Formation of gels in the presence of metal ions

Experimental Correlation between Apparent pKa and Gelation Propensity in Amphiphilic Hydrogelators Derived from l-Dopa

We report the gelation propensity of three gelators derived from l-dihydroxyphenylalanine (l-Dopa), where the amino group is derivatized with three different fatty acids (lauric acid, palmitic acid, and azelaic acid). The long aliphatic side chains should introduce additional van der Waals interactions among the molecules, contributing to the self-assembly process. The hydrogels have been prepared with the pH change method, and both the hydrogels and the corresponding aerogels have been analyzed using several techniques. In any case, Lau-Dopa provides stronger hydrogels compared with the other gelators. This property may be ascribed to its tendency to efficiently form supramolecular β-sheet structures, as outlined by the ECD, IR, and SEM analyses. Moreover, the preliminary measurement of the apparent pKa displays for Lau-Dopa two plateaux, as previously observed for, one at about pH 12 and a second one at pH 7.5. Thus, its pKa results in two apparent pKa shifts of ∼8.5 and ∼4 pH units above the theoretical pKa, as a consequence of a multistep self-assembly pathway that correlates, in the final β-sheet-based hydrogel, with a high degree of order and stability.

Delivery of Active Peptides by Self-Healing, Biocompatible and Supramolecular Hydrogels

Supramolecular and biocompatible hydrogels with a tunable pH ranging from 5.5 to 7.6 lead to a wide variety of formulations useful for many different topical applications compatible with the skin pH. An in vitro viability/cytotoxicity test of the gel components demonstrated that they are non-toxic, as the cells continue to proliferate after 48 h. An analysis of the mechanical properties demonstrates that the hydrogels have moderate strength and an excellent linear viscoelastic range with the absence of a proper breaking point, confirmed with thixotropy experiments. Two cosmetic active peptides (Trifluoroacetyl tripeptide-2 and Palmitoyl tripeptide-5) were successfully added to the hydrogels and their transdermal permeation was analysed with Franz diffusion cells. The liquid chromatography-mass spectrometry (HPLC-MS) analyses of the withdrawn samples from the receiving solutions showed that Trifluoroacetyl tripeptide-2 permeated in a considerable amount while almost no transdermal permeation of Palmitoyl tripeptide-5 was observed.

Tuning Mechanical Properties of Pseudopeptide Supramolecular Hydrogels by Graphene Doping

Supramolecular hydrogels, obtained from small organic molecules, may be advantageous over polymeric ones for several applications, because these materials have some peculiar properties that differentiate them from the traditional polymeric hydrogels, such as elasticity, thixotropy, self-healing propensity, and biocompatibility. We report here the preparation of strong supramolecular pseudopeptide-based hydrogels that owe their strength to the introduction of graphene in the gelling mixture. These materials proved to be strong, stable, thermoreversible and elastic. The concentration of the gelator, the degree of graphene doping, and the nature of the trigger are crucial to get hydrogels with the desired properties, where a high storage modulus coexists with a good thixotropic behavior. Finally, NIH-3T3 cells were used to evaluate the cell response to the presence of the most promising hydrogels. The hydrogels biocompatibility remains good, if a small degree of graphene doping is introduced.

Chlorhexidine Gel Use in the Oral District: A Systematic Review

Chlorhexidine compounds and their different formulations have been investigated several times, especially in the dentistry field. Chlorhexidine application for mouth rinsing immediately underwent oral contraindications, linked to the possibility of causing pigmentation to the teeth or relating to possible cytotoxic events after oral surgery. The positive effects, however, are considerable and its topical antiseptic action has been widely demonstrated by in vitro and clinical research. That’s the reason for its large application in different fields of dentistry. The aim of this study is to collect all the literature regarding the use of chlorhexidine gel in dentistry and all the numerous applications. The initial search on search engines obtained 232 results; then, following the application of the inclusion criteria there were 24 selected articles. The chlorhexidine gel appliance in the dental daily practice is direct to oral surgery, conservative endodontics, prevention and prophylaxis. The use of chlorhexidine has shown some positive effects, also in the case of systemic diseases prevention. Surely, this topical medicine used both professionally and prescribed for home use, can be considered a great help for the prevention of several oral pathologies with systemic implications too.

Low Molecular Weight Gelators Based on Functionalized l-Dopa Promote Organogels Formation

We prepared the small pseudopeptide Lau-l-Dopa(OBn)2-d-Oxd-OBn (Lau = lauric acid; l-Dopa = l-3,4-dihydroxyphenylalanine; d-Oxd = (4R,5S)-4-methyl-5-carboxyl-oxazolidin-2-one; Bn = benzyl) through a number of coupling reactions between lauric acid, protected l-Dopa and d-Oxd with an excellent overall yield. The ability of the product to form supramolecular organogels has been tested with different organic solvents of increasing polarity and compared with the results obtained with the small pseudopeptide Fmoc-l-Dopa(OBn)2-d-Oxd-OBn. The mechanical and rheological properties of the organogels demonstrated solvent-dependent properties, with a storage modulus of 82 kPa for the ethanol organogel. Finally, to have a preliminary test of the organogels' ability to adsorb pollutants, we treated a sample of the ethanol organogel with an aqueous solution of Rhodamine B (RhB) for 24 h. The water solution slowly lost its pink color, which became trapped in the organogel.

Biocompatible and Light-Penetrating Hydrogels for Water Decontamination

Solar light-activated photocatalyst nanoparticles (NPs) are promising environment-friendly low cost tools for water decontamination, but their dispersion in the environment must be minimized. Here, we propose the incorporation of TiO₂-NPs (also in combination with graphene platelets) into highly biocompatible hydrogels as a promising approach for the production of photoactive materials for water treatment. We also propose a convenient fluorescence-based method to investigate the hydrogel photocatalytic activity in real time with a conventional fluorimeter. Kinetics analysis of the degradation profile of a target fluorescent model pollutant demonstrates that fast degradation occurs in the matrix bulk. Fluorescence anisotropy proved that small pollutant molecules diffuse freely in the hydrogel. Rheological and scanning electron microscopy characterization showed that the TiO₂-NP incorporation does not significantly alter the hydrogel mechanical and morphological properties.

Thixotropic Peptide-Based Physical Hydrogels Applied to Three-Dimensional Cell Culture

Pseudopeptides containing the d-Oxd or the d-pGlu [Oxd = (4R,5S)-4-methyl-5-carboxyl-oxazolidin-2-one, pGlu = pyroglutamic acid] moiety and selected amino acids were used as low-molecular-weight gelators to prepare strong and thixotropic hydrogels at physiological pH. The addition of calcium chloride to the gelator solutions induces the formation of insoluble salts that get organized in fibers at a pH close to the physiological one. Physical characterization of hydrogels was carried out by morphologic evaluation and rheological measurements and demonstrated that the analyzed hydrogels are thixotropic, as they have the capability to recover their gel-like behavior. As these hydrogels are easily injectable and may be used for regenerative medicine, they were biologically assessed by cell seeding and viability tests. Human gingival fibroblasts were embedded in 2% hydrogels; all of the hydrogels allow the growth of encapsulated cells with a very good viability. The gelator toxicity may be correlated with their tendency to self-assemble and is totally absent when the hydrogel is formed.

The effect ofl-DOPA hydroxyl groups on the formation of supramolecular hydrogels

Fmoc-l-DOPA-d-Oxd-OH was prepared starting from commercially availablel-DOPA. Its gelation ability was tested by comparison with Fmoc-l-Tyr-d-Oxd-OH and Fmoc-l-Phe-d-Oxd-OH using ten different triggers.

Self-healing hydrogels triggered by amino acids

Nine amino acids with different chemical properties have been chosen to promote the formation of hydrogels based on the bolamphiphilic gelator A: three basic amino acids (arginine, histidine and lysine), one acidic amino acid (aspartic acid), two neutral aliphatic amino acids (alanine and serine) and three neutral aromatic amino acids (phenylalanine, tyrosine and tryptophan).

Hydrogelation Induced by Fmoc-Protected Peptidomimetics

Four new low molecular weight hydrogelators (LMWGs) have been prepared in multigram scale and their attitude to form hydrogels has been tested. The gelation trigger is pH variation. The resulting gels have been characterized with several techniques: measurement of the melting points (T(gel)), transparency, gelation time, and viscoelastic properties, together with ECD analysis. Among them, Fmoc-L-Tyr-D-Oxd-OH 1 is an excellent gelator that leads to the preparation of strong, transparent, and viscoelastic gels, by pH variation. UV-visible analyses have demonstrated that the gels obtained with the LMWG 1 possess high transparency, with a transmittance up to 25.6% at a wavelength of 600 nm. Results of the amplitude sweep experiments showed that the elastic response component (G') was approximately an order of magnitude larger than the viscous component, indicating an elastic rather than viscous attitude of the gels, confirmed by the frequency independence of G' and G″ values, in the range from 0.1 to 100 rad·s(-1). The thermal behavior of gel obtained from Fmoc-L-Tyr-D-Oxd-OH 1 was characterized performing an "ad hoc" rheological temperature sweep experiment, that indicated that G' remained almost constant from 23 °C up to about 65 °C while G″ increased in the same temperature range. At higher temperatures, both G' and G″ values started to slightly decrease without displaying a crossover point.

A peptidic hydrogel that may behave as a "Trojan Horse"

A physical hydrogel prepared with the low-molecular-weight hydrogelator (LMWHG) CH₂(C₃H₆CO-L-Phe-D-Oxd-OH)₂ and water/ethanol mixture was applied as a potential “Trojan Horse” carrier into cells. By SEM and XRD analysis we could demonstrate that a fibrous structure is present in the xerogel, making a complex network. The gelator is derived from α-amino acids (Thr, Phe) and a fatty acid (azelaic acid) and is biocompatible: it was dosed to IGROV-1 cells, which internalized it, without significantly affecting the cell proliferation. To check the internalization process by confocal microscopy, fluorescent hydrogels were prepared, introducing the fluorescent dansyl moiety into the mixture.