Elastic Network Structure Research Articles

Caffeine weakens the astringency of epigallocatechin gallate by inhibiting its interaction with salivary proteins

The astringency of green tea is an integrated result of the synergic and antagonistic effects of individual tea components, whose mechanism is highly complex and not completely understood. Herein, we used an epigallocatechin gallate (EGCG)/caffeine (CAF)/saliva model to simulate the oral conditions during tea drinking. The effect of CAF on the interaction between EGCG and salivary proteins was first investigated using molecular docking and isothermal titration calorimetry (ITC). Then, the rheological properties and the micro-network structure of saliva were studied to relate the molecular interactions and perceived astringency. The results revealed that CAF partially occupied the binding sites of EGCG to salivary proteins, inhibiting their interaction and causing changes in the elastic network structure of the salivary film, thereby reducing astringency.

The construction of Moringa oleifera seed protein emulsion: in vitro digestibility and delivery of β-carotene.

β-Carotene (BC) is difficult to apply effectively in the food industry due to its low solubility and bioavailability. This work aimed to fabricate Moringa oleifera seed protein (MOSP) stabilized emulsions as delivery vehicles for BC and investigate the effect of aqueous phase conditions including pH and ionic strength on this system. All MOSP samples were positively charged and the particle size of MOSP increased with the increase of pH. At pH 5.0 and 0.2 mol L-1 sodium chloride (NaCl), the MOSP emulsion demonstrated the highest stability coefficient and minimal creaming index, while exhibiting a lower release rate in vitro digestion. The rheological behavior of all MOSP emulsions within the frequency range of 0.1-10 Hz was dominated by viscoelasticity, forming an elastic network structure through dispersed droplets. Additionally, the MOSP emulsion loaded with BC prepared at pH 5.0 and 0.2 mol L-1 NaCl displayed enhanced ultraviolet light stability (52.31 ± 0.03% and 51.86 ± 0.05%) as well as thermal stability (72.39 ± 8.67% and 86.78 ± 10.69%). Furthermore, the BC in the emulsion at pH 7.0 exhibited favorable stability (65.14 ± 0.02%) and optimal bioaccessibility (40.30 ± 0.04%) in vitro digestion. The results provided reference data for utilizing MOSP as a novel emulsifier and broadening the application of BC in the food industry. © 2024 Society of Chemical Industry.

Carboxymethyl chitosan-glycerol multi-aldehyde based self-healing hydrogel system

The superiority of self-healing hydrogel systems with dynamic covalent chemistry is the ability to establish the gel network structure despite changes in ambient conditions such as pH, temperature, and ion concentrations. The Schiff base reaction, which occurs through aldehyde and amine groups, allows dynamic covalent bonds at physiological pH and temperature. In this study, gelation kinetics between glycerol multi-aldehyde (GMA) and water-soluble form of chitosan, carboxymethyl chitosan (CMCS), has been investigated, and the self-healing ability has been evaluated in detail. Macroscopic and electron microscope-based visual inspection and rheological tests showed that the hydrogels exhibit the highest self-healing capacity at 3–4 % CMCS and 0.5–1 % GMA concentrations. Hydrogel samples were subjected to alternating high and low strains to deteriorate and rebuild the elastic network structure. The results showed that hydrogels could restore their physical integrity after applying 200 % strains. In addition, direct cell encapsulation and double staining tests showed that the samples do not possess any acute cytotoxicity on mammalian cells; hence, hydrogels could potentially be used in tissue engineering applications for soft tissues.

Low density lipoprotein-pectin complexes stabilized high internal phase pickering emulsions: The effects of pH conditions and mass ratios

The present work aimed to explore the feasibility of using egg yolk low density lipoproteins (LDL) as naturally occurring nanoparticles to prepare high internal phase Pickering emulsions (HIPEs), and to understand the role of pectin (PE) as a natural food thickener in improving the emulsifying stability to prepare HIPEs. Colloidal complexes were formed spontaneously via electrostatic interactions upon mixing PE and LDL at acidic pH condition. The colloidal characteristics of LDL-PE complexes were studied by dynamic light scattering method, Fourier transform infrared spectroscopy and viscosity measurements, as well as interfacial activities. Lastly, the capability of complexes as a stabilizer to prepare HIPEs was then comprehensively investigated as functions of pH conditions and mass ratios of LDL and PE. The results indicated that the particle sizes and surface activities of LDL-PE complexes were highly dependent on the electrostatic interactions. The interactions between LDL and PE slightly reduced at neutral pH conditions or higher concentrations of PE, which were more favorable to form stable particles with smaller size and higher surface activity, and thus greater stability of HIPEs. Although the interfacial tensions of LDL increased with the existence of PE, the stability of LDL-PE stabilized HIPEs (LP-HIPEs) was greatly enhanced compared with the free LDL stabilized ones. LDL and PE formed non-covalent network among the emulsion droplets and the oil-water interface of HIPEs, inducing stable gel structure. Droplet size analysis and morphological observation under optical microscopes together with digital photos revealed the homogenous emulsion droplets in a strong gel geometry. Gel-like elastic network structure was confirmed by rheological measurements, and the thick coating layer of LDL-PE complexes on the oil-water interface was further visualized by confocal laser scanning microscope. Our findings are innovative and offer new opportunities to prepare HIPEs from all natural ingredients for future applications in the food industry. • Low density lipoprotein-pectin (LDL-PE) complexes were able to stabilize HIPEs. • Pectin played critical roles in the formation of stable gel-like structure in HIPEs. • Rheological data and microscopical images confirmed the strong gel network. • The HIPEs showed exceptional stability in centrifugation and long-term storage tests. • LDL-PE exhibited superior emulsifying and stabilization capability than LDL alone.

The Impacts of Different Pea Protein Isolate Levels on Functional, Instrumental and Textural Quality Parameters of Duck Meat Batters.

This study aimed to investigate the effect of pea protein isolate (PPI) on the functional, instrumental and textural quality parameters of duck meat batters (DMB). Ground duck breast meat was mixed with different concentrations of PPI (0%, 3%, 6% or 9%, w/w) to prepare DMB. The color, cooking yield, water-holding capacity, water distribution and migration, rheological properties and texture profile of the DMB were evaluated. The results showed that the L* value of the gel decreased and the b* value increased with the increasing pea protein addition. The cooking yield and water-holding capacity showed a gradual increase, but the difference was not significant (p > 0.05). Compared with the control, the storage modulus (G′) and loss modulus (G″) were higher at the beginning and at the end and increased with the addition of pea protein, which was in accordance with the Fourier series relationship. The hardness, chewiness and gumminess of the gels gradually increased; on the contrary, the springiness and cohesiveness first increased and then decreased, respectively, reaching a maximum value of 0.96 and 0.81 when the addition amount reached 6%. Adding pea protein to the gels not only increased the area of immobilized water but also decreased the area of free water, thus improving the water-holding capacity of the batters. Therefore, pea protein can promote the formation of a stable and elastic network structure of duck meat batters.

Molecular structure and functional properties of glycinin conjugated to κ-carrageenan and guar gum: A comparative study

Molecular structure and functional properties of glycinin conjugated to κ-carrageenan and guar gum using a dry-heating method were comparatively analyzed. Glycosylation was confirmed by analyzing the degree of grafting, protein subunit composition, infrared absorption profile, and changes in contents of protein secondary structures. K-carrageenan was proven to possess a greater susceptibility to be grafted to glycinin than guar gum due to its relatively low molecular weight and negatively charged characteristics. The improvement of solubility by glycosylation with guar gum near the isoelectric point of glycinin was better than that by glycosylation with κ-carrageenan. Glycinin glycosylated with both polysaccharides exhibited enhanced emulsifying activity and stability. The enhanced apparent viscosity, elastic modulus, and viscous modulus also demonstrated that glycosylation promoted the appearance of stable elastic network structure. In summary, glycosylation with these two polysaccharides conferred glycinin superior emulsifying and rheological properties, and κ-carrageenan exhibited a better performance compared to guar gum.

Experimental Investigation of Mechanical, Permeability, and Microstructural Properties of PVA-Improved Sand Under Dry-Wet Cycling Conditions

To improve the stability of sand slopes in Southeast Tibet, the wet–dry cycle test, immersion test, and permeability test were carried out using polyvinyl alcohol (PVA) as the improving material. The improvement effect was evaluated by considering the unconfined compressive strength. The results have revealed that the unconfined compressive strength of the improved soil significantly increased with the PVA content, while the degradation of the improved soil by wet–dry cycling and water immersion weakened. However, the permeability of the improved soil slightly decreased compared with that of unmodified soil. Through scanning electron microscopy (SEM), it was found that PVA only forms an elastic network structure in the sand to wind and connect the soil particles, but pores remain in the sand. This indicates that the addition of PVA does not affect the permeability to a great extent but greatly increases the strength. The findings of this study provide a useful reference for the practical application of PVA.

In Situ-Formed Novel Elastic Network Binder for a Silicon Anode in Lithium-Ion Batteries.

High energy density lithium-ion batteries with preferable cycling stability are critical for the development of all-electric vehicles. Silicon (Si) has demonstrated a remarkable potential for application as anode materials due to its superior capacity performance and worldwide abundance. However, Si intrinsically undergoes substantial volume fluctuation during repeated lithiation/delithiation processes, which pulverizes the Si particles and undermines the integrity of the electrode structures, thus resulting in frustrating cycling stability. We developed a polymer binder with a highly stretchable and elastic network structure that can accommodate volume variation of Si. This was realized by an in situ cross-linking of polyacrylic acid (PAA) with isocyanate-terminated polyurethane oligomers that consist of polyethylene glycol (PEG) chains and 2-ureido-4-pyrimidinone (UPy) moieties through the reaction between isocyanate and carboxyl during the electrode preparation process. In this binder network, PAA could strongly adhere to the Si particles by forming hydrogen bonding with the surface hydroxyl groups. The PEG chains induce the flexibility of the polymer network, while the UPy moieties endow the polymer network with desirable mechanical strength through the formation of reversible and strong quadruple H-bonding cross-linkers. This binder not only can sufficiently accommodate the volume change of Si but can also provide a strong mechanical support to effectively sustain the integrity for the Si anode, consequently enhancing cycle stability and rate performance.

Impact of glycation on physical properties of composite gluten/zein nanofibrous films fabricated by blending electrospinning

In this study, the gluten/zein nanofibrous films were fabricated by blending electrospinning and then glycated with xylose via Maillard reaction. The average fiber diameter of the gluten film decreased from 551 to 343 nm with the increasing ratio of zein, but increased significantly to a range of 717–521 nm after glycation, which induced a higher thermal stability of the nanofibers with an order to disorder transition. The glycated composite films showed the reduced water vapor permeability and improved water stability with a stiffer and more elastic network structure, due to the enhanced intermolecular entanglements and interactions between polymer chains. The results from this work suggested that the composite gluten/zein electrospun films may be glycated via Maillard reaction to obtain desirable physical properties for active food-packaging applications.

Plant protein-based antioxidant Pickering emulsions and high internal phase Pickering emulsions against broad pH range and high ionic strength: Effects of interfacial rheology and microstructure

The present work aimed to explore the stability mechanism of Pickering emulsions (PEs) and high internal phase PEs (HIPPEs) to resist environmental stresses (i.e., pH and ionic strength) via altering the interfacial rheology and microstructure. The storage, centrifugal, oxidative stabilities and interfacial properties of PEs and HIPPEs stabilized by pea protein isolate-high pectin-epigallocatechin gallate (PPI-HMP-EGCG) complex were investigated. The compact and dense viscoelastic interfacial layers, appropriate gel-like elastic network structure and apparent viscosity allowed PEs and HIPPEs to have excellent long-term storage stability, the best centrifugal and oxidative stabilities at pH 3.5 and 0 mmol/L NaCl. As PEs and HIPPEs at neutral and alkaline conditions, the centrifugal and oxidative stabilities of PEs and HIPPEs reduced, which was ascribed to the insufficient number of complexes, leading to the formation of the weak interfacial layer and the decrease of apparent viscosity and viscoelasticity. As NaCl concentration increased to 1000 mmol/L, the oil droplets were not completely surrounded by the interfacial layer with weak viscoelastic response, which resulted in the reduction of centrifugal and oxidative stabilities. These findings are useful to broaden the application of antioxidant PEs and HIPPEs in the food industry under a wide range of pH and ionic strengths.

Reaction mechanism and rheological properties of waste cooking oil pre-desulfurized crumb tire rubber/SBS composite modified asphalt

Waste cooking oil (WCO) is proved to be effective in desulfurization of crumb tire rubber (CTR), which can be considered as a sustainable desulfurization technology and an alternative way to solve the poor storage stability of asphalt rubber. However, WCO pre-desulfurized CTR (ODR) modified asphalt displays a compromised high-temperature performance, leading to a limited application of ODR in asphalt modification. In this study, ODR/styrene–butadiene-styrene (SBS) composite modified asphalt was developed to make up the loss of high-temperature performance. The reaction mechanism of ODR/SBS composite modified asphalts with and without sulfur was investigated via Fourier transform infrared spectroscopy (FTIR), gel permeation chromatograph (GPC) and fluorescence microscope (FM). Rheological tests were conducted to clarify the effects of ODR, SBS and sulfur on the rheological behavior of the modified asphalt. FTIR, GPC and FM results proved that crosslinking reaction occurred during the composite modification of ODR, SBS copolymer and base asphalt in the presence of sulfur with moderate content, forming a continuous and homogeneous microstructure with a significantly increased large molecular weight, which is less prone to produce phase segregation. The ODR composite modified asphalt with 3 wt% SBS and 0.4 wt% sulfur presents the best rutting resistance due to the increase of the elastic network structure and cracking resistance due to the presence of WCO and the released rubber chain. The above composite modified asphalt meets the standard traffic level at 76 °C and the specification at −34 according to the multiple stress creep recovery and bending beam rheometer tests.

Backflow from a model fracture network: an asymptotic investigation

We develop a model for predicting the flow resulting from the relaxation of pre-strained, fluid-filled, elastic network structures. This model may be useful for understanding relaxation processes in various systems, e.g. deformable microfluidic systems or by-products from hydraulic fracturing operations. The analysis is aimed at elucidating features that may provide insight on the rate of fluid drainage from fracturing operations. The model structure is a bifurcating network made of fractures with uniform length and elastic modulus, which allows for general self-similar branching and variation in fracture length and rigidity between fractures along the flow path. A late-time $t^{-1/3}$ power law is attained and the physical behaviour can be classified into four distinct regimes that describe the late-time dynamics based on the location of the bulk of the fluid volume (which shifts away from the outlet as branching is increased) and pressure drop (which shifts away from the outlet as rigidity is increased upstream) along the network. We develop asymptotic solutions for each of the regimes, predicting the late-time flux and evolution of the pressure distribution. The effects of the various parameters on the outlet flux and the network’s drainage efficiency are investigated and show that added branching and a decrease in rigidity upstream tend to increase drainage time.

Recovery of lysozyme from aqueous solution by polyelectrolyte precipitation with sodium alginate

Lysozyme was recovered from its aqueous solution by coprecipitation with sodium alginate. Electrostatic interaction between the two polyelectrolytes could occur between pH 2.0–9.0 and peaked at pH 3.0. The maximum lysozyme recovery of 97.10% was recorded at a mass ratio to sodium alginate of 2:1 and the presence of excessive sodium alginate reduced lysozyme precipitation. Complexation at pH 3.0 conferred the most compact and elastic network structure for the complex, but reduced the thermal stability and caused the greatest structural variation to lysozyme. The complexes separated at pH 4.5 and 6.0 could be dissolved by 1.0 mol/L NaCl, but that at pH 3.0 released only 77% lysozyme and further increase of NaCl concentration could not promote lysozyme liberation. It was concluded that coprecipitation with sodium alginate was potential in recovering lysozyme from its aqueous solutions and the dissociation of resultant complexes should be further enhanced to increase yield.

Designed Elastic Networks: Models of Complex Protein Machinery.

Recently, the design of mechanical networks with protein-inspired responses has become increasingly popular. Here, we review contributions which were motivated by studies of protein dynamics employing coarse-grained elastic network models. First, the concept of evolutionary optimization that we developed to design network structures which execute prescribed tasks is explained. We then review what presumably marks the origin of the idea to design complex functional networks which encode protein-inspired behavior, namely the design of an elastic network structure which emulates the cycles of ATP-powered conformational motion in protein machines. Two recent applications are reviewed. First, the construction of a model molecular motor, whose operation incorporates both the tight coupling power stroke as well as the loose coupling Brownian ratchet mechanism, is discussed. Second, the evolutionary design of network structures which encode optimal long-range communication between remote sites and represent mechanical models of allosteric proteins is presented. We discuss the prospects of designed protein-mimicking elastic networks as model systems to elucidate the design principles and functional signatures underlying the operation of complex protein machinery.

Rheology of fumed silica nanoparticles/partially hydrolyzed polyacrylamide aqueous solutions under small and large amplitude oscillatory shear deformations

Partially hydrolyzed polyacrylamide (HPAM) is one of the most widely used polymers for enhanced oil recovery operations. However, high temperature and high salinity in oil reservoirs restrict its functionality and performance. To alleviate this, incorporating fumed silica nanoparticles (NPs) in HPAM solutions was found to be very effective in harsh oil reservoir conditions to improve the efficiency of polymer flooding. Studying the flow behavior of hybrid polymer and fumed silica NP solutions under real reservoir conditions can be very challenging and hard to achieve due to continuously converging and diverging flow through porous structures. In this regard, rheological analysis of such systems under well-controlled flow histories within the capability of rotational rheometers can be of great importance to fully understand the mechanical response of these hybrid solution systems. In this study, two types of fumed silica NPs with different surface chemistries and two types of HPAM polymers with different molecular weights were dispersed/dissolved in deionized water. Linear viscoelastic properties of the hybrid solution systems were studied based on their step-stress (creep) and small amplitude oscillatory shear responses. As deformation in porous media can be rapid and large, consideration of nonlinear viscoelastic properties can be very crucial. The stress decomposition method and Lissajous–Bowditch curves were used to describe the intercycle and intracycle shear-thickening and strain-stiffening ratios quantitatively and qualitatively. In brief, linear and nonlinear rheology conjugated with thermogravimetric analysis and cryo-scanning electron microscopy imaging enabled us to characterize viscoelastic properties of the hybrid systems and link our observations to microstructural features. Through polymer bridging, the slightly hydrophobic fumed silica NPs (AEROSIL R816) had a unique ability to form interconnected, predominately elastic network structures in contrast to large agglomerated structures formed by highly hydrophilic AEROSIL 300. This has led to observing very different rheological behaviors, regardless of the HPAM polymer molecular weight, below and above a critical fumed silica NPs concentration.

Microporous PDMAEMA‐based stimuli‐responsive hydrogel and its application in drug release

ABSTRACTThe microporous hydrogels (Pn‐Cm gels) composed of poly(dimethylaminoethyl methacrylate) and carboxymethylchitosan were synthesized in situ radical polymerization by using nano γ‐Fe2O3 particles as pore‐agent. The microporous structure formed through eliminating the Fe2O3 particles was designed to achieve a faster response rate and better drug loading effect. Comparing to the neat gels, Pn‐Cm gels exhibit deteriorative mechanical properties with the increased pores, while the gels still keep the elastic network structure which could bear some degree of tensile and compression deformation. Meantime, Pn‐Cm gels show similar temperature and pH double responsiveness with same isoelectric point shrink as that of neat gels, the swelling ability decreases slightly, and the deswelling rate increases with the increase of pores. Moreover, the 5‐fluorouracil was used as a target drug to explore the potential of this gel applied as drug‐release system. For Pn‐Cm gels, the more pores and carboxymethyl chitosan inside the gels are beneficial to the drug loading, all gels show a burst release of drug, being followed by a slow and sustained release with different rate. Comprehensively, the Pn‐Cm gels exhibit a better sustained release effect in the simulated stomach condition (pH = 2.1), the related release mechanism could be interpreted by the superposition of Fickian diffusion. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45326.

Protein-free cress seed (Lepidium sativum) gum: Physicochemical characterization and rheological properties

Protein-free cress seed gum (PFCSG) was obtained by precipitation of crude cress seed gum (CSG) with ethanol followed by treatment with protease. Molecular weight, moisture, ash and uronic acids content decreased after elimination of protein. Elimination of protein improved significantly rheological properties and thermal stability of cress seed gum. Mechanical spectra of the CSG and PFCSG were classified as weak gels and PFCSG showed stronger and more elastic network structure. The gum dispersions exhibited strong shear-thinning behavior which was described satisfactory by the Herschel-Bulkley and Moore models. Protein-free cress seed gum had higher apparent and intrinsic viscosities than the crude gum. CSG indicated lower hysteresis loop area, but degree of structural recovery of the samples showed no significant difference. The main decomposition of PFCSG started above 213°C with two peaks (at 261.72°C and 306.58°C) and initial decomposition temperature of CSG was 190.21°C with one peak at 258.28°C. DSC results coincided with those observed by thermogravimetric analysis. Enzyme treatment lowered the surface activity of CSG.

Purification of cress seed (Lepidium sativum) gum: A comprehensive rheological study

In this paper, the effects of different purification methods (ethanol (sample E), isopropanol (sample I) and ethanol-isopropanol (sample EI)) on intrinsic viscosity, steady and dynamic rheological properties of cress seed gum were investigated. The gum dispersions exhibited viscoelastic properties, the storage modulus (G′) was higher than the loss modulus (G″), and mechanical spectra of the crude and purified cress seed gums were classified as weak gels. The purified samples had stronger and more elastic network structure than the crude gum (CSG) and the gel network got stronger along the series of I, EI and E. All the gum dispersions indicated shear-thinning behavior and the viscosity of the samples followed the order of E > EI > I > CSG. Herschel-Bulkley model was the best model to describe steady shear flow behavior and Arrhenius-type model was also applied to describe the effect of temperature. Crude cress seed gum and EI showed the highest and the lowest activation energy, respectively. The crude and purified gums indicated thixotropic behavior and CSG exhibited the lowest hysteresis loop area and the highest structural recovery. All the samples revealed random coil conformation in dilute regimes, and chain flexibility and intrinsic viscosity enhanced after purification. Intrinsic viscosity of the purified samples increased along the series of I, EI and E.

Preparation of a designed poly(trimethylene carbonate) microvascular network by stereolithography.

Designed flexible and elastic network structures are prepared by stereolithography using a photo-crosslinkable resin based on a poly(trimethylene carbonate) (PTMC) macromer with a molecular weight of 3150 g/mol. Physical properties and the compatibility with human umbilical vein endothelial cells (HUVECs) are evaluated. The hydrophobic networks are found to be flexible and elastic, with an E modulus of 7.9 ± 0.1 MPa, a tensile strength of 3.5 ± 0.1 MPa and an elongation at break of 76.7 ± 0.7%. HUVECs attach and proliferate well on the surfaces of the built structures. A three-dimensional microvascular network is designed to serve as a perfusable scaffold for tissue engineering. In the design, 5 generations of open channels each branch into 4 smaller channels yielding a microvascular region with a high density of capillaries. The overall cross-sectional area through which medium or blood can be perfused remains constant. These structures would ensure efficient nourishment of cells in a large volume of tissue. Built by stereolithography using the PTMC resin, the smallest channels of these structures have square cross-sectional areas, with inner widths of approximately 224 μm and wall thicknesses of approximately 152 μm. The channels are open, allowing water to perfuse the scaffold at 0.279 ± 0.006 mL/s at 80 mmHg and 0.335 ± 0.009 mL/s at 120 mmHg.

Thermo‐Moldable Nanocomposite Hydrogels

The present paper reports an interesting and versatile thermo‐moldable property of poly(N,N‐dimethylacrylamide)‐clay nanocomposite hydrogels (NC gel). The NC gel can be thermo‐pressed and molded to a desired shape at 80 °C, and the shape can be fixed by cooling to 20 °C. Mechanical test and small‐angle X‐ray scattering demonstrate that the molded NC gel still exhibits high strength with an elastic network structure. Viscoelastic measurements show that with increasing the temperature, the equilibrium shear modulus Ge decreases, and the creep and permanent deformation increases obviously, suggesting a decrease in the cross‐linking density. Ge recovers when the gel is cooled down to room temperature, reflecting the recovery of the cross‐linking density. This thermo‐moldable property is attributed to reversible cross‐linking in such NC gels by changing the temperature. This work provides a facile method to deform or pattern the tough NC gels after synthesis.