Fibrillar Gels Research Articles

Enhanced stabilization of oil-in-water (O/W) emulsions by fibrillar gel particles from lentil proteins

Pulse proteins as a sustainable protein source have attracted increasing interest in food development, but pulse proteins are generally less surface active than dairy proteins. This work introduces lentil protein (LP)-based fibrillar gel particles (FGPs) fabricated from heat-induced LP fibrillar aggregates by 1, 4, 8, and 16 h of heating, followed by particle reduction using sonication. The heating time significantly impacts the FGPs particle size and surface hydrophobicity. The FGP prepared by 4 h of heating (FGP-4) showed a small size (<200 nm) and homogeneous size distribution while possessing significantly increased surface hydrophobicity compared to untreated LP. Such structural features made FGP-4 better adsorb at the O/W interface and then completely covered the oil droplet surface, leading to homogeneous emulsions of small size (22.33 μm) and superior long-term stability without creaming for 30 days. In addition, the dispersed FGP in the bulk phase could develop interactions among each other, leading to improved emulsion viscosity and texture without oil droplet size change. This finding suggests that constructing fibril-type gel particles can provide a new strategy for forming superior O/W emulsions with improved stability from plant proteins.

Heat-set supramolecular polymer gel and decomposition by guests

A degradable, heat-set fibrillar gel by supramolecular polymer in DMF based on stearic acid appended l-lysine, β-cyclodextrin and potassium carbonate has been developed. The heat-set stable, irreversible gel decomposed by aromatic guest molecules.

Role of chlorogenic acid and procyanidin in the modification of self-assembled fibrillar gel prepared from tilapia collagen

Collagen fibrillar gels (CFG), formed by self-assembly, displayed similar structure and properties to native tissues. Plant polyphenols showed antioxidant and antibacterial capacity, etc. Previous reports stated introduction of polyphenols could improve the properties of collagen-based material. However, only a few studies were reported on the modification of CFG by polyphenols. In the study, tilapia CFG was cross-linked with chlorogenic acid (CGA) and procyanidin (PC), respectively. The cross-linking conditions were investigated. Results showed PC endowed CFG with higher cross-linking effect at saturation than CGA. ATR-FTIR and XPS displayed there were stronger hydrogen bonds between -OH groups of PC and C = O groups of CFG, but weaker in CGA, confirmed by molecular docking simulation. XRD and SEM indicated PC induced the denser network formed by thinner fibrils, not present in CGA. As a result, water absorption and retention capacity, mechanical properties and enzymatic resistance of gel were improved evidently, whereas thermal stability reduced. Additionally, polyphenol cross-linking granted better antioxidant activity to gel, PC resulting in higher DPPH and PTIO radical scavenging ratio, while CGA showing higher Fe(II) chelation ratio. It also induced better antibacterial activity against Staphylococcus aureus, especially PC cross-linking. The results revealed CFG cross-linked by PC showed better properties compared with CGA, making it have potential application in biomaterials.

Behavior of colloidal gels made of thermoresponsive anisotropic nanoparticles

Amongst colloidal gels, those designed by the assembly of anisotropic colloidal particles tend to form fibrillar gels and are attracting interest as artificial cell growth environments since they have a structure reminiscent of biological extracellular matrices. Their properties can be tuned by controlling the size, shape, and rigidity of the nanoparticles used during their formation. Herein, the relationship between the physical and mechanical properties of the nanocolloidal building blocks and the properties of the resulting gels is investigated. Thermoresponsive particles with different aspect ratios and controlled rigidity were prepared, and the gelation and the properties of the resulting gels were studied. The results show how the aspect ratio and rigidity of polymer colloids tune the properties of the gels. An increase in the aspect ratio of the nanocolloid used led to a sol–gel transition observed at lower particle concentration, but an increase in the rigidity of the nanocolloids delayed the sol–gel transition to higher concentration. However, at a constant concentration, increases in the anisotropy produced gels with higher modulus and lower yield strain. Similarly, an increase in rigidity of the colloids increased the modulus and reduced the yield strain of the resulting gels.

A comparative study on cross-linking of fibrillar gel prepared by tilapia collagen and hyaluronic acid with EDC/NHS and genipin

Chemical cross-linking is an important step to grant satisfying properties to collagen-based materials. However, there are few comparative studies on crossing-linking of collagen-based fibrillar gels which are preferred biomaterials for similar properties to native tissues with different cross-linking agents. In this study, a fibrillar gel was fabricated with tilapia collagen and hyaluronic acid, and cross-linking conditions with EDC/NHS and genipin were discussed. Genipin gave gels much higher equilibrium cross-linking degree than EDC/NHS. ATR-FTIR and XPS showed EDC/NHS offered short-range cross-linking formed by amino and carboxyl groups in fibrils, while genipin induced long-range cross-linking by nucleophilic reaction through attack of amino groups in fibrils on carbon atoms at C-3 as well as ester groups in genipin, besides improved hydrogen bonds. XRD and SEM revealed the structural integrity of gels was strengthened after cross-linking, whereas fibril bundles disaggregated into thin fibrils. Consequently, swelling capacity and anti-degraded property were enhanced significantly, while thermal stability weakened. The fibrillar gels had good biocompatibility, but interestingly the appearance and migration of L929 fibroblasts were influenced by cross-linking degree. These results demonstrated that aquatic collagen-based fibrillar gel cross-linked by genipin had greater potential in biomaterials than EDC/NHS, whereas the cross-linking degree should be controlled.

Effects of cross‐linking with EDC/NHS and genipin on characterizations of self‐assembled fibrillar gel prepared from tilapia collagen and alginate

Chemical cross-linking is prevalent for precise control of the properties of collagen-based materials. However, there is little information about detailed comparisons of cross-linking characteristics of collagen-based fibrillar gel with different cross-linkers. In this study, a fibrillar gel was prepared from tilapia collagen and alginate, and cross-linking conditions with EDC/NHS and genipin were discussed. By curve-fitting with Langmuir and pseudo-second-order model, the cross-linking process was controlled by monolayer chemisorption, and genipin showed much higher cross-linking degree at saturation compared with EDC/NHS. ATR-FTIR and XPS suggested that although hydrogen bonds were weakened by cross-linking, EDC/NHS offered short-range cross-linking formed by amino and carboxyl groups in fibrils, while genipin induced long-range cross-linking by interactions of amino groups in fibrils and ester groups in genipin. XRD and SEM revealed that the structural integrity was strengthened after cross-linking, however, fibril bundles were present in SA/PSC/EDC/NHS, and genipin induced disaggregation of fibrils. Both swelling properties and enzymatic resistance were improved by cross-linking, while thermal stability was unenhanced significantly. All fibrillar gels showed good biocompatibility, but cross-linking degree affected appearance and migration of cells. The results revealed that genipin-cross-linked fibrillar gel had greater potential application in biomaterials on the premise of tuning cross-linking degree than EDC/NHS-cross-linked one.

Building a supramolecular gel with an ultra-low-molecular-weight Schiff base gelator and its multiple-stimulus responsive properties

An unprecedented Schiff base gelator with ultra-low molecular weight (Mw=188) was facilely prepared from readily available starting materials in a single step. The gelator was found to possess a strong gelation ability with the critical gelation concentration down to 0.45 wt% in dichloromethane (DCM). FT-IR NMR, XRD, SEM, theoretical calculation, and control experiment were combined to elucidate the assembly mechanism of gelator leading to gel. It was revealed that the hydrogen bonding associated with the triazole NH moiety plays a crucial role in the formation of the fibrillar gel network. This supramolecular gel demonstrated multiple-stimulus responsive (temperature, pH, metal ion) gel-sol phase transition behavior, particularly interesting aspect is that only 0.13 eq. F- is required to collapse the gel, representing the most sensitive supramolecular gel to F- anion up to now and endowing it with great potential as F- detector. The newly found Schiff base gelator reported here would offer prospects for the future design of more intelligent materials based on simple but versatile molecular scaffolds.

Fibrillar gel self-assembly via cononsolvency of amphiphilic polymer

HypothesisPolymer with amphiphilic repeating units bathed in the mixed binary solvent can exhibit fibrillar formation and gelation via cononsolvency effect. Mechanism of gelation will be highly dependent on the solvent’s interactions and morphology of the resulting fibrillar gel can be fine-tuned by changing binary solvent composition. ExperimentsAmphiphilic homopolymers dissolved in a mixture of two solvents with different affinities to monomeric units and to each other were modeled using dissipative particle dynamics. Morphological transitions in dilute and concentrated solutions were investigated depending on the solvent-cosolvent interaction and binary solvent composition. Fibrillar gel structure was characterized via calculation of fibril’s and pore’s diameters. FindingsAmphiphilic macromolecules can combine into fibrils and form a gel as a result of the cononsolvency caused by microsegregation with one or both components of a binary solvent. In the former, the fibrils are loose, in the latter - dense. For dilute solution, state diagram in terms of solvent/cosolvent miscibility and binary solvent composition is constructed and two regions with different fibrillar gels are distinguished. For concentrated solution, the conditions, governing fibrillar diameter, pore size, number and functionality of branching points, are highlighted. These findings would be useful for the controlling synthetic matrix morphologies in the tissue engineering.

Fibril Assembly and Gelation of Macromolecules with Amphiphilic Repeating Units.

This paper reports the self-assembly of the fibrillar network in a concentrated solution of macromolecules with an amphiphilic structure of repeating units. The investigation of amphiphilic homopolymers and alternating copolymers with the linear and cyclic topologies, the solution with different polymer concentrations and solvent qualities, allows us to conclude that the ability to form a fibrillar gel with branched fibrils and regular subchain thickness is inherent for macromolecules with the solvophobic backbone and solvophilic pendants. The elements of the gel structure, such as the mesh size and fibrillar thickness, the number of cross-links, and their functionality, can be tuned and customized according to the requirements of their application. The results could be helpful for the directed design of the synthetic analogue of the relevant extracellular matrix, in tissue engineering, for fibrotic disease treatment and cell encapsulation.

Magnetic Assembly of a Multifunctional Guidance Conduit for Peripheral Nerve Repair

AbstractNerve growth conduits are designed to support and promote axon regeneration following nerve injuries. Multifunctionalized conduits with combined physical and chemical cues, are a promising avenue aimed at overcoming current therapeutic barriers. However, the efficacious assembly of conduits that promote neuronal growth remains a challenge. Here, a biomimetic regenerative gel is developed, that integrates physical and chemical cues in a biocompatible “one pot reaction” strategy. The collagen gel is enriched with magnetic nanoparticles coated with nerve growth factor (NGF). Then, through a remote magnetic actuation, highly aligned fibrillar gel structure embedded with anisotropically distributed coated nanoparticles, combining multiple regenerating strategies, is obtained. The effects of the multifunctional gels are examined in vitro, and in vivo in a 10‐mm rat sciatic nerve injury model. The magneto‐based therapeutic conduits demonstrate oriented and directed axonal growth, and improve nerve regeneration in vivo. The study of multifunctional guidance scaffolds that can be implemented efficiently and remotely provides the foundation to a novel therapeutic approach to overcome current medical obstacles for nerve injuries.

Heat-induced gel formation by whey protein isolate-Lycium barbarum polysaccharides at varying pHs

Effects of different levels (0, 0.1, 0.5, and 1% w/v) of Lycium barbarum polysaccharides (LBP) were investigated on the gel properties of heat-induced whey protein gels forming at varying pHs (3.0, 5.2 and 7.0). The textural, rheological, hydration properties and microstructure of gels were evaluated. Results exhibited that the composite gel containing 0.1% (w/v) LBP showed the greatest functional valorization, whereas higher concentrations of LBP (1% w/v) yielded hydrogels with higher porosity, which was confirmed by scanning electron microscopy. Moreover, whey protein formed white particulate gels and transparent fibrillar gels at pH values near to and far from the isoelectric point, respectively. As for hydration properties, no difference in water holding capacity and swelling property was observed at all pHs. This study simulated the conditions used in practical production, aiming to provide a theoretical basis for the application of LBP on composite gels and develop tunable gel-type food to satisfy different consumer preferences.

Preparation of self-assembled collagen fibrillar gel from tilapia skin and its formation in presence of acidic polysaccharides

Fibrillar gel of pepsin-solubilized collagen from tilapia skin was prepared by self-assembly in neutral phosphate buffer at 28 °C. Then effects of acidic polysaccharides, such as sodium alginate (SA), chondroitin sulfate (CS), and hyaluronic acid (HA), on the formation and properties of self-assembled fibrillar gel were investigated. SA and CS prolonged gelling time, whereas HA had no obvious effect. SA made fibril network denser, while CS and HA induced the presence of larger ordered structures. All the acidic polysaccharides broadened the D-periodicity of fibrils. SA and HA increased the maximum mechanical strength of gel to 39.64 and 34.49 kN/m2, respectively, significantly higher than that of pure collagen gel (14.53 kN/m2), while that only 17.20 kN/m2 after CS introduced. HA had no evident effect on enzymatic resistance, while SA and CS decreased. Therefore, tilapia skin collagen with HA has a higher potential as a biomaterial than that with CS or SA.

Hierarchical microfibrillar gels from evaporation-induced anisotropic self-assembly of in situ-generated nanocrystals

Whilst nanocrystal gels may be formed via destabilization of pre-functionalized nanocrystal dispersions, gelation via assembly of unfunctionalized nanocrystals into fibrillar networks remains a significant challenge. Here, we show that gels with hierarchical microfibrillar networks are formed from anisotropic self-assembly of in situ-generated mesolamellar nanocrystals upon evaporation of ZnO nanofluids. The obtained gels display the thermo-reversible behavior characteristic of a non-covalent physical gel. We elucidate a three-stage gelation mechanism. In the pre-nucleation stage, the cloudy ZnO nanofluid transforms into a transparent stable suspension, comprising multi-branched networks of aggregates self-assembled from in situ-generated layered zinc hydroxide (LZH) nanocrystals upon solvent evaporation. In the subsequent nucleation and anisotropic 1D fibre growth stage, further evaporation triggers nucleation and growth of 1D nanofibers through reorganization of the nanocrystal aggregates, before rapid nanofibre bundling leading to microfibrillar networks in the ultimate gelation stage. Our results provide mechanistic insights for hierarchical self-assembly of nanocrystals into fibrillar gels and open up facile fabrication routes using reactive transition metal-oxide nanofluids for new functional fibres and gels.

Composite Gels Containing Whey Protein Fibrils and Bacterial Cellulose Microfibrils.

In this study, we investigated the gelation of WPI fibrils in the presence of bacterial cellulose (BC) microfibrils at pH 2 upon prolonged heating. Rheology and microstructure were investigated as a function of BC microfibril concentration. The presence of BC microfibrils did not influence the gelation dynamics and resulting overall structure of the WPI fibrillar gel. The storage modulus and loss modulus of the mixed WPI‐BC microfibril gels increased with increasing BC microfibril concentration, whereas the ratio between loss modulus and storage modulus remained constant. The WPI fibrils and BC microfibrils independently form two coexisting gel networks. Interestingly, near to the BC microfibrils more aligned WPI fibrils seemed to be formed, with individual WPI fibrils clearly distinguishable. The level of alignment of the WPI fibrils seemed to be dependent on the distance between BC microfibrils and WPI fibrils. This also is in line with our observation that with more BC microfibrils present, WPI fibrils are more aligned than in a WPI fibrillar gel without BC microfibrils. The large deformation response of the gels at different BC microfibril concentration and NaCl concentration is mainly influenced by the concentration of NaCl, which affects the WPI fibrillar gel structures, changing form linear fibrillar to a particulate gel. The WPI fibrillar gel yields the dominant contribution to the gel strength.

The Kinetics, Thermodynamics and Mechanisms of Short Aromatic Peptide Self-Assembly.

The self-assembly of short aromatic peptides and peptide derivatives into a variety of different nano- and microstructures (fibrillar gels, crystals, spheres, plates) is a promising route toward the creation of bio-compatible materials with often unexpected and useful properties. Furthermore, such simple self-assembling systems have been proposed as model systems for the self-assembly of longer peptides, a process that can be linked to biological function and malfunction. Much effort has been made in the last 15 years to explore the space of peptide sequences, chemical modifications and solvent conditions in order to maximise the diversity of assembly morphologies and properties. However, quantitative studies of the corresponding mechanisms of, and driving forces for, peptide self-assembly have remained relatively scarce until recently. In this chapter we review the current state of understanding of the thermodynamic driving forces and self-assembly mechanisms of short aromatic peptides into supramolecular structures. We will focus on experimental studies of the assembly process and our perspective will be centered around diphenylalanine (FF), a key motif of the amyloid β sequence and a paradigmatic self-assembly building block. Our main focus is the basic physical chemistry and key structural aspects of such systems, and we will also compare the mechanism of dipeptide aggregation with that of longer peptide sequences into amyloid fibrils, with discussion on how these mechanisms may be revealed through detailed analysis of growth kinetics, thermodynamics and other fundamental properties of the aggregation process.

Air-Sensitive Photoredox Catalysis Performed under Aerobic Conditions in Gel Networks.

In this work, we demonstrate that useful C-C bond-forming photoredox catalysis can be performed in air using easily prepared gel networks as reaction media to give similar results as are obtained under inert atmosphere conditions. These reactions are completely inhibited in homogeneous solution in air. However, the supramolecular fibrillar gel networks confine the reactants and block oxygen diffusion, allowing air-sensitive catalytic activity under ambient conditions. We investigate the mechanism of this remarkable protection, focusing on the boundary effect in the self-assembled supramolecular gels that enhances the rates of productive reactions over diffusion-controlled quenching of excited states. Our observations suggest the occurrence of triplet-sensitized chemical reactions in the gel networks within the compartmentalized solvent pools held between the nanofibers. The combination of enhanced viscosity and added interfaces in supramolecular gel media seems to be a key factor in facilitating the reactions under aerobic conditions.

A dual pH-responsive supramolecular gelator with aggregation-induced emission properties.

Functionalising AIE-active aromatic thioethers with self-complementary zwitterionic binding sites leads to a dual pH-responsive supramolecular organogelator with aggregation-induced emission (AIE) properties. The self-assembled fibrillar gel network is highly fluorescent (λem = 490 nm), whereas the addition of both acid and base leads to the sol state with a loss of emission. More over, the gel was found to be thermo- and mechanoresponsive.

Characterization of three-spot seahorse (Hippocampus trimaculatus ) skin collagen and its fibrillar gel reinforced by EDC: A comparative study

In current study, three-spot seahorse (Hippocampus trimaculatus) skin collagen (SC) was extracted for the first time, and its physicochemical properties were characterized. Nile tilapia-skin collagen (TC) and pig-skin collagen (PC) were used to the references. The yields of SC and TC were 40.41 ± 1.23 and 52.6 ± 0.97% (dry weight), respectively. The SDS-PAGE and FTIR confirmed that SC, TC, and PC were preliminarily identified as type I collagen with triple helical structure. The denaturation temperatures of SC, TC, and PC were 35.12, 38.66, and 42.56°C, respectively. Gel-forming studies indicated SC exhibited higher capability than TC and PC under the effect of NaCl. After cross-linking by 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC), SC showed a significant increase in thermal stability and mechanical strength, and electron microscopic observation corroborated this phenomenon. Therefore, the isolated collagen from three-spot seahorse skin can be used in food packaging and biomaterials as alternatives to mammalian collagen. Practical applications In this study, we evaluated a new source of skin collagen from three-spot seahorse which has been large-scale artificially cultured in recent years. The finding of this study demonstrate that SC exhibited higher gel-forming capability under the effect of NaCl, which suggest that it may be used in photographic film, sausage casings, and food additive as alternatives to mammalian collagen. Furthermore, thermal stability and mechanical strength of SC gel have a significant increase after cross-linking by EDC, so it can be further used for biomaterials, such as food packaging, drug delivery, tissue engineering constructs, and wound dressing systems.

Influence of residual composition on the structure and properties of extracellular matrix derived hydrogels

In this work, hydrolysates of extracellular matrix (hECM) were obtained from rat tail tendon (TR), bovine Achilles tendon (TAB), porcine small intestinal submucosa (SIS) and bovine pericardium (PB), and they were polymerized to generate ECM hydrogels. The composition of hECM was evaluated by quantifying the content of sulphated glycosaminoglycans (sGAG), fibronectin and laminin. The polymerization process, structure, physicochemical properties, in vitro degradation and biocompatibility were studied and related to their composition. The results indicated that the hECM derived from SIS and PB were significantly richer in sGAG, fibronectin and laminin, than those derived from TAB and TR. These differences in hECM composition influenced the polymerization and the structural characteristics of the fibrillar gel network. Consequently, the swelling, mechanics and degradation of the hydrogels showed a direct relationship with the remaining composition. Moreover, the cytocompatibility and the secretion of transforming growth factor beta-1 (TGF-β1) by macrophages were enhanced in hydrogels with the highest residual content of ECM biomolecules. The results of this work evidenced the role of the ECM molecules remaining after both decellularization and hydrolysis steps to produce tissue derived hydrogels with structure and properties tailored to enhance their performance in tissue engineering and regenerative medicine applications.

TiO2 Nanoparticles Incorporated Peptide Appended Perylene Bisimide-Based Nanohybrid System: Enhancement of Photo-Switching Behavior

A peptide appended perylene bisimide (PBI)-based new hydrogel has been discovered in phosphate buffer medium having the pH ranging from 7.00 to 9.00. This peptide appended PBI-derivative shows interesting photoswitching property in the aggregated state. This gel is thoroughly characterized by UV–visible absorption and fluorescence spectroscopy, field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), and rheological studies. TiO2 nanoparticles are also prepared by using a protein amino acid, glutamic acid, in water medium. The as-synthesized TiO2 nanoparticles exhibit usual photoswitching behavior. An organic–inorganic hybrid nanomaterial is prepared by incorporating the as-synthesized TiO2 nanoparticles into the fibrillar gel network of the native gel. This TiO2–PBI-based hybrid soft material shows a characteristic of nanofiber and nanoparticle combination in their nanoscale coassembled state as it is evident from the respec...