Gel-like Properties Research Articles

Gel‐like inclusions of C‐terminal fragments of TDP‐43 sequester stalled proteasomes in neurons

Aggregation of the multifunctional RNA‐binding protein TDP‐43 defines large subgroups of amyotrophic lateral sclerosis and frontotemporal dementia and correlates with neurodegeneration in both diseases. In disease, characteristic C‐terminal fragments of ~25 kDa ("TDP‐25") accumulate in cytoplasmic inclusions. Here, we analyze gain‐of‐function mechanisms of TDP‐25 combining cryo‐electron tomography, proteomics, and functional assays. In neurons, cytoplasmic TDP‐25 inclusions are amorphous, and photobleaching experiments reveal gel‐like biophysical properties that are less dynamic than nuclear TDP‐43. Compared with full‐length TDP‐43, the TDP‐25 interactome is depleted of low‐complexity domain proteins. TDP‐25 inclusions are enriched in 26S proteasomes adopting exclusively substrate‐processing conformations, suggesting that inclusions sequester proteasomes, which are largely stalled and no longer undergo the cyclic conformational changes required for proteolytic activity. Reporter assays confirm that TDP‐25 impairs proteostasis, and this inhibitory function is enhanced by ALS‐causing TDP‐43 mutations. These findings support a patho‐physiological relevance of proteasome dysfunction in ALS/FTD.

Pickering emulsions stabilized with chitosan/gum Arabic particles: Effect of chitosan degree of deacetylation on the physicochemical properties and cannabidiol (CBD) topical delivery

Pickering emulsions (PEs) have recently gained increasing attention as green carriers of bioactive agents due to their surfactant-free and eco-friendly nature. Herein, the effect of the degree of deacetylation (DDA) of chitosan on the properties of chitosan/gum Arabic (CH/GA) particles and PEs was investigated. CH/GA particles with a DDA of 96% (high DDA) and 78% (low DDA) were prepared. The contact angle of water drop for the CH/GA particles prepared with high and low DDA chitosan was 84.2° and 77.5°, respectively. The dynamic interfacial tension of the particles has shown lower values with high DDA chitosan. The high DDA PE formulation exhibited higher stability after two months of storage than its counterpart prepared with low DDA chitosan. The mean emulsion droplet size was 15.6 ± 4.3 µm and 21.1 ± 2.6 µm for PEs prepared with high and low DDA chitosan, respectively. Both PE formulations demonstrated shear thinning and elastic gel-like properties. The amount of cannabidiol absorbed by the stratum corneum, viable epidermis and dermis was significantly higher in both PE formulations than the permeated amount, but no significant difference was observed between the amounts absorbed from both formulations.

Rheological elucidation of the viscoelastic properties and network interaction of mixed high-methoxyl pectin and kappa-carrageenan gels

The interaction between two anionic polysaccharides known for their gelation capability was investigated. Mixtures of high-methoxyl pectin (HMP) and κ-carrageenan (KC) were prepared at different volume fractions. The sample's complex rheological properties and microstructures were investigated by performing linear small amplitude oscillatory shear (SAOS) and nonlinear large amplitude oscillatory shear (LAOS). Pure KC and the HMP/KC mixtures exhibited gel-like properties, whereas pure HMP did not gel at the experimental conditions employed and was characterized as a viscoelastic liquid. Temperature-dependent rheological behavior of HMP/KC mixtures suggested the independent aggregation of KC chains. The viscoelastic properties of the HMP/KC mixtures, such as oscillatory spectrum, and material stiffness, followed that of pure KC, indicating that KC strongly influenced the final gel. The transient behavior of the HMP/KC mixtures in the time sweep and the monotonic decrease of the storage modulus in the linear regime, and the onset of nonlinear rheological behavior in the strain sweep measurements suggested the possibility of the phase-separated network structure of in HMP-rich and KC-rich phases in the mixtures. Based on the rheological data both in the linear and nonlinear regimes, we propose the possibility of a bicontinuous network structure in HMP/KC mixtures, composed of the weak HMP phase in random coil configuration and the dominant KC phase in double helix aggregates.

Rheological Characterization of Sulfuric Acid Solutions of Poly(p-phenyleneterephthalamide)

Abstract Several grades of poly(p-phenyleneterephthalamide) (PPD-T) with different molecular weights were prepared. The rheological properties of sulfuric acid solutions of PPD-T were measured. In the vicinity of the critical concentration tan <5 and η'/G' exhibited a minimum value, but G'/2G" and η* showed a maximum value. High concentrations produce an anisotropic phase. Tendencies of yield behavior were observed for these solutions in the anisotropic phase. Above the saturated concentration the solution system showed gel-like properties, i. e., with increasing concentration abrupt reduction of G'/2G” and abrupt increases of η*, η'/G' and tan δ were observed. With increasing temperature the viscosity of isotropic and anisotropic phases was decreased but that of biphase was increased. The critical concentration was reduced with increasing molecular weight, but increased with increasing temperature. Use of reduced variables seemed to eliminate molecular weight dependency on the critical concentration curve. The shear viscosity appeared to be proportional to (Mw)6,7.

A hairpin to duplex conversion underlies RNA foci phase transitions

RNA foci, liquid-liquid phase separated droplets composed of repeat expansion RNAs, are a common clinical feature of neurodegenerative disorders including myotonic dystrophy, Huntington's disease, and amyotrophic lateral sclerosis. It has recently been demonstrated that trinucleotide repeat RNAs spontaneously undergo phase separation in a sequence, length, and base-pairing dependent process and exhibit liquid-like or gel-like properties in vivo and in vitro, respectively. The role of RNA foci in neurodegeneration is still unclear, but these results suggest there is a dynamic RNA process that is disturbed by repeat expansion mutations.

Structure and rheological studies of phosphorylated cellulose nanofibrils suspensions

Cellulose nanofibrils (CNFs) are normally handled in the form of aqueous suspensions. Therefore, their rheology and intrinsic flow features in an aqueous state also fascinated the researchers. However, understanding the structure-rheology relationship remains a profound challenge to design CNFs with desirable properties. For that purpose, jute fibers were used as source material (Corchorus olitorius) to produce CNFs, and pretreatment using phosphorylation was applied to facilitate the fibrillation during ultra-sonication. This study aims to investigate the relationship between the microstructure and their rheology for CNF aqueous suspensions as influenced by the temperature and concentration of CNF. The surface chemistry, fiber diameter distribution, crystalline structure, thermal stability, and rheological properties of the obtained CNFs were characterized and compared. The grafting of phosphorous moieties on the surface of the fibers was confirmed by the FTIR, XPS analyses, elemental analyses, and zeta potential. Despite influencing crystallinity, phosphorylation enhanced the diameter of nanofibers. The results demonstrated that phosphorylation did not alter the main chemical structure of cellulose. The crystallographic form of the obtained CNFs remained cellulose I. The resulting fibers have nanometric dimensions (<100 nm) with high absolute zeta potential values (>30 mV). A substantial improvement in flame retardancy has also been noted for CNF due to the presence of phosphate groups. Both steady-state and dynamic rheological measurements were improved significantly upon increasing concentration from 0.5 to 2.5 wt%. All the CNF suspensions demonstrated typical shear-thinning behavior and gel-like viscoelastic character even at low concertation (0.5 wt%) due to the construction of a wire-like matrix structure. The frequency and temperature alteration, however, do not affect the viscoelastic gel-like properties of the CNF suspensions.

Functionality of oat fiber concentrate and faba bean protein concentrate in plant-based substitutes for minced meat

Oat has been recognized for its health-promoting fiber, β-glucan, while protein-rich faba bean has remained underutilized in Nordic countries despite its good nutritional quality. This research investigated the functionality of oat fiber concentrate and faba bean protein concentrate in plant-based substitutes for minced meat (SMs). The resulting product aimed at mimicking the mechanical and physicochemical characteristics of beef minced meat (BM) and its applications (i.e., fried and burger patty). In this regard, the mechanical properties (e.g., chewiness, Young's modulus) of original/fried SMs were comparable to or higher than those of original/fried BM. SM patties (45% SMs) were structurally weaker than beef burger patties (100% BM). The rheological analysis showed that the presence of oat fiber concentrate increased the gel-like properties of the blend, which correlated with the overall strength of original SMs (e.g., Young's modulus). The results suggested that SMs could be used as BM for the preparation of vegetarian meat-like products.

Characteristics of Pickering emulsions stabilized by tea water-insoluble protein nanoparticles at different pH values

This study aimed to explore the characteristics of Pickering emulsions stabilized by tea water-insoluble protein nanoparticles (TWIPNs) at different pH values. The characteristics of TWIPNs at different pH values were analysed first. The average hydrodynamic diameter of TWIPNs in the suspension was smaller than 400 nm at pH 7–11. TWIPNs at pH 3 could not be used to stabilize Pickering emulsions. The flocculation index (FI) of fresh TWIPN-stabilized Pickering emulsions (TWIPNPEs) at pH 5 was higher than those of TWIPNPEs at pH 7–11 (FI < 5%), indicating that bridging flocculation led to the aggregation of small emulsion droplets. The zeta potential of TWIPNPEs at pH 7–11 did not change after 7 d. In addition, the TWIPNPEs showed gel-like properties under neutral and alkaline conditions. These results will be helpful for broadening the application of TWIPNPEs at different pH values.

Artificial Extracellular Matrices Containing Bioactive Glass Nanoparticles Promote Osteogenic Differentiation in Human Mesenchymal Stem Cells.

The present study analyzes the capacity of collagen (coll)/sulfated glycosaminoglycan (sGAG)-based surface coatings containing bioactive glass nanoparticles (BGN) in promoting the osteogenic differentiation of human mesenchymal stroma cells (hMSC). Physicochemical characteristics of these coatings and their effects on proliferation and osteogenic differentiation of hMSC were investigated. BGN were stably incorporated into the artificial extracellular matrices (aECM). Oscillatory rheology showed predominantly elastic, gel-like properties of the coatings. The complex viscosity increased depending on the GAG component and was further elevated by adding BGN. BGN-containing aECM showed a release of silicon ions as well as an uptake of calcium ions. hMSC were able to proliferate on coll and coll/sGAG coatings, while cellular growth was delayed on aECM containing BGN. However, a stimulating effect of BGN on ALP activity and calcium deposition was shown. Furthermore, a synergistic effect of sGAG and BGN was found for some donors. Our findings demonstrated the promising potential of aECM and BGN combinations in promoting bone regeneration. Still, future work is required to further optimize the BGN/aECM combination for increasing its combined osteogenic effect.

A Pilot Trial Assessing the Feasibility and Efficacy of a Novel Powder for Rapid Wound Healing

It is well-understood that wound care poses a significant burden on the healthcare system and patient well-being. As such, it is imperative to develop efficient methods that facilitate tissue repair. Our group previously developed a nutritional gel scaffold, proven to accelerate wound repair. Due to its gel-like properties, this scaffold requires a time-consuming reconstitution, and is optimized for cavernous wounds. This pilot study examined the feasibility of a powdered form of this scaffold to accelerate healing of full-thickness wounds, thus broadening the range of applications, while providing a practical product. Splinted full-thickness wounds were generated on the backs of 6 mice, and treated with either powder, the original gel scaffold, or no treatment. Feasibility and efficacy of the powder was assessed through comparison of clinical wound measurements and histological assessments. There was a significant effect of treatment on rate of epithelialization [H(3) = 8.346, p = 0.0024] and on days to epithelial closure [H(3) = 8.482, p = 0.0061]. Post hoc analysis revealed that while requiring no reconstitution and simple to apply, the powder was sufficient to accelerate epithelialization compared to untreated wounds (p &lt; 0.05). Furthermore, our results suggest that application of this powder did not alter certain processes associated with healing progress, such as epidermal thickness and collagen deposition. As such, this powder may provide a novel alternative to our previously developed gel scaffold by accelerating epithelialization, while providing a practical product. Future studies necessitate further evaluation of healing measures with a larger sample size.

Pickering emulsions stabilized with chitosan/collagen peptides nanoparticles as green topical delivery vehicles for cannabidiol (CBD)

Pickering emulsions (PEs) are attracting increasing attention in the areas of food, cosmetic and pharmaceutical applications owing to their surfactant-free and eco-friendly nature. Herein, PEs stabilized by chitosan/collagen peptides (CH/CP) nanoparticles were assessed as green surfactant-free vehicles for the topical delivery of cannabidiol (CBD), a highly lipophilic unstable drug that is finding an increasing appeal in the cosmetic market. The influence of the oil phase volume fraction (φ) and the oil type on the emulsion properties, stability, rheological properties, as well as on the ex-vivo skin absorption of CBD was evaluated. The PE prepared with olive oil (φ = 0.6) exhibited elastic gel-like properties and demonstrated long-term stability after 5 months of storage, with a CBD content of 99.45% of the initially added amount. The skin absorption studies showed that CBD was retained in high amounts in the stratum corneum, while the CBD skin permeation was extremely low, indicating that the produced formulations are suitable as topical delivery vehicles. ATR-FTIR examination of the treated skin samples confirmed that the produced PEs were able to overcome the stratum corneum barrier. These findings suggest that the PEs stabilized with CH/CP nanoparticles provide an effective surfactant-free alternative for the topical delivery of CBD.

Effect of Water Content and Pectin on the Viscoelastic Improvement of Water-in-Canola Oil Emulsions

This study aimed to investigate gelation in glycerol monooleate (GMO)-stabilized water-in-canola oil (W/CO) emulsions by increasing water content (20–50 wt.%) and the addition of low methoxyl pectin (LMP) in the aqueous phase. A constant ratio of GMO to water was used to keep a similar droplet size in all emulsions. Hydrogenated soybean oil (7 wt.%) was used to provide network stabilization in the continuous phase. All fresh emulsions with LMP in the aqueous phase formed a stable and self-supported matrix with higher viscosity and gel strength than emulsions without LMP. Emulsion viscosity and gel strength increased with an increase in water content. All emulsions showed gel-like properties (storage moduli (G’) &gt; loss moduli (G’’)) related to the presence of LMP in the aqueous phase and increased water content. Freeze/thaw analysis using a differential scanning calorimeter showed improved stability of the water droplets in the presence of LMP in the aqueous phase. This study demonstrated the presence of LMP in the aqueous phase, its interaction with GMO at the interface, and fat crystals in the continuous phase that could support the water droplets’ aggregation to obtain stable elastic W/CO emulsions that could be used as low-fat table spreads.

Construction of 3D printed reduced-fat meat analogue by emulsion gels. Part I: Flow behavior, thixotropic feature, and network structure of soy protein-based inks

The fabrication of high-quality low-fat 3D printed foods is strongly dependent on the development of shear-thinning, viscoelastic, and thixotropic ink with a monomodal particle size distribution. In this study, oil was partially or totally replaced with hydrophobically modified biosurfactants (acetylated starch, octenyl succinic anhydride starch, ethyl (hydroxyethyl) cellulose, and dodecenyl succinylated inulin) in a soy protein-based emulsion to produce the desired reduced-fat emulsion gels for potential applications in the 3D printing process. These reduced-fat emulsion gels exhibited pseudoplastic behavior with viscoelastic properties, where viscosity recovery, frequency crossover point, and storage modulus were found to increase with increasing biosurfactants ratio. Higher levels of surface-active biopolymers also yielded inks with lower creep compliance, a smaller droplet size having a more uniform distribution, and possessing improved structural strength and storage stability. Spherical droplets of inks with higher ratios of biosurfactants remained well dispersed. The differences in molecular weight and radius of gyration of biosurfactants accounted for the observed differences in flow behavior and emulsion stability, where inks including dodecenyl succinylated inulin and ethyl (hydroxyethyl) cellulose offered stable structures with strong gel-like properties compared to acetylated and octenyl succinic anhydride starches. All ink networks were also dynamic and recoverable, thus demonstrating the potential of these reduced-fat inks in 3D printing processes.

Electrospun lignin-PVP nanofibers and their ability for structuring oil

This work explores the electrospinnability of low-sulfonate Kraft lignin (LSL)/polyvinylpyrrolidone (PVP) solutions in N,N-dimethylformamide (DMF) and the ability of the different micro- and nano-architectures generated to structure castor oil. LSL/PVP solutions were prepared at different concentrations (8–15 wt%) and LSL:PVP ratios (90:10–0:100) and physico-chemically and rheologically characterized. The morphology of electrospun nanostructures mainly depends on the rheological properties of the solution. Electrosprayed nanoparticles or micro-sized particles connected by thin filaments were obtained from solutions with low LSL/PVP concentrations and/or high LSL:PVP ratios, whereas beaded or bead-free nanofibers were produced by increasing concentration and/or decreasing LSL:PVP ratio, due to enhanced extensional viscoelastic properties and non-Newtonian characteristics. Electrospun LSL/PVP nanofibers are able to form oleogels by simply dispersing them into castor oil at concentrations between 10 and 30 wt%. The rheological properties of the oleogels may be tailored by modifying the LSL:PVP ratio and nanofibers content. The potential application of these oleogels as bio-based lubricants was also explored in a tribological cell. Satisfactory friction and wear results are achieved when using oleogels structured by nanofibers mats with enhanced gel-like properties as lubricants. Overall, electrospinning of lignin/PVP solutions can be proposed as a simple and effective method to produce nanofibers for oil structuring.

Effect of storage on the rheological and viscoelastic properties of mayonnaise emulsions of different oil droplet size

The rheological and viscoelastic properties of mayonnaise emulsions with different size of oil droplets were investigated. Α programmable rotational rheometer was used for the measurements and flow curves were determined at constant and variable shear rate. Mayonnaise exhibited a non-Newtonian, shear-thinning flow with yield stress and time-dependent features. The data from rotational tests were modeled by the Herschel-Bulkley equation. The temperature-dependence of ηa was modelled using the Arrhenius equation. Activation energy, Ea ranged from 15 to 20 kJ/mol. Viscoelastic properties were characterized using small amplitude oscillatory shear. Mayonnaise exhibited weak gel-like properties. The values of apparent and complex viscosity were correlated using the generalised Cox-Merz rule. According to the obtained values of parameter α, this rule could not be cut-down to one-parameter linear function. The rheological characteristics of mayonnaise were well correlated to the size of oil droplets.

Probing the Dynamic Covalent Chemistry Behavior of Nitrogen-Centered Di- and Triurazole Radicals.

Dynamic covalent chemistry (DCvC) describes systems in which readily reversible bond formation allows for control of product distributions by straightforward manipulation of reaction conditions (e.g., changes in temperature, solvent, concentration, etc). Nitrogen-centered 1-aryl urazole radicals reversibly form tetrazane dimers in solution via N-N bond formation. When two such urazole units are attached to a single, appropriately substituted benzene ring, the resulting diradical system engages in DCvC. At room temperature, a polymeric network of units is created that exhibits gel-like properties, while at higher temperatures, near quantitative dimerization to form a molecular cage is observed.However, attaching three such urazole units to a single appropriately substituted benzene ring inhibits DCvC behavior.

Micronized apple pomace as a novel emulsifier for food O/W Pickering emulsion.

In order to develop natural, food-grade particles as emulsifiers, wet-milled has been conducted to obtain apple pomace particles in varying sizes. Structural characteristics, physicochemical properties and Pickering emulsifying potential of the particle in different sizes were investigated. Particle size of apple pomace was gradually reduced from 12.9μm to 550nm during 8h milling. With the decrease of particles size, the morphology became less angular. Meanwhile, some insoluble dietary fibers transformed into soluble ones, and the wettability tended to be hydrophilic, therefore, the water and oil holding capacities and free-radical-scavenging capacities increased. The properties of Pickering emulsions stabilized by wet-milled apple pomace particles in different sizes were then investigated. The decrease of particle size resulted in the size reduction of emulsion droplets, and gave rise to enhance gel-like properties and antioxidative activities of emulsions. The results demonstrated promising prospect of wet-milled apple pomace particles as emulsifiers in food industry.

Amines used for low temperature curing of PDMS-based gel-networks impact γ-irradiation outcome

Four structurally different amines: 1,3-diamino-2-propanol (DAP), diethylenetriamine (DETA), tris(2-aminoethyl)amine (TAEA) and triethylenetetramine (TETA) were reacted with diglycidyl ether terminated poly(dimethylsiloxane) (PDMS-DGE) at relatively low temperature of 50 °C. Stable transparent networks with gel-like properties but without a liquid component, “gel-networks” were obtained. Raman spectra revealed presence of residual epoxy-group absorptions in cured gel-networks but secondary amine absorption intensities in FTIR spectra were used for monitoring of the curing reaction extent. To assess their radiation stability gel-networks were gamma-irradiated to absorbed dose of 50 kGy. Even though contribution of amine segments to PDMS-based gel-networks is relatively small, their structure significantly influenced the properties of studied PDMS-based gel-networks. The most important property of an amine was the ability to either form hydrogen bonds, or produce denser network like a triamine. However there were also significant differences in properties of gel-networks prepared with mutually similar diamines DETA and TETA that can be considered a dimer and a trimer of ethylenediamine. In the studied gel-networks there is a complex interaction of extent of initial curing that depended on the amine used and the resulting (dis)order that strongly influenced the outcome of irradiation. An endothermic transition presumably caused by reversible gel-network collapse was observed in DSC thermograms of all the gel-networks. Its temperature depended on the amine type and shifted to higher values on irradiation. Changes in most properties like residual gel content on extraction or DC electrical conductivity and its frequency dependence were more pronounced in gel-networks prepared with diamines DETA and TETA than in those prepared with amines capable of significant secondary valent interactions (DAP and TAEA). Radiation curing and/or crosslinking seem to have occurred only in TETA-cured gel-network and it was mostly due to lower extent of initial reaction. Since swelling is a measure of gel quality and it was higher in irradiated gel-networks it may be concluded that irradiation to D = 50 kGy improved their properties.

Reversible Mechanical Regulation and Splicing Ability of Alginate-Based Gel Based on Photo-Responsiveness of Molecular-Level Conformation.

In this study, benefiting from the sensitive molecular conformation transversion in azobenzene, a new strategy for fabricating alginate gels with the abilities of splicing and photo-responsive mechanical adjustment is reported. Firstly, a 4,4’-azobis(benzoylhydrazide) (Azo-hydrazide) linker was used to crosslink alginate physically via the electrostatic interaction between hydrazide groups and carboxyl groups. It was then shaped and transferred in situ to a chemically crosslinked gel via 450 nm light irradiation. Under the irradiation, the molecular conformation change of azobenzene in the linker was able to form covalent bonds at the crosslinking points of the gels. Furthermore, the reversible conformation transformation of azobenzene was able to induce the increase and decrease of the storage modulus under irradiation with 365 nm light and 450 nm light, respectively, while also providing gel-like mechanical properties, depending upon the irradiation time and given wavelength. Meanwhile, the results also indicated that active groups could contribute to the splicing ability of the gel and construct a hollow cavity structure. It is believed that this work could provide a versatile strategy for preparing photo-responsive gels with reversibly tunable mechanical properties.

Effect of pH on the viscoelastic properties of pig gastric mucus

Mucus is a biomaterial with peculiar, gel-like viscoelastic properties, and bearing different functionalities, depending on the different mucosae it covers. It is clear that these functionalities have to stay effective throughout the in vivo broad range of physiological pH values at which the mucus is exposed. We sought here to determine the effect of pH on the rheological properties of ex vivo mucus. We demonstrate that viscoelastic properties of gastric mucus are quite “stable” to pH changes, in marked contrast with the pH sensitivity of purified mucin gels. We also find that the rheological features of porcine gastric mucus are reversible when the system is first alkalized up to solubilization (pH > 8.5) and then re-acidified to its initial pH value.