments have been screened. The filament diameter, its internal morphology, the solvent exchange and the velocity of the jet have been investigated by video image analysis and electron microscopy. The stability of these delicate hydrogel ropes has been studied, revealing a polymorphic transformation into macroscopic crystals with time under some storage conditions. The cell viability of a neuronal cell line on the filaments has also been estimated.

Amyloid-like peptide nanofibrils as scaffolds for tissue engineering: Progress and challenges (Review)

Networks of amyloid-like nanofibrils assembled from short peptide sequences have the ability to form scaffolds that can encapsulate clinically relevant stem cells encouraging their attachment, growth, and differentiation into various lineages which can be used in tissue engineering applications to treat a range of diseases and traumas. In this review, the author highlights a selection of important proof-of-principle papers that show how this class of self-assembled networks is highly suited to biomaterial scaffold development. The author highlights recent studies which have shown that these scaffolds can be used to promote cell and tissue regeneration both in vitro and in vivo. The author also presents some fundamental knowledge gaps which are preventing the widespread translation of such scaffolds. Finally, the author outlines a selection of studies that elucidate molecular assembly mechanisms and biophysical properties of amyloid-like peptide nanofibrils and suggests how studies like these might lead to the ability to generate nanofibril scaffolds with bespoke properties for tissue engineering.

Theoretical and experimental studies of an oseltamivir-triazole-based thermoresponsive organogel

Low-molecular weight organic gelators have been of significant interest in recent years because of their interesting properties and potential applications in sensing technology, biomedicine and drug delivery. Herein, the synthesis, characterization and gelation properties of new oseltamivir conjugates are reported. The oseltamivir-triazole conjugate 1 was synthesized via a click-reaction in a 75% yield. The key features of this conjugate include the presence of amide, flexible ester linkages and a triazole scaffold linking a hydrophobic alkyl chain. The conjugate 1, possessing a long alkyl chain, showed gelation properties in various apolar organic solvents. This gelation behavior was not observed in the case of the deesterified conjugate 2; this indicated the necessity of the alkyl chain for gelation. The gelator 1 showed thermoreversible gelation properties in a range of linear alkane solvents (from n-pentane to n-dodecane). A scanning electron microscopic study suggests that the gelator 1 exists as cross-linked structures, which are self-aggregated in the range of submicrometers, as supported by extensive ¹H-NMR studies. The rheological parameters supported the occurrence of a soft gelation process, and the gel formed in n-decane was found to be stiffer than that formed in n-hexane. Computational studies suggested that the gelation behavior was indeed due to micelle formation and dependent on the lipophilicity of solvents.

Robust scalable synthesis of a bis-urea derivative forming thixotropic and cytocompatible supramolecular hydrogels

Synthetic hydrogels address a need for affordable, industrially scalable scaffolds for tissue engineering. Herein, a novel low molecular weight gelator is reported that forms self-healing supramolecular hydrogels. Its robust synthesis can be performed in a solvent-free manner using ball milling. Strikingly, encapsulated cells spread and proliferate without specific cell adhesion ligands in the nanofibrous material.

The Development and Lifetime Stability Improvement of Guanosine-Based Supramolecular Hydrogels through Optimized Structure

Guanosine is an important building block for supramolecular gels owing to the unique self-assembly property that results from the unique hydrogen bond acceptors and donor groups. Guanosine-derived supramolecular hydrogels have promise in the fields of drug delivery, targeted release, tissue engineering applications, etc. However, the property of poor longevity and the need for excess cations hinder the widespread applications of guanosine hydrogels. Although guanosine-derived supramolecular hydrogels have been reviewed previously by Dash et al., the structural framework of this review is different, as the modification of guanosine is described at the molecular level. In this review, we summarize the development and lifetime stability improvement of guanosine-based supramolecular hydrogels through optimized structure and elaborate on three aspects: sugar modification, base modification, and binary gels. Additionally, we introduce the concept and recent research progress of self-healing gels, providing inspiration for the development of guanosine-derived supramolecular hydrogels with longer lifespans, unique physicochemical properties, and biological activities.

Nanostructured supramolecular hydrogels: Towards the topical treatment of Psoriasis and other skin diseases

Supramolecular hydrogels were synthesized using a bis-imidazolium based amphiphile, and incorporating chemically diverse drugs, such as the cytostatics gemcitabine hydrochloride and methotrexate sodium salt, the immunosuppressive drug tacrolimus, as well as the corticoid drugs betamethasone 17-valerate and triamcinolone acetonide, and their potential as drug delivery agents in the dermal treatment of Psoriasis was evaluated. The rheological behavior of gels was studied, showing in all cases suitable viscoelastic properties for topical drug delivery. Scanning electron microscopy (SEM) shows that the drugs included have a great influence on the gel morphology at the microscopic level, as the incorporation of gemcitabine hydrochloride leads to slightly thicker fibers, the incorporation of tacrolimus induces flocculation and spherical precipitates, and the incorporation of methotrexate forms curled fibers. ¹H NMR spectroscopy experiments show that these drugs not only remain dissolved at the interstitial space, but up to 72% of either gemcitabine or methotrexate, and up to 38% of tacrolimus, is retained within the gel fibers in gels formed with a 1:1 gelator:drug molar ratio. This unique fiber incorporation not only protects the drug from degradation, but also importantly induces a Two Phase Exponential drug release, where the first phase corresponds to the drug dissolved in the interstitial space, while the second phase corresponds to the drug exiting from the gel fibers, and where the speed in each phase is in accordance with the physicochemical properties of the drugs, opening perspectives for controlled delivery. Skin permeation ex vivo tests show how these gels successfully promote the drug permeation and retention inside the skin for reaching their therapeutic target, while in vivo experiments demonstrate that they decrease the hyperplasia and reduce the macroscopic tissue damage typically observed in psoriatic skin, significantly more than the drugs in solution. All these characteristics, beside the spontaneous and easy preparation (room temperature and soft stirring), make these gels a good alternative to other routes of administration for Psoriasis treatment, increasing the drug concentration at the target tissue, and minimizing side effects.

Synthesis and Characterization of Polyhydroxyalkanoate Organo/Hydrogels

Synthetic organogels/hydrogels are attracting growing interests due to their potential applications in biomedical fields, organic electronics, and photovoltaics. Photogelation methods for synthesis of organogels/hydrogels have been shown particularly promising because of the high efficiency and simple synthetic procedures. This study synthesized new biodegradable polyhydroxyalkanoates (PHA)-based organogels/hydrogels via UV photo-cross-linking using unsaturated PHA copolymer poly[(R)-3-hydroxyundecanoate-co-(R)-3-hydroxy-10-undecenoate] (PHU10U) with polyethylene glycol dithiol (PDT) as a photo-cross-linker. The PHU10U was synthesized by an engineered Pseudomonas entomophila and characterized via Fourier transform infrared spectroscopy, ¹H nuclear magnetic resonance (NMR), and ¹³C NMR. With decreasing the molar ratio of PHU10U to PDT, both the swelling ratio and pore size were decreased. Meanwhile, increasing densities of the gel networks resulted in a higher compressive modulus. Cell cytotoxicity studies based on the CCK-8 assay on both the PHU10U precursor and PHU10U/PDT hydrogels showed that the novel PHA-based biodegradables acting as hydrogels possess good biocompatibility.

Exploring the thermal reversibility and tunability of a low molecular weight gelator using vibrational and electronic spectroscopy and rheology

Cationic glycylalanylglycine (GAG) self-assembles into a gel in a 55 mol% ethanol/45 mol% water mixture. The gel exhibits a network of crystalline fibrils grown to lengths on a 10-4-10-5 m scale (Farrel et al., Soft Matter, 2016, 12, 6096-6110). Rheological data are indicative of a rather strong gel with storage moduli in the 10 kPa regime. Spectroscopic data revealed the existence of two gel phases; one forms below T = 15 °C (phase I) while the other one forms in a temperature range between 15 °C and the melting temperature of ca. 35 °C (phase II). We explored the reformation of the cationic GAG gel in 55 mol% ethanol/45 mol% water after thermal annealing by spectroscopic and rheological means. Our data reveal that even a short residence time of 5 minutes in the sol phase at 50 °C produced a delay of the gelation process and a gel of lesser strength. These observations suggest that the residence time at the annealing temperature can be used to adjust the strength of both gel phases. Our spectroscopic data show that the annealing process does not change the chirality of peptide fibrils in the two gel phases and that the initial aggregation state of the reformation process is by far more ordered for phase I than it is for phase II. In the gel phases of GAG/ethanol/water mixtures, ethanol seems to function as a sort of catalyst that enables the self-assembly of the peptide in spite of its low intrinsic propensity for aggregation.

Simple Tyrosine Derivatives Act as Low Molecular Weight Organogelators

The gelation of L-Tyr(tBu)-OH in tetrahydrofuran (THF) was discovered serendipitously. It was noted that this tremendously low molecular weight (LMW) compound has the ability to gel a wide variety of organic solvents (e.g., N,N-Dimetylformamide (DMF), THF, butanol, toluene), even in very low concentrations (i.e., 0.1 wt/v% in DMF). Addition of bases such as NaOH and piperidine enhanced the gel property. By changing the side-chain protecting group to tert-butyldimethylsilyl (TBDMS), a fluoride ion-responsive organogel was also acquired. This new organogelator responded fluoride ion concentration as low as 0.2 ppm. Characterization of microstructures and gel behaviours were studied by powder X-Ray diffraction spectroscopy (XRD), transmission electron microscopy (TEM), rheological measurements and molecular dynamics (MD) simulations. Experimental observations and theoretical simulations consistently show a fibre-like structure of the gel, in which the organogelator molecules are held together via a dense network of hydrogen bonds, and via van der Waals interactions between hydrophobic groups.

Instant hydrogel formation of terpyridine-based complexes triggered by DNA via non-covalent interaction

Biomolecule-based hydrogels have potential use in a wide range of applications such as controlled drug release, tissue engineering, and biofabrication. Herein, driven by specific interactions between ds-DNA (double-stranded DNA) and Zn2+ based metal-complexes, we report that the use of DNA as cross-linkers can enhance interactions between self-assembling Zn2+ complexes containing terpyridine and sugar groups in the generation of bioinspired hydrogels from solutions or suspensions. The gelation process is fast and straightforward without tedious steps and happens at room temperature. Such a hydrogelation process of different Zn2+ complexes endows the visualized and selective DNA analogue discrimination. Several experiments suggest that the strong intercalation binding of Zn2+ complexes with ds-DNA results in the unzipping of ds-DNA into ss-DNA (single-stranded DNA), which further behave as linkers to enhance the intermolecular interactions of self-assembling Zn2+ complex molecules via coordination interactions. This work demonstrates an efficient and universal strategy to prepare hydrogels based on biomolecular recognition. Moreover, the DNA responsive behaviors of Zn2+ complexes are further compared with that of solutions and cells.

Water-Assisted Self-Aggregation of Benzimidazole and Triazole Adducts

The manuscript revolves around an interesting observation of solidification of a solution of N-((1-((1-ethyl-1H-benzo[d]imidazol-2-yl)methyl)-1H-1,2,3-triazole-4-yl)methyl)aniline (A6) in the NMR tube after around 12 h. Real-time images showed fibrillar and spherulitic growth with tip branching and side branching, which is thermoreversible. The compound under investigation is unique because it is synthesized to understand the anticancer activity with two pharmacophores, benzimidazole and triazole. Click chemistry is employed for in situ generation of triazole moiety on benzimidazole. Previously, benzimidazole-based compounds have shown self-aggregation-induced gel-like behavior because of hydrogen bonding and/or π-π stacking interactions. In the present case, NMR titrations with D₂O addition showed two distinct changes in the chemical shift for methylene bridges (connecting benzimidazole and triazole ring) and ortho protons of the phenyl ring (attached to triazole ring). Interestingly, a single-crystal X-ray structure shows the absence of hydrogen bonds and π-π stacking while in the presence of only two distinct close contacts, completely correlating NMR data discussed in detail. A similar "molecular origin" for self-aggregation is observed in seven other flexible but regioisomeric compounds, which were designed and synthesized for inducing hydrogen bonding through the removal of N-ethyl group and insertion of aniline and/or fluoro group.

Perfluoroarene induces a pentapeptidic hydrotrope into a pH-tolerant hydrogel allowing naked eye sensing of Ca2+ ions

Self-assembly of a novel thermoresponsive, pyrene-appended oligopeptide sequence VPGKP (PyP) leads to the formation of spherical aggregates in water. The sizes of the globular aggregates of the peptide, PyP, strongly depend on the temperature of its suspension in water and decrease with the decrease in temperature showing a lower critical solution temperature (LCST) phenomenon. Furthermore, a pyrene-octafluoronaphthalene (OFN) 'pair' has been used as a supramolecular synthon to induce hydrogelation of PyP in the presence of an equimolar amount of OFN via complementary quadrupole-quadrupole interactions. The gel shows excellent pH tolerance and thixotropic behavior. Detailed studies suggest the existence of lamellar packing of the gelators in a right-handed helical fashion which yields globular aggregates. The globular aggregates are sticky in nature and form a gel via inter-globular interactions. Addition of Ca2+ ions reinforces the mechanical strength and also reduces the critical gelator concentration of the native gel through coordination with the free -COO- group of the gelator. Therefore, the present hydrogel system could further be used as a naked eye sensor of Ca2+ ions.

Cytidine and ribothymidine nucleolipids synthesis, organogelation, and selective anion and metal ion responsiveness

Nucleolipids of 2′,3′-O-diacylatedribothymidine supports the organogelation by utilizing inherent self-base pairing and solvent mediated bifurcated H-bonding and hydrophobic effect. These organogels exhibits unusual Hg²⁺ mediated base pairing.

A semiconducting supramolecular Co(ii)-metallohydrogel: an efficient catalyst for single-pot aryl–S bond formation at room temperature

A monoethanolamine based Co(ii)-metallohydrogel can act as a Schottky barrier diode device and a catalyst for single-pot aryl–S bond formation at room temperature.

In situ formation of AuNPs using fatty N-acylamino hydrazide organogelators as templates

This work reports, for the first time, the synthesis of new fatty N-acylamino hydrazides and demonstrates the activity of these compounds as low-molecular-weight organic gelators and templates for preparation of gold nanoparticles (AuNPs).