Cryo-SEM Images Research Articles

Thermosensitive Hybrid Elastin-like Polypeptide-Based ABC Triblock Hydrogel

We report the synthesis of a well-defined hybrid ABC triblock terpolymer containing a synthetic poly(trimethylene carbonate) (PTMC) block A and a thermosensitive BC diblock of recombinant elastin-like polypeptides (ELPs). The triblock in diluted solution (0.1–0.3% w/v), at low temperatures in ultrapure water, forms micellar structures of 10–60 nm sizes in diameter as characterized by dynamic light scattering (DLS) and liquid atomic force microscopy (AFM). While heated above its transition temperature (Tt), larger particles of 200–300 nm sizes are obtained, consistent with the formation of coacervates. When concentrated, the viscosity of the triblock copolymer solution progressively increases, giving a free-standing gel at 4% w/v formed by a network of micron-sized particles. The formed hydrogels are thermally reversible, and their sol–gel transitions are fast and sharp. The gel formation mechanism appears to interestingly biomimic tropoelastin, the native monomeric form of natural elastin, as demonstrated by optical and cryogenic-scanning electron microscopy (cryo-SEM) imaging.

Effect of κ‐carrageenan/milk protein interaction on rheology and microstructure in dairy emulsion systems with different milk protein types and κ‐carrageenan concentrations

We investigated the effect of κ-carrageenan (κ-CG) addition and supplementation with Na-CN, WPI, and MPI on the rheological properties, microstructure, fat globule size distribution, and stability of low-fat cream (LFC) emulsions containing 19% milk fat. Rheological parameter (ηa,10, K, and G′) values of LFCs increased with κ-CG addition. At 0.1% κ-CG concentration, MPI-stabilized LFC had higher G′ value (64.8 Pa) than those of WPI-stabilized LFC (51.3 Pa) and Na-CN-stabilized LFC (34.8 Pa), indicating the strong interaction between MPI and κ-CG. Cryo-SEM images showed the protein layers on milk fat globule membrane in dairy emulsions and revealed that κ-CG led to depletion-flocculation of milk fat globules and promoted clustering of globules. The creaming index values of LFCs with 0.10% κ-CG were lower than those of LFCs with 0.05% κ-CG. Thus, high κ-CG concentrations can contribute to the physical stability in dairy emulsions stabilized by milk proteins. Practical applications Milk proteins are widely used as emulsifiers, and κ-carrageenan (κ-CG) is added to dairy emulsion products to improve their physical properties and stability. Therefore, in this study, the effect of κ-CG addition on physical properties and stability of low-fat creams (LFCs) supplemented with different milk protein types (Na-CN, WPI, and MPI) was investigated. The strong synergistic interaction between proteins and κ-CG was observed in MPI-stabilized LFCs when compared to Na-CN- and WPI-stabilized LFCs. We found that the presence of κ-CG in MPI-stabilized LFCs improved the stability of LFCs by inhibiting the phase separation due to the high viscosity of the continuous phase. These findings suggest that dairy cream-based food products with desirable physical properties can be realized through κ-CG addition to LFC emulsions with milk proteins such as ice cream mix, coffee creamer, and light cream.

Synthesis and Characterization of Psyllium Polysaccharide–Poly(2-hydroxypropyl methacrylate)−Poly(acrylamide) Hydrogels for Use in Sustained Drug Delivery Applications

Psyllium has been explored for various food and pharmaceutical applications. Recently, its therapeutic action against cancer has been reported. Hence, herein in this research it has been modified to develop hydrogels through graft copolymerization reaction for use as sustained drug delivery carriers for anti-cancer drug “5-fluorouracil” (FU) to enhance the therapeutic potential. Synthesis of hydrogels was carried out by grafting of poly(2-hydroxypropyl methacrylate) and poly(acrylamide) onto psyllium in the presence of crosslinker. Polymers were characterized by cryo-SEM, AFM, XRD, 13C-NMR, and TGA techniques, beside evaluation of swelling, drug release, blood compatibility, mucoadhesion, antioxidant properties and gel strength of the hydrogels. The porous network structure with rough surface was observed in cryo-SEM and AFM images of the samples. Release of FU from psy-cl-poly(HPMA-co-AAm) polymer occurred with non-Fickian diffusion in sustained manner. These hydrogels were mucoadhesive (work of adhesion = 8.45 ± 0.32 N mm), non-haemolytic (haemolytic index = 1.05 ± 0.07%), and antioxidant (with 19.12 ± 0.14% inhibition in DPPH assay) in nature, therefore they could be used as slow drug delivery carriers for ailments associated GIT system.

Analyzing the microstructure of a fresh sorbet with X-ray micro-computed tomography: Sampling, acquisition, and image processing

Abstract X-ray micro-computed tomography and image processing techniques were used to analyze fresh frozen sorbets at the outlet of a batch freezer. Sorbets made from water and sucrose were visualized and their microstructure was quantified with a resolution of 9 μm. Sodium iodide was confirmed to enhance the contrast between the unfrozen water and ice in sorbets. A thermostated box was employed to keep the samples at frozen state and constant temperature (close to −6 °C) during imaging. A reproducible quantification of size distributions and volume fractions of ice crystals and air bubbles were obtained. Data concerning ice crystals were in agreement with cryo-SEM imaging. Ice crystals represented approximately 50%wt of the product and their mean size was about 60 μm whereas air bubbles represented about 6% of the volume. Finally, X-ray microtomography equipped with a thermostated box was found to be a particularly relevant technique for the analysis of the microstructure of frozen desserts.

Size effect of carboxymethyl chitin nanocrystals on the properties of foams in aqueous surfactant solutions

Size effect of carboxymethyl chitin nanocrystals on foam stability and foaming ability in aqueous surfactant solutions was investigated. The chitin nanocrystals (CNC) were synthesized by 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) oxidation of α-chitin at pH 10∼11 with ultrasonic treatment. The sizes of chitin nanocrystal (CNC) were controlled by adding different amounts of NaClO during the TEMPO oxidation reaction. Since the surface of CNC was negatively charged, the aqueous foams prepared by cationic cetyltrimethylammonium bromide (CTAB) surfactant and CNC showed good foam properties. The CNC was also freeze-dried to confirm the effect of surface charge and hydrophobicity in foam. With the freeze-dried CNC, foamability was increased by lowering the size of CNC, but foam stability was decreased. On the other hand, with the non-freeze-dried CNC, foam stability was increased but foaming ability was decreased by lowering the size. The Cryo-SEM images demonstrated that CNCs were well adsorbed at air/water interface in foam, and improved foam stability.

Surface Density of the Spongy and Palisade Parenchyma Layers of Leaves Extracted From Wideband Ultrasonic Resonance Spectra.

The wide band and air-coupled ultrasonic resonant spectroscopy together with a modified Simulated Annealing metaheuristic algorithm and a 1D layered acoustic-model are used to resolve the structure of plant leaves. In particular, this paper focuses on the extraction of the surface density of the different layers of tissue in leaves having a relatively simple structure. There are three main reasons to select the surface density as the focus of this study: (i) it is a parameter directly extracted by the proposed technique and it requires no further processing, (ii) it is relevant in order to study the dynamic of the water within the different tissues of the leaves and also to study the differential development of the different tissues, and (iii) unlike other parameters provided by this technique (like resonant frequency, impedance, ultrasonic elastic modulus, or ultrasonic damping), this parameter can be easier to understand as it is a direct measure of mass per unit surface. The selection of leaves with a simple structure is justified by the convenience of avoiding an unnecessary complication of the data extraction step. In this work, the technique was applied to determine the surface density of the palisade and spongy parenchyma layers of tissue of Ligustrum lucidum, Vitis vinifera, and Viburnum tinus leaves. The first species was used to study the variation of the surface density at full turgor with the thickness of the leaf, while the two other species were used to study the variation of the surface densities with the variation in the leaf relative water content. Consistency of the results with other conventional measurements (like overall surface density, and cross-section optical and cryo-SEM images) is discussed. The results obtained reveal the potential of this technique; moreover, the technique presents the additional advantage that can be applied in-vivo as it is completely non-invasive, non-destructive, fast, and equipment required is portable.

Graft copolymerization of polyvinylpyrollidone onto Azadirachta indica gum polysaccharide in the presence of crosslinker to develop hydrogels for drug delivery applications

In this work, graft-copolymerization of poly vinylpyrollidone onto Azadirachta indica gum polysaccharide in the presence of crosslinker has been carried out to prepare the hydrogel for use in drug delivery. The polymers were characterized by cryo-SEM, AFM, FTIR, and 13C NMR. The gel strength, cross-link density, mesh size, thrombogenicity, antioxidant and mucoadhesion properties of the gum-PVP hydrogels were determined along with the evaluation of drug release profile of methyl prednisolone, a colonic anti-inflammatory agent, from the drug loaded hydrogels. Cryo SEM images showed the porous crosslinked structure of the polymer network. The drug release from the polymer followed non-Fickian diffusion mechanism. The polymers showed 71.47 ± 4.63% haemo-compatibility and 05.52 ± 0.59 Nmm gel strength. The value of DPPH radical scavenging assay (73.16 ± 04.85%) indicated that the gum-PVP polymers are antioxidant. The results of biocompatibility, antioxidant activity, mucoadhesion and drug release properties of the polymers inferred the use of this drug carrier for colonic drug delivery.

Impact of additives with opposing effects on the rheological properties of bentonite drilling mud: Flow, ageing, microstructure and preparation method

Drilling fluids are formulated with a range of additives to achieve the desired functional properties including specific rheological properties. Its rheology, a critical property, is sensitive to the chemicals used in its formulation and the environment encountered during drilling. The flow and time-dependent behaviour of bentonite slurries were evaluated under the influence of KCl and P2O74− or MgCl2 and P3O105− at specific concentrations. The multi-charge phosphate anions weakened the gel and its ageing behaviour at low KCl or MgCl2 content. At high KCl concentration, the sequence of salt addition in the gel preparation has a significant effect on the gel strength and stability. The gel was very strong when the platelets were allowed to exfoliate before the salt addition. When the delamination was hindered, a weak and at time an unstable gel was produced as a result of low platelet concentration. The gels prepared by both methods displayed time-independent behaviour at high KCl concentration. The ageing behaviour was described well by the Leong model. The cryo-SEM images revealed different microstructures and particle interaction configurations between gels with low and high salt concentration containing 0.5 dwb% P2O74−. The phosphate-based additives adsorbed at the platelet edge and weakened the platelet-platelet attraction at the network junctions. The opposing effect of Mg2+ at 0.01M to the effect of 0.5 dwb% dwb% P3O105− on the rheological properties of the bentonite gel is weak.

Swelling acidic poly(ionic liquid)s as efficient catalysts for the esterification of cyclohexene and formic acid

Acidic poly(ionic liquid)s (PILs) with swelling ability were synthesized by free radical copolymerization of N-vinylimidazolium ionic liquids, divinylbenzene (DVB) and sodium acrylate (NaAA), and further acidification by sulfuric acid. The swelling ability of acidic PILs was greatly affected by cross-linker content and chain length of 3-alkyl-substituents on imidazolium. Cross-linked network structures could be observed from the cryogenic scanning electron microscopy (cryo-SEM) images of the swollen acidic PILs in formic acid. Acidic PILs with network structures in swollen state exhibited excellent activities in the esterification of cyclohexene and formic acid, and the catalytic activities were in positive correlation with their swelling abilities. Acidic PIL with 3-octyl-substituent and 2.5 mol% DVB (PIL-C8-2.5DVB-HSO4) had the highest swelling ability in formic acid and exhibited comparable catalytic activities with homogeneous catalysts such as sulfuric acid and p-toluenesulfonic acid.

Dissipative Self-Assembly of Dynamic Multicompartmentalized Microsystems with Light-Responsive Behaviors

Summary Living cells are compartmentalized systems operating far from thermodynamic equilibrium and consume energy from the environment to carry out their functions. The construction of biomimetic synthetic compartments has both scientific and technological value. Despite many advances, the assembly of synthetic compartments that present nonequilibrium behaviors based on dissipative (or transient) self-assembly remains a grand challenge. Here, we describe the design and synthesis of multicompartmental systems with an active microstructure and complex behaviors. By including an artificial pathway for energy dissipation, we demonstrate the autonomous generation of active polymeric systems using a strategy based on polymerization-induced self-assembly (PISA), driven by chemical fuel. Remarkably, these self-organized synthetic systems exhibit a dynamic change in their multicompartmental structures when exposed to light. This work introduces a strategy toward the design and construction of synthetic compartments with a dynamic structure and also presents pathways to engineer materials with spatially controllable structures and functionalities.

Aggregation-Induced Emission and Organogels with Chiral and Racemic Pyrene-Substituted Cyanostyrenes.

The synthesis, photophysical investigations, and organogel formation of pyrene-phenyl acrylonitriles (1-6) bearing mono-, di-, and trichiral and racemic substitutions were studied. The molecules self-assemble in water and show remarkable emission wavelength and intensity changes associated with distinct color changes. Cryo-scanning electron microscopy (Cryo-SEM) images show the formation of uniform nanoaggregates for the monosubstituted derivatives and network-like structures for di- and trisubstituted derivatives. The favorable π-π stacking ability of the coplanar pyrene ring, steric restrictions due to the cyano group, and beneficial noncovalent interactions from the citronellol moiety allow the molecules to form excellent organogels with fibrous and twisted ribbon morphology for the racemic and chiral derivatives. The organogels based on small molecules could be of high relevance for potential investigations involving soft biological matter.

Characterization of interfacial interactions and emulsification properties of bicarbonate solutions and crude oil and the effects of temperature and pressure

Abstract An extensive study of fluid/fluid interactions of bicarbonate solutions and crude oil from Danish North Sea has been carried out. Interfacial tension (IFT) measurements, and oil/brine contact tests were conducted. Brine with salinity of 0.05 M was shown to be the optimum salinity in emulsification at basic pH of bicarbonate solution. ATR-FTIR spectra of oil and formed emulsions were recorded to characterize the nature of the emulsion. Information about the content of polar molecules and the water content of the emulsions was provided by the IR analysis. The emulsion structure and drop size which correspond to the optimum salinity were characterized using cryo-scanning electron microscopy (Cryo-SEM) images. The emulsion drop size was comparable to carbonate pore size. This suggests that flow diversion by emulsion formation is possible as a mechanism with an impact on oil recovery. In flow diversion mechanism, formed emulsions will plug fractures and bigger pores and redirect the injected brine to the non-flooded zones. IFT was measured at reservoir pressure (200 bar) and different temperatures (23, 60, 90 and 120 °C). Overall, the change in interfacial tension values in compared to formation water was up to 30% and rarely exceeded that. At each temperature, the IFT has been reduced to the lowest achievable value and no further reduction was observed by increasing the salinity. Furthermore, an increase in temperature led to additional reduction in IFT for each salinity.

Effect of microencapsulated fish oil powder on selected quality characteristics of chicken sausages.

Encapsulation of fish oil for use as oil powder for the human food industry offers new product design possibilities. The fat content of fish is unique in the amount of of long chain n-3 fatty acid that it contains. It can be expected that developing innovative food products with significantly improved nutritional value can simultaneously affect their rheological and sensory qualities in different ways. The present study aimed to compared the influence of the addition of fish oil and microencapsulated fish oil on the mechanical, structural, and sensory properties of poultry sausages during 21-day storage. In comparison with other systems, sausages enriched with microencapsulated fish oil were characterized by a greater capacity to accumulate potential strain energy (G') and by statistically significantly greater hardness measured in all the storage periods that were tested. The sausages enriched with microencapsulated fish oil were characterized by higher water activity than the other sausage variants. The analysis of cryo-scanning electron microscopy (cryo-SEM) images indicated the presence of a large evenly dispersed oil phase and microcapsules in the structure of the sausages. The sample with the addition of microcapsules was characterized by higher values on the smell and consistency parameters. The better results in the sensory evaluation of the structural parameters of the sample with microcapsules were consistent with the results of instrumental assessments. The use of microencapsulated fish oil powder as an ingredient of chicken sausages therefore seems to be a promising concept. © 2019 Society of Chemical Industry.

Application of graphene oxide nanosheets and HPAM aqueous dispersion for improving heavy oil recovery: Effect of localized functionalization

Using efficient methods to recover heavy oil is crucial for economic success. Polymer flooding is a very efficient way to sweep oil reservoirs at both macroscopic and microscopic scales by increasing the viscosity of injected water. Recently, it was shown that addition of nanomaterials to polymer solutions may improve the flooding performance and recovery. In this work, two different types of graphene oxide (GO) nanofillers with different different location of OH group functionalization (functionalization mainly on basal plane (S-GO) and functionalization mainly on the edges (E-GO)) were synthesized to improve the rheological behavior and oil recovery efficiency of a partially hydrolyzed polyacrylamide (HPAM) solutions. To characterize the chemical structure of both GOs, thermogravimetric analysis (TGA) and Raman spectroscopy were employed. Frequency sweep, creep, creep recovery, shear start-up, and strain sweep tests were also utilized to evaluate the viscoelastic behavior of HPAM solutions, with or without the nanofillers in both linear and nonlinear viscoelastic regions. Cryo-SEM images of the hybrid dispersion of HPAM/GOs were captured to assess the dispersion state of all systems. A core flooding set up was used to evaluate the effectiveness of all dispersions in improving the viscous oil recovery by polymer injection. Rheological properties showed that addition of 0.2 wt% of both GOs reduced dynamic moduli. However, due to the better dispersion of S-GO in a HPAM solution, incorporation of 0.2 wt% of S-GO to the HPAM solution, improved the oil recovery by 7.8% compared to the HPAM solution.

Fragmentation of compact polymer-bridged flocs in the laminar taylor vortex flow regime: population balance and breakage function

The breakage or fragmentation kinetic function (FKF) of a given father size floc breaking to form two specific daughter size flocs cannot be measured experimentally. Indirectly it can be determined from the FKF model used to solve the dimensionless log-form population balance (PB) equation for floc fragmentation subjected to meeting three conditions: i) the computed and experimental particle size distribution function (PSDF) matched at all fragmentation time, ii) the PSDF data at zero fragmentation time was the input in the computation and iii) the duration of the experimental fragmentation be used in making the PB equation dimensionless. The fragmentation of compact polyelectrolyte-bridged silica flocs in a narrow gap concentric cylinder flow cell was investigated in the laminar Taylor vortex flow regime. The FKF data was correlated with the Taylor number. The FKF values were much smaller for large flocs as they tend to migrate to the low shear region. Cryo-SEM images of the flocs at different fragmentation times showed compact fractal structure with dimension larger than 2.

The development of a direct approach to formulate high oil content zein-based emulsion gels using moderate temperatures

The current research presents an effective direct route to obtain high oil content zein-based emulsion gels at moderate temperatures that is feasible for large-scale production. The preparation procedure involved the dissolution of zein in 90% (w/w) aqueous ethanol, followed by addition of glycerol and oil, and finally heating at ~90 °C to induce ethanol evaporation which promotes zein self-assembly and aggregation. The CLSM and cryo-SEM images confirmed the formation of nanoscale spherical zein aggregates organized on the oil droplet interface while excess proteins form a continuous percolating network between the oil droplets. The coiled-coil conformation of zein particles and the role of hydrogen bonds leading to the formation of a zein network through association of spherical zein particles were confirmed using infra-red spectroscopy and temperature-dependent rheology, respectively. Hard gel (4 °C) to soft gel (90 °C) transition was observed in a temperature ramp rheology experiment, indicating strengthening and weakening of hydrogen interactions between the particulate protein aggregates. Similar hydrogen bond breakdown and reformation was observed in a thixotropy experiment while applying high shear and withdrawal, respectively. Stability studies revealed glycerol syneresis, resulting in the deterioration of the gel's mechanical properties due to increase in hardness and decrease in cohesiveness at room temperature. Overall, these results provide important insight into the gelation mechanism and gel characteristics of zein-stabilized emulsion gels prepared by a direct route under moderate temperature conditions, which can be used for various food applications.

Freezing and sublimation effects on cryo-SEM imaging and microanalysis

Freezing and sublimation effects on cryo-SEM imaging and microanalysis

A novel electrically conductive water borne epoxy nanocomposite coating based on graphene: facile method and high efficient graphene dispersion

In this work, we present a novel method to exfoliate graphite to graphene oxide nanosheets with single to 3 layers at concentration as high as 15 mg/ml. In the first step, graphite intercalated compound (GIC) was obtained through a chemical intercalation process. In the next step, GIC was expanded and used as the precursor to obtain oxidized graphite. Oxidized graphite was introduced into a high alkaline medium and a high-speed homogenizer was used to complete the exfoliation process. Raman spectroscopy, XPS, XRD, TGA, SEM and TEM were used to characterize the synthesized graphene oxide nanosheets. Electrically conductive coatings were prepared by adding and stirring graphene oxide dispersion into an epoxy-hardener pre-mixture. The prepared coatings were post cured at 100 °C followed by annealing at 225 °C to in situ reduce the incorporated graphene oxide to graphene nanosheets. High electrical conductivity values as 0.5 S/m was obtained for the epoxy-graphene nanocomposite at graphene loading level of 1.5 wt%, which is comparable to previously reported data using more complex and laborious fabrication methods. Cryo-SEM images were captured in the liquid phase to investigate electrical network formation in the polymeric matrix.

Oxidative stability and physical properties of mayonnaise fortified with zein electrosprayed capsules loaded with fish oil

This study investigated the oxidative stability and physical properties of low-fat mayonnaise fortified with electrosprayed zein capsules loaded with fish oil. A high encapsulation efficiency (EE) (83 ± 1%) was achieved in the encapsulates and semi-spherical capsules with rough surface and mean diameter of 2.4 ± 0.7 μm were obtained. The amount of primary oxidation products of the zein capsules did not increase over the storage, even though the initial content was higher compared to neat fish oil. Cryo-SEM images revealed that the capsules remained intact when they were incorporated into a water-based food matrix like mayonnaise. This explained the lower content of hydroperoxides at the end of the storage for the capsule-enriched mayonnaise (Mayo-C) when compared to mayonnaise enriched with neat fish oil (Mayo-F) (2 meq/kg oil vs. 6 meq/kg oil, respectively). Even though, volatile compounds from the secondary oxidation of omega-3, such as 2-ethylfuran and 1-penten-3-one were found in higher amounts in Mayo-F, a higher overall increase in all other secondary oxidation products was observed in Mayo-C. This increase was attributed to the formation of oxidation volatile compounds from the zein material, together with the oxidation of un-encapsulated fish oil droplets. Moreover, Mayo-C presented higher viscosity and droplet size than Mayo-F, which also increased during storage, although no further alterations of the emulsion like creaming were observed. Overall, these findings indicate the benefits of using zein as hydrophobic shell material for the development of omega-3 loaded-electrosprayed capsules intended to the enrichment of water-based food matrices when compared to the use of hydrophilic wall materials.

Synthesis and application of vinyl lactam block copolymer as kinetic hydrate inhibitors

In this paper, a novel block copolymer poly (N-vinyl caprolactam)-co-acrylamide) (PVCap-co-AM) was made from N-vinyl caprolactam (NVCap) with acrylamide (AM) by living radical copolymerization. The kinetic inhibitory performance of PVCap-co-AM on CH4 hydrate formation was firstly investigated and compared with PVP and PVCap. The results indicated that higher-cloud-point PVCap-co-AM behaved better than PVCap under the same conditions. Powder X-ray diffraction (PXRD) spectroscopy and Raman spectroscopy showed structure I hydrate was formed with and without KHIs. However, compared to pure water, the presence of KHIs reduced the ratio of large to small cage occupancy by CH4. The stronger inhibition activity, the value became lower. Cryo-SEM images illustrated the morphology of CH4 hydrate crystals formed significantly varied by KHIs, which could be helpful for pipeline fluids safe transportation.