Guanosine-5'-Monophosphate Polyamine Hybrid Hydrogels: Enhanced Gel Strength Probed by z-Spectroscopy

Advanced Binary Guanosine and Guanosine 5'-Monophosphate Cell-Laden Hydrogels for Soft Tissue Reconstruction by 3D Bioprinting

Soft tissue defects or pathologies frequently necessitate the use of biomaterials that provide the volume required for subsequent vascularization and tissue formation as autrografts are not always a feasible alternative. Supramolecular hydrogels represent promising candidates because of their 3D structure, which resembles the native extracellular matrix, and their capacity to entrap and sustain living cells. Guanosine-based hydrogels have emerged as prime candidates in recent years since the nucleoside self-assembles into well-ordered structures like G-quadruplexes by coordinating K⁺ ions and π-π stacking, ultimately forming an extensive nanofibrillar network. However, such compositions were frequently inappropriate for 3D printing due to material spreading and low shape stability over time. Thus, the present work aimed to develop a binary cell-laden hydrogel capable of ensuring cell survival while providing enough stability to ensure scaffold biointegration during soft tissue reconstruction. For that purpose, a binary hydrogel made of guanosine and guanosine 5'-monophosphate was optimized, rat mesenchymal stem cells were entrapped, and the composition was bioprinted. To further increase stability, the printed structure was coated with hyperbranched polyethylenimine. Scanning electron microscopic studies demonstrated an extensive nanofibrillar network, indicating excellent G-quadruplex formation, and rheological analysis confirmed good printing and thixotropic qualities. Additionally, diffusion tests using fluorescein isothiocyanate labeled-dextran (70, 500, and 2000 kDa) showed that nutrients of various molecular weights may diffuse through the hydrogel scaffold. Finally, cells were evenly distributed throughout the printed scaffold, cell survival was 85% after 21 days, and lipid droplet formation was observed after 7 days under adipogenic conditions, indicating successful differentiation and proper cell functioning. To conclude, such hydrogels may enable the 3D bioprinting of customized scaffolds perfectly matching the respective soft tissue defect, thereby potentially improving the outcome of the tissue reconstruction intervention.

The Bioactivity of Xylene, Pyridine, and Pyrazole Aza Macrocycles against Three Representative Leishmania Species

Due to the urgent need for finding effective and free of secondary effect treatments for every clinical form of Leishmaniasis, a series of synthetic xylene, pyridine and, pyrazole azamacrocycles were tested against three Leishmania species. A total of 14 compounds were tested against J774.2 macrophage cells which were models for host cells, and against promastigote and amastigote forms of each studied Leishmania parasite. Amongst these polyamines, one proved effective against L. donovani, another one for L. braziliensis and L. infantum, and another one was selective solely for L. infantum. These compounds showed leishmanicidal activity and reduced parasite infectivity and dividing ability. Action mechanism studies gave a hint that compounds were active against Leishmania due to their ability to alter parasite metabolic pathways and reduce (except Py33333) parasitic Fe-SOD activity.

Nucleoside-Based Supramolecular Hydrogels: From Synthesis and Structural Properties to Biomedical and Tissue Engineering Applications

Supramolecular hydrogels are of great interest in tissue scaffolding, diagnostics, and drug delivery due to their biocompatibility and stimuli-responsive properties. In particular, nucleosides are promising candidates as building blocks due to their manifold noncovalent interactions and ease of chemical modification. Significant progress in the field has been made over recent years to allow the use of nucleoside-based supramolecular hydrogels in the biomedical field, namely drug delivery and 3D bioprinting. For example, their long-term stability, printability, functionality, and bioactivity have been greatly improved by employing more than one gelator, incorporating different cations, including silver for antibacterial activity, or using additives such as boric acid or even biomolecules. This now permits their use as bioinks for 3D printing to produce cell-laden scaffolds with specified geometries and pore sizes as well as a homogeneous distribution of living cells and bioactive molecules. We have summarized the latest advances in nucleoside-based supramolecular hydrogels. Additionally, we discuss their synthesis, structural properties, and potential applications in tissue engineering and provide an outlook and future perspective on ongoing developments in the field.

All-small-molecule supramolecular hydrogels assembled from guanosine 5'-monophosphate disodium salt and tobramycin for the treatment of bacterial keratitis

Bacterial keratitis is the most common corneal infection which may lead to blindness, and seriously threatened the human visual health worldwide. Clinical treatment with antibiotic eye drops formulation usually falls in low bioavailability and poor therapeutic efficiency. Hydrogel has gained much attention as ophthalmic formulation recently due to the prolonged drug retention on ocular surface. In this study, we proposed a type of all-small-molecule supramolecular hydrogel assembled from guanosine-5′-monophosphate disodium salt and tobramycin for the treatment of bacterial keratitis. Guanosine-5′-monophosphate disodium salt assembled into guanosine-quartet nanofibers via hydrogen bonding and π-π stacking, and tobramycin with five primary amine groups further crosslinked the nanofibers bearing multiple phosphate moieties into gel networks via ionic interactions. The supramolecular gel showed shear thinning and thixotropic properties, good biocompatibility, and antibacterial activity. The gel treatment significantly ameliorated P. aeruginosa induced bacterial keratitis, and showed higher therapeutic efficacy compared to tobramycin eye drop. This study provides a facile and efficient antibiotic gel formulation for clinical treatment of bacterial keratitis.

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A type of all-small-molecule supramolecular hydrogel was assembled from 5′-GMP and tobramycin via ionic interactions.

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The prepared gel showed good transparency, thixotropic property, biocompatibility, and sustained drug release.

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The hydrogel showed higher therapeutic efficacy of P. aeruginosa induced bacterial keratitis compared to tobramycin eye drop.

Construction of Supramolecular Organogel with Circularly Polarized Luminescence by Self-Assembled Guanosine Octamer

Gel formation using guanosine self-assembly is an important process in supramolecular chemistry. Here, we report the stepwise construction of circularly polarized luminescent supramolecular organogels from self-assembled guanosine quadruplexes. A lipophilic guanosine derivative (aldG) is designed and synthesized for the formation of a well-defined G₈-octamer. The diamine linkers are used to connect G₈-octamer units by imine formation to facilitate the construction of the supramolecular gel networks. ¹H NMR experiments show that the pre-assembled aldG₈-octamer remains intact and is crucial for transparent and stiff organogel formation. With extended conjugation, the aldG organogels exhibit strong green fluorescence emission and circularly polarized properties without the assistance of any external fluorescent dyes, suggesting an alternative approach to construct molecular probes for biological and material applications.

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.

Metal ions confinement defines the architecture of G-quartet, G-quadruplex fibrils and their assembly into nematic tactoids

G-quadruplex, assembled from a square array of guanine (G) molecules, is an important structure with crucial biological roles in vivo but also a versatile template for ordered functional materials. Although the understanding of G-quadruplex structures is the focus of numerous studies, little is known regarding the control of G-quartet stacking modes and the spontaneous orientation of G-quadruplex fibrils. Here, the effects of different metal ions and their concentrations on stacking modes of G-quartets are elucidated. Monovalent cations (typically K+) facilitate the formation of G-quadruplex hydrogels with both heteropolar and homopolar stacking modes, showing weak mechanical strength. In contrast, divalent metal ions (Ca2+, Sr2+, and Ba2+) at given concentrations can control G-quartet stacking modes and increase the mechanical rigidity of the resulting hydrogels through ionic bridge effects between divalent ions and borate. We show that for Ca2+ and Ba2+ at suitable concentrations, the assembly of G-quadruplexes results in the establishment of a mesoscopic chirality of the fibrils with a regular left-handed twist. Finally, we report the discovery of nematic tactoids self-assembled from G-quadruplex fibrils characterized by homeotropic fibril alignment with respect to the interface. We use the Frank-Oseen elastic energy and the Rapini-Papoular anisotropic surface energy to rationalize two different configurations of the tactoids. These results deepen our understanding of G-quadruplex structures and G-quadruplex fibrils, paving the way for their use in self-assembly and biomaterials.

G4-quartet hydrogels from 5'-hydrazino-guanosine for the non-covalent and covalent remediation of contaminants from water

The creation of supramolecular hydrogels from relatively simple building blocks demonstrates the power of molecular self-assembly to make functional materials. G4-quartet hydrogels are appealing for a number of applications, including the environmental remediation of pollutants in water. We find that the guanosine analog, 5'-deoxy-5'-hydrazinoguanosine (HG 2) self-assembles into a self-standing hydrogel in the presence of stoichiometric amounts (0.25 equiv.) of KCl. The higher water solubility of HG 2 (14.5 mM), compared to that of the parent compound G 1 (2.1 mM), likely contributes to its enhanced gelation. The structural basis for this HG 2·KCl hydrogel, confirmed by PXRD, IR and CD, is the G4·K+ quartet, which forms extended 1D ion-channel assemblies that entangle to give a stable and long-lived hydrogel. We also find that adding KCl to a saturated solution of HG 2 triggers the generation of colloidal G4·K+ assemblies in situ that selectively and efficiently binds the anionic dye naphthol blue black (NBB) over a cationic dye. In addition to this non-covalent electrostatic binding of anions, the nucleophilic 5'-hydrazino group in the HG 2·KCl hydrogel HG 2 enables the efficient absorption of propionaldehyde from both the gas phase and from water solution via the formation of covalent hydrazone linkages with the gel matrix.

G-Quartet hydrogels for effective cell growth applications

Functional G-quartet hydrogels formed from natural guanosine cross linked with benzene-1,4-diboronic acid and Mg²⁺ support cell growth with no visible signs of gel degradation.