Self-assembled Gels Research Articles

Probing the self-assembled structures and pKa of hydrogels using electrochemical methods.

The surface chemistry of the aggregated structures that form the scaffold in self-assembled hydrogels - their charge, hydrophobicity and ion-binding dynamics - plays an important role in determining the gel properties and the gel's suitability for specific applications. However, there are limited methods available for the study of this surface chemistry. Here, we show that electrochemical techniques can be used to measure the surface chemical properties of the self-assembled aggregate structures and also to determine the pKa of the gelators. We also provide a method to quickly determine whether a functionalised-dipeptide will form a gel or not. This method has scope for use in high-throughput screening and further complex pH-triggered self-assembled gelation systems.

Tuning gelled lyotropic liquid crystals (LLCs) - probing the influence of different low molecular weight gelators on the phase diagram of the system H2O/NaCl-Genapol LA070.

Gelled lyotropic liquid crystals (LLCs) are highly tunable multi-component materials. By studying a selection of low molecular weight gelators (LMWGs), we find gelators that form self-assembled gels in LLCs without influencing their phase boundaries. We studied the system H2O/NaCl-Genapol LA070 in the presence of (a) the organogelators 12-hydroxyoctadecanoic acid (12-HOA) and 1,3:2,4-dibenzylidene-d-sorbitol (DBS) and (b) the hydrogelators N,N'-dibenzoyl-l-cystine (DBC) and a tris-amido-cyclohexane derivative (HG1). Visual phase studies and oscillation shear frequency sweeps confirmed that 12-HOA acts as co-surfactant (stabilizing the lamellar Lα phase and destabilizing the hexagonal H1 phase), thus preventing gelation. Conversely, DBS was a potent gelator for LLCs, with the phase boundaries un-influenced by the presence of DBS; gelled lamellar Lα, and softly-gelled hexagonal H1 phases are formed. For the hydrogelator DBC, the LLC phase boundaries were only slightly altered, but no gelled LLCs were formed. For the hydrogelator HG1, however, the phase boundaries were unaffected while gelled lamellar Lα and softly-gelled hexagonal H1 phases were formed. Temperature-dependent rheology measurements demonstrated that by changing the DBS or the HG1 concentration, the sol-gel transition temperature of the gelled lamellar Lα phase can be adjusted such that (a) Tsol-gel is below the Lα-isotropic phase transition (DBS, HG1 mass fraction η = 0.0075) and (b) Tsol-gel is above the gelled Lα-isotropic phase transition (DBS, HG1 η = 0.015). This opens the possibility of temporal materials control by addressing phase transitions in different orders. As this system contains oil and water, both the organogelator DBS and the hydrogelator HG1 can gel these LLCs, but this clearly does not apply to all organogelators/hydrogelators. The study indicates that careful optimization of LMWGs is required to avoid interaction with the surfactant layer and to optimize the Tsol-gel value, which is important for the application of LMWGs in gelled LLCs.

An “off–on” fluorescent naphthalimide-based sensor for anions: its application in visual F− and AcO− discrimination in a self-assembled gel state

Herein, we report a novel fluorescent organogelator that could discriminate F− from AcO− in both solution and gel systems.

Al3+ enhanced room temperature phosphorescence of Pd-porphyrin resided in hybrid supramolecular gels and used for detection of trace Hg2+ ions

Micelle-hybridized supramolecular hydrogels were constructed through the self-assembly of gelator N,N-dibenzoyl-L-cystine (DBC) and micelles formed from a Gemini surfactant (G12-8-12). A phosphor, palladium meso-tetra (4-carboxyphenyl) porphyrin (Pd-TCPP) and Al3+ ions were loaded within the hybrid system. Interestingly, the room temperature phosphorescence (RTP) of Pd-TCPP can be efficiently enhanced and modulated by the concentration of Al3+ ions. The enhancement effect could be attributed to the interactions between Al3+ and DBC as well as porphyrin, which verified by 1H NMR analysis. The study of transmission electron microscopy and scanning electron microscopy indicated that a more compact 3D network structure of the gel system was formed upon the addition of Al3+. In addition, measurement of critical micelle concentration indicated that Al3+ ions increase the surface activity of G12-8-12 to promote micelle formation, thereby increasing the dispersion of Pd-TCPP in the hybrid gels. Based on the synergistic effect of these results, the non-radiative transition of Pd-TCPP was efficiently inhibited, resulting in highly efficient RTP. Furthermore, the enhanced RTP of as-prepared gel system shows potential application to detect trace Hg2+ ions because the RTP can be quenched by Hg2+. A linear relationship between RTP against the logarithmic concentration of Hg2+ was found over the range of 6 × 10−8 and 1 × 10−6 mol/L. The detection limit was found to be 0.017 nmol/L.

Thai silk fibroin gelation process enhancing by monohydric and polyhydric alcohols

Silk fibroin hydrogel is an interesting natural material in various biomedical applications. However, the self-assembled gelation takes a long time. In this work, different alcohol types are used as gelation enhancers for aqueous silk fibroin solution. Monohydric alcohols having carbon chain length from C1 to C4 and polyhydric alcohols with the number of mono- to tri- hydroxyl groups were used as the enhancers which are effective for rapid gelation. The addition of monohydric alcohol distinctively reduced the gelation time, comparing to the polyhydric alcohol. The gelation process is directly dependent on the polarity of alcohol and hydrophobicity. The alcohol mediated gelation imparts strong viscoelastic property and enhanced compressive modulus of resulting hydrogels. This is due to the effective formation of self-assembled beta sheet network of the silk fibroin chains facilitates the gelation process.

Self-Assembling Benzothiazole-Based Gelators: A Mechanistic Understanding of in Vitro Bioactivation and Gelation.

Low molecular weight gelators (LMWGs) of chemotherapeutic drugs represent a valid alternative to the existing polymer-based formulations used for targeted delivery of anticancer drugs. Herein we report the design and development of novel self-assembling gelators of the antitumor benzothiazole 5F 203 (1). Two different types of derivatives of 1 were synthesized, formed by an amide (2) and a carbamate (3a-3d) linker, respectively, which showed potent in vitro antitumor activity against MCF-7 mammary and IGROV-1 ovarian carcinoma cells. In contrast, MRC-5 fibroblasts were inherently resistant to the above derivatives (GI50 > 10 μM), thus revealing stark selectivity against the malignant cell lines over the nontransformed fibroblasts. Western blots assays demonstrated induction of CYP1A1 by 1 and its derivatives only in sensitive malignant cells (MCF-7), corroborating conservation of a CYP1A1-mediated mechanism of action. The ability to form stable gels under relatively high strains was supported by rheological tests; in addition, their inner morphology was characterized as possessing a crossed-linked nanostructure, with the formation of thick aggregates with variable widths between 1100 and 400 nm and lengths from 8 to 32 μm. Finally, in vitro dissolution studies proved the ability of hydrogel 2 to release 48% of 2 within 80 h, therefore demonstrating its ability to act as a platform for localized delivery.

A new family of urea-based low molecular-weight organogelators for environmental remediation: the influence of structure.

Gelation processes grant access to a wealth of soft materials with tailorable properties, in applications as diverse as environmental remediation, biomedicine and electronics. Several classes of self-assembling gelators have been studied and employ non-covalent bonds to direct assembly, but recently attention has come to focus on how the overall shape of the gelator molecule impacts its gelation. Here we study a new sub-family of low molecular weight organogelators and explore how steric rearrangement influences their gelation. The gels produced are characterised with X-ray diffraction and small-angle neutron scattering (SANS) to probe their ex situ and in situ gelation mechanisms. The best examples were then tested for environmental remediation applications, gelling petrol and oils in the presence of water and salts.

A versatile method for the selective core-crosslinking of hyaluronic acid nanogels via ketone-hydrazide chemistry: from chemical characterization to in vivo biodistribution.

The development of biopolymer-based nanogels has gained particular interest to achieve successful delivery of therapeutics for the treatment of various diseases, such as cancer, infection and diabetes. Herein, we report a new and simple methodology for the covalent stabilization of self-assembled gel nanoparticles based on hyaluronic acid (HA) modified with a thermoresponsive ketone-functional copolymer. This relies on the selective formation of hydrazone crosslinks with bishydrazides within the globular domains of the copolymer chains formed above the cloud point temperature. This approach allows tuning of the crosslinking density by varying the dihydrazide crosslinker to ketone molar ratio. The size distributions and morphology of the nanogels were assessed using dynamic light scattering (DLS), cryo-transmission and scanning electron microscopy. In vitro cellular uptake in several cancer cells and in vivo biodistribution of the nanogels in different mouse tumor models were then explored to assess the effectiveness of this crosslinking strategy. The data from these experiments show prolonged blood circulation, longer than 24 hours, for the crosslinked nanogels and high tumor accumulation.

Effects of preparation processes on the structure and properties of collagen gel

ABSTRACTIn this study, the effects of collagen self-assembly, drying methods, and reswelling on collagen gel structure and biological properties were determined. The results showed that the self-assembly of collagen improved the regularity and pore size of the collagen gel and promoted collagen gel thermostability and cell proliferation. After drying and reswelling, the main structure of the self-assembly gel was composed of lamellar gel walls, but the gel structure shrank to some extent and pore size was reduced. The structure of the self-assembled gel after drying and reswelling was closely related to that of the drying method.

Partially Acetylated or Benzoylated Arabinose Derivatives as Structurally Simple Organogelators: Effect of the Ester Protecting Group on Gel Properties.

Sugar-based low-molecular-weight gelators (LMWGs) have been used for various applications for a long time. Herein, structurally simple, ester-protected arabinosides are reported as low-molecular-weight organogelators (LMOGs) that are able to gel aromatic solvents, as well as petrol and diesel. Studies on the mechanical strength of the gels, through detailed rheological experiments, indicate that gels from the 1,2-dibenzoylated arabinose gelator possess better mechanical properties than those from the 1,2-diacetylated gelator. These results are interpreted in terms of the tendency of the former to form fibers with comparatively lower diameter than those of the latter, based on detailed field-emission SEM and AFM studies. Investigations of the interactions responsible for the self-assembly of gelators through IR spectroscopy and wide-angle X-ray scattering reveal that the primary interactions responsible are hydrogen bonds between the hydroxyl groups and ester C=O, which is absent in the solid state of the gelators. In addition, π interactions present in the 1,2-dibenzoylated derivative result in a more regular arrangement, which, in turn, leads to better mechanical properties of the gels compared with those of the 1,2-diacetylated gelator.

Probing Gelation and Rheological Behavior of a Self-Assembled Molecular Gel.

Molecular gels have been investigated over the last few decades; however, mechanical behavior of these self-assembled gels is not well understood, particularly how these materials fail at large strain. Here, we report the gelation and rheological behavior of a molecular gel formed by self-assembly of a low molecular weight gelator (LMWG), di-Fmoc-l-lysine, in 1-propanol/water mixture. Gels were prepared by solvent-triggered technique, and gelation was tracked using Fourier transform infrared (FTIR) spectroscopy and shear rheology. FTIR spectroscopy captures the formation of hydrogen bonding between the gelator molecules, and the change in IR spectra during the gelation process correlates with the gelation kinetics results captured by rheology. Self-assembly of gelator molecules leads to a fiber-like structure, and these long fibers topologically interact to form a gel-like material. Stretched-exponential function can capture the stress-relaxation data. Stress-relaxation time for these gels have been found to be long owing to long fiber dimensions, and the stretching exponent value of 1/3 indicates polydispersity in fiber dimensions. Cavitation rheology captures fracture-like behavior of these gels, and critical energy release rate has been estimated to be of the order 0.1 J/m2. Our results provide new understanding of the rheological behavior of molecular gels and their structural origin.

Photochromic property of naphthalimide derivative: Selective and visual F− recognition by NSS isomers both in solution and in a self-assembly gel

A novel fluorescent organogelator NSS comprised of CN and NNH units was designed and characterized. By light irradiation, NSS could undergo trans to cis transformation both in solution and gel state, which was accompanied by dramatic color, fluorescence intensity, and emission color changes, indicating the photochromic property of NSS. Both of the gels in E-isomeric and Z-isomeric forms could selectively response to fluoride anion among tested anions. Further study presented that the two isomers displayed different signal outputs and binding mechanisms toward fluoride anion. Especially, the organogel of NSS in the E-isomeric form showed selective, visual, and reversible sensing for fluoride anion. Beside the above functions, the organogel could also response to ultrasound and heating stimuli, thus endowing the organogel with multi-stimuli responsive properties.

Design, synthesis, and characterisation of glyoxylamide-based short peptides as self-assembled gels

First example of glyoxylamide-based short peptides which can encapsulate organic solvents and water at relatively low concentrations.

Gelation of soybean protein and polysaccharides delays digestion.

Xanthan gum and carrageenan, representing the medium and highly negatively charged polysaccharides, were heated respectively together with soybean protein isolate (SPI) at different biopolymer ratios. Upon mixing with simulated stomach juice (SSJ), the xanthan-SPI and carrageenan-SPI at biopolymer ratios higher than 0.01 leads to self-assembled gelation immediately. Stronger gel is formed under higher biopolymer ratios. Highly negatively charged carrageenan forms a stronger gel than that composed with xanthan gum. SDS-PAGE results show the digestibility of SPI is delayed after incorporation with the polysaccharides, which is enhanced with the increase of the biopolymer mass ratios. And the polysaccharide with higher negative charge has stronger potential in delaying the digestion of SPI. Furthermore, the microstructure of the xanthan-SPI and carrageenan-SPI gel before and after simulated stomach digestion was characterized by scanning electron microscope (SEM), which also confirms that the gel delays the digestion of soybean protein.

A Facile Method for Synthesizing Dendritic Core–Shell Structured Ternary Metallic Aerogels and Their Enhanced Electrochemical Performances

Currently, three-dimensional self-supported metallic structures are attractive for their unique properties of high porosity, low density, excellent conductivity, etc., that promote their wide application in fuel cells. Here, for the first time, we report a facile synthesis of Au@Pt3Pd ternary metallic aerogels with a unique dendritic core–shell structure via a one-pot self-assembly gelation strategy. This strategy is simple and saves time without any concentration or destabilizer steps. The as-prepared Au@Pt3Pd ternary metallic aerogels demonstrated enhanced electrochemical performance toward the oxygen reduction reaction compared to that of commercial Pt/C. The unique dendritic core–shell structures, Pt3Pd alloyed shells, and cross-linked network structures are beneficial for the electrochemical oxygen reduction reaction via the electronic effect, geometric effect, and synergistic effect. This strategy of fabrication of metallic hydrogels and aerogels as well as their exceptional properties holds great p...

On-Demand Drug Delivery System Using Micro-organogels with Gold Nanorods.

In this study, we designed a biocompatible drug carrier: micro-organogels prepared by emulsification using vegetable oils and self-assembled gelator fibers. Flurbiprofen was chosen as a hydrophobic model drug and is classified as a nonsteroidal anti-inflammatory drug. In the absence of NIR light, flurbiprofen encapsulated in micro-organogels with gold nanorods (GNRs) was released slowly, while release was accelerated in the presence of NIR light due to the increase in the temperature surrounding the GNRs that transforms the gels into liquid. These results suggest that our system can be efficiently used as a versatile scaffold for on-demand drug delivery systems.

Effect of the self-assembled gel network formed from a low molecular mass organogelator on the electron kinetics in quasi-solid-state dye-sensitized solar cells

A low molecular mass organogelator (LMOG), N , N ¢ -1,5-pentanediylbis-dodecanamide, was applied to quasi-solid-state dye-sensitized solar cells (QS-DSSCs). The crosslinked gel network was self-assemblied by the LOMG in the liquid electrolyte, and the in situ assembly process of gelator can be obtained by the polarized optical microscopy (POM). On one hand, the network hinders the diffusion of redox species and accelerates the electron recombination at the interface of the TiO2 photoanode/electrolyte. On the other hand, Li+ can interact with the amide carbonyl groups of the gelators and the adsorption of Li+ onto the TiO2 surface decreases, leading to a negative shift of the TiO2 conduction band edge, accelerated electron transport and decreased electron injection efficiency ( η inj) of QS-DSSC. As a result, the incidental photon-to-electron conversion efficiency (IPCE), the short circuit photocurrent density ( J sc) and the open circuit voltage ( V oc) of the QS-DSSC are decreased compared with those of the liquid electrolyte based DSSC (L-DSSC), which indicates that the electron recombination plays a great role in the photovoltaic performances of DSSC. Remarkably, the QS-DSSC exhibits excellent thermal and light-soaking stabilities during accelerated aging tests for 1000 h, which is attributed to a great intrinsic stability of the gel electrolyte with a high gel to solution transition temperature ( T gel = 108°C).

Proportion of marine organic carbon present in self-assembled gels along the subtropical front and its increase in response to reduced pH

Dissolved organic matter (DOM), the largest marine reservoir of reduced carbon, which contains a complex mix of polydisperse biopolymers and particularly small molecules in solution. However, we now know that about 10% of these dissolved moieties can spontaneously aggregate forming a huge mass of highly bioreactive microscopic particles by forming self-assembled gels (SAG) with a significant role in global carbon cycling. However, the effect of varying marine environments on DOM self-assembly remains virtually unknown. Here we report variations of the fraction of DOM that self-assemble forming gels (%SAG) measured in seawater samples collected during two different periods — before and during the autumn bloom— along the Subtropical Frontal Zone off New Zealand; an area characterized by strong spatiotemporal physicochemical and biological variability. Results show that %SAG varies in time and space. Measurements of %SAG ranged between 9–28% (14.5±5, mean±SD), and this broad variability could be partly associated to changes in phytoplankton biomass and/or UV radiation. Additional studies on the effect of a pH on the %SAG, reveal that small pH reductions of 0.3units can virtually double the %SAG from 14.5±5 to 27±7% (12.5±4%, mean±SD). The observed increase in the %SAG under reduced pH was observed in all samples, irrespectively of their origin. This outcome suggests that pH might be a critical parameter controlling the formation of gels in marine environments. Decreased pH increases the SW concentration of free ionized Ca ([Ca+2]), the prime DOM crosslinker. Rising [Ca+2] is likely responsible for the observed %SAG increase. The outcome that %SAG can be strongly affected by small changes in seawater properties, suggest that DOM self-assembly is remarkably responsive to subtle variations of environmental conditions. SAG are a leading source of bacterial nutrition and these observations have potentially strong ramifications in the ecology and biogeochemical cycles of the oceans.

Fabrication of resonance core assisted self-assembling gelators derived from cyclohexanone

Three high-resonance core compounds, BHC-6, BHC-11 and BHC-cho, were synthesized. The morphologies of the self-assembled xerogels of the synthesized compounds were studied using SEM and TEM. The molecular interactions and the formation of asymmetric constructions were investigated using temperature-dependent 1H NMR spectroscopy and circular dichroism spectrometry, respectively. The induction of an asymmetric helical structure was further confirmed using TEM. The results show that increasing the resonance length strengthens intermolecular forces, leading to the formation of gels. A chiral environment produces a steric field effect, leading to the formation of asymmetric constructions. The interactions between functional groups were further confirmed using 2D nuclear overhauser effect spectroscopy NMR. The reversible E–Z isomerization and dimer formation of cinnamoyl derivatives were investigated using UV–vis and fluorescence spectrometry, relatively.

Self-assembled drug delivery system based on low-molecular-weight bis-amide organogelator: synthesis, properties and in vivo evaluation

Context: Orgnaogels based on amino acid derivatives have been widely used in the area of drug delivery.Objective: An organogel system based on l-lysine derivatives was designed and prepared to induce a thermal sensitive implant with higher transition temperature, better mechanical strength, and shorter gelation time.Materials and methods: The organogel was prepared by injectable soybean oil and methyl (S)-2,5-ditetradecanamidopentanoate (MDP), which was synthesized for the first time. Candesartan cilexetil (CC) was chosen as model drug. Different formulations were designed and optimized by response surface method. Thermal, rheology properties, and gelation kinetics of the optimized formulation had been characterized. The release behaviors in vitro, as well as in vivo were evaluated in comparison with the oily solution of drugs. Finally, the local inflammation response of in situ organogel was assessed by histological analysis.Results and discussion: Results showed that the synthesized gelator, MDP, had a good gelation ability and the organogels obtained via the self-assembly of gelators in vegetable oils exhibited great thermal and rheology properties, which guaranteed their state in body. In vivo pharmacokinetic demonstrated that the organogel formulation could extend the drug release and maintain a therapeutically effective plasma concentration at least 10 d. In addition, this implant showed acceptable moderate inflammation.Conclusion: The in situ forming l-lysine-derivative-based organogel could be a promising matrix for sustained drug delivery of the drugs with low solubility.