Strain Stiffening Research Articles

IMPACT OF WET GLUTEN CONTENT ON NON-LINEAR VISCOELASTIC PROPERTIES OF WHEAT FLOUR DOUGHS

The impact of wet gluten content in wheat flours on viscoelastic responses of the resulting wheat flour doughs under large deformations were studied using the Large Amplitude Oscillatory Shear (LAOS) tests. For this purpose, dough samples of hard red winter (HRW) wheat flour with 29.80.26% wet gluten and soft red winter (SRW) wheat flour with 23.90.15% wet gluten were obtained at the end of the Farinograph tests. Farinograph mixing stability and optimum water absorption capacity were higher for HRW wheat flour. LAOS tests revealed the contribution of gluten content to the resilience of wheat flour dough against the increasing deformations. Higher strain stiffening was found for HRW wheat flour dough with higher gluten content under large deformations with high frequency, resembling the deformations experienced during dough processing steps such as mixing or sheeting. Intracycle shear thinning behaviors of doughs were not affected by the gluten content at each frequency studied.

Oscillatory rheometry for elucidating the influence of non-network biopolymer aggregation on pectin-gelatin composite gels

Gel networks formed from biopolymers have intrigued rheological interest, especially in the food industry. Despite ubiquitous non-network biopolymer aggregation in real gel food systems, its fundamental rheological implications remain less understood. This study addresses this by preparing pectin-gelatin composite gels with dispersed or aggregated biopolymers and comparatively analyzing viscoelastic responses using rheometry. Subtle discrepancies in non-network biopolymer states were revealed through oscillatory shearing at different frequencies and amplitudes. Biopolymer aggregation in the network notably influenced loss tangent frequency dependency, particularly at high frequencies, elevating I3/I1 values and sensitizing the yield point. Non-network biopolymers weakened Payne effects and gel non-linearity. A combination of strain stiffening and shear thinning nonlinear responses characterized prepared gel systems. Aggregation of pectin and gelatin enhanced shear thinning, while strain stiffening was notable in highly aggregated pectin cases. This study enhances understanding of the link between non-network structural complexity and viscoelastic properties in oscillatory rheometry of food gels.

Effect of xanthan gum on physicochemical properties and 3D printability of emulsion-filled starch gels

The effects of xanthan gum (XG) concentration (0, 0.32%, 0.64%, 0.96%, 1.28%) on the rheological properties, microstructure, and 3D printing characteristics of emulsion-filled starch gels containing curcumin (XG-EFGs) were investigated. The results showed that the interaction between starch and XG led to an increase in mechanical strength with increasing XG concentration. The gels exhibited weak strain overshoot in large amplitude oscillatory shear tests, and the Lissajous curve shifted from elastic dominance to viscous dominance in the transition from linear to nonlinear behavior. The nonlinear parameters also demonstrated that the addition of XG led to strain stiffening and shear thinning behavior. Combining the rheological properties and 3D printing results, it was concluded that the addition of XG effectively improved the dimensional accuracy and stability of the printed products. Also, the addition of XG decreased the hardness, springiness, and gumminess of the XG-EFGs, changed the color brightness,and resulted in a superior delivery system for curcumin. This research contributes to the development of 3D printed gel foods fortified with lipophilic nutrients.

Linear and nonlinear viscoelasticity of edible o/w emulsions used as saturated fat replacers

A recent strategy for controlling saturated fat intake consists on the design of vegetable oil-based emulsions. The aim was to characterize the linear and nonlinear viscoelastic properties of o/w emulsions formulated with two types of cellulose: MX (methylcellulose, MC) and F4M (hydroxypropyl methylcellulose, HPMC). The emulsions were characterized by steady flow curves and frequency sweeps in SAOS (Small Amplitude Oscillatory Shear) regime. In order to evaluate linear and non-linear response, strain sweeps were performed from 0.01 to 1000% strain amplitude at different frequencies (0.1, 1 and 5 Hz). Fourier Transform rheology and orthogonal stress decomposition were applied and LAOS (Large Amplitude Oscillatory Shear) parameters (G’M, G’L, ηM’, ηL’, S and T) were analysed. The type of cellulose ether significantly affected both flow behaviour and internal structure of the samples. MX emulsion presented greater consistency at rest and higher gel strength in SAOS regime with a lower frequency dependence than F4M emulsion. However, both emulsions presented similar properties at large deformations, showing shear thinning and strain stiffening behaviour. Nonlinear viscoelastic analysis allows to improve the textural characterization of emulsions, providing complementary useful information for establishing the most suitable formulation in experimental conditions closer to real applications and processes.

Programming and Reprogramming the Viscoelasticity and Magnetic Response of Magnetoactive Thermoplastic Elastomers.

We present a novel type of magnetorheological material that allows one to restructure the magnetic particles inside the finished composite, tuning in situ the viscoelasticity and magnetic response of the material in a wide range using temperature and an applied magnetic field. The polymer medium is an A-g-B bottlebrush graft copolymer with side chains of two types: polydimethylsiloxane and polystyrene. At room temperature, the brush-like architecture provides the tissue mimetic softness and strain stiffening of the elastomeric matrix, which is formed through the aggregation of polystyrene side chains into aggregates that play the role of physical cross-links. The aggregates partially dissociate and the matrix softens at elevated temperatures, allowing for the effective rearrangement of magnetic particles by applying a magnetic field in the desired direction. Magnetoactive thermoplastic elastomers (MATEs) based on A-g-B bottlebrush graft copolymers with different amounts of aggregating side chains filled with different amounts of carbonyl iron microparticles were prepared. The in situ restructuring of magnetic particles in MATEs was shown to significantly alter their viscoelasticity and magnetic response. In particular, the induced anisotropy led to an order-of-magnitude enhancement of the magnetorheological properties of the composites.

Effects of Microstructural Arrangement on the Mechanical Behavior of 3D Printed Polyamide

This study aims to relate the microstructural arrangement, in particular the symmetry materialized by filament sequencing in the fused filament fabrication process, to the mechanical behavior of printed polyamide. Dog-bone structures were printed using various printing temperatures ranging from 250 °C to 280 °C, which were combined with part orientation including vertical, horizontal, and lateral configurations and raster angles (0°, 15°, 30°, and 45°) that represent the in-plane and out-of-plane symmetrical arrangement of the filament. Mechanical testing was conducted on both as-received filaments and printed structures to derive the effects of filament arrangement symmetry and process-generated defects on mechanical loss. In addition, a microstructural analysis using scanning electron microscopy was used to share more light on the filament arrangements and their consequence on the deformation mechanisms with respect to the printing conditions. The results showed that the 3D printed polyamide-based materials exhibited remarkable tensile performance with strain stiffening behavior and large elongation at break due to their particular filament layout. Among the considered printing conditions, the part orientation was found to have the largest influence on the tensile behavior, which modulates the behavior from complete restoration of the filament performance to mechanical loss.

External factors affecting the linear and nonlinear rheological behavior of oleogel-based emulsions

This study reported oleogel-based emulsions (OGEs, W/O) stabilized by carnauba wax. The effects of different external factors (heating temperature, crystallization temperature, and shear application during crystallization) on the microstructure and linear/nonlinear rheological properties of OGEs were investigated. Microstructural observation suggested that the OGEs had a uniform droplet distribution, and the carnauba wax crystals trapped oil in the continuous phase. The gelatinized oil phase allowed the OGEs to have a solid appearance and typical yielding behavior. The small amplitude oscillation shear analysis showed that lower heating temperature, higher crystallization temperature, and suitable shear application resulted in a stronger, more stable, and tighter packed network structure and better resistance to deformation of the OGEs. For nonlinear behavior, the elastic dominant behavior of OGEs transformed into viscous dominant behavior at large strain amplitudes, accompanied by more energy dissipation, strain stiffening, and a transition from shear thickening to shear thinning.

Effect of fiber properties and orientation on the shear rheology and Poynting effect in meat and meat analogues

The development of plant-based meat analogues is an important aspect of the transition towards using more plant proteins. Production of such products with texture (and rheology) adequate for consumer acceptance like meats is a great challenge. However, there is a current lack in quantitative methods to compare whole cut meats and plant-based analogues that also consider its fibrous structures. We tackled this problem by combining non-linear shear rheology and shear-induced normal stress measurements on whole cut meats (beef and chicken) and plant-based fibrous model systems for meat analogues (soy and pea protein isolates combined with wheat gluten). We found different response in the linear viscoelastic regime for different samples, and the non-linear viscoelastic regime provided a deeper understanding into the role of structural components. Meat samples showed rearrangements at small strains and lower energy dissipation, higher intracycle strain stiffening, and a larger normal stress response at large strains than plant-based fibrous products, due to more elastic fibers. The plant-based fibrous products behave more solid-like until a larger strain, but the fibrous structures break down at large deformations resulting in higher energy dissipation, and show a lower normal stress response than meat. We therefore explore the importance of fiber properties and orientation on the nonlinear rheology of fibrous model systems for meat analogues, and provide a robust methodology to quantitatively compare different mechanical responses of meat and plant-based fibrous meat analogues. These results thereby allow comparison and tuning mechanical responses of plant-based meat analogue products towards real meat.

Interplay of fibrinogen αEC globular domains and factor XIIIa cross-linking dictates the extensibility and strain stiffening of fibrin networks

BackgroundFibrinogen is a plasma protein forming the fibrin scaffold of blood clots. Its mechanical properties therefore affect the risk of bleeding as well as thrombosis. There has been much recent interest in the biophysical mechanisms controlling fibrin mechanics; however, the role of molecular heterogeneity of the circulating fibrinogen in determining clot mechanical function remains poorly characterized. ObjectivesBy comparing 2 fibrinogen variants where the only difference is the Aα-chain length, with one variant having a globular domain at its C-terminus, this study aimed to reveal how the molecular structure impacts the structure and mechanics of fibrin networks. MethodsWe characterized the mechanical response to large shear for networks formed from 2 recombinant fibrinogen variants: the most prevalent variant in circulation with a molecular weight of 340 kDa (recombinant human fibrinogen [rFib] 340) and a minor variant with a molecular weight of 420 kDa (rFib420). ResultsWe show that the elastic properties of the 2 variants are identical when fibrin is cross-linked with factor XIIIa but differ strongly in its absence. Uncross-linked rFib420 networks are softer and up to 3-fold more extensible than rFib340 networks. Electron microscopy imaging showed that the 2 variants formed networks with a comparable structure, except at 4 mg/mL, where rFib420 formed denser networks. ConclusionWe propose that the αEC domains of rFib420 increase the extensibility of uncross-linked fibrin networks by promoting protofibril sliding, which is blocked by FXIIIa cross-linking. Our findings can help explain the functional role of different circulating fibrinogen variants in blood clot mechanics and tissue repair.

Ultra Rate‐Dependent Pressure Sensitive Adhesives Enabled by Soft Elasticity of Liquid Crystal Elastomers

AbstractThe fabrication of pressure sensitive adhesives (PSAs) using liquid crystal elastomers (LCEs), which are known for their excellent dissipation properties, is explored in this work. The adhesive properties of the PSAs are evaluated using the 180° peeling test at various conditions. The performance of the LCE adhesives is found to show significant rate and temperature dependence. When the adhesion energy is plotted against the rate, LCE shows an anomalously large power law exponent (n ≈ 1.17) compared to existing PSAs (n ≈ 0.1–0.6). The unusual rate sensitivity is hypothesized to originate from the synergy of soft elasticity and non‐linear viscoelasticity. The adhesive properties at various rates and temperatures are correlated to the results from dynamic mechanical analysis. Moreover, the large strain stiffening behavior of LCE under uniaxial tension reveals the distinctive advantages offered by LCE as adhesives. Time‐temperature superposition is used to obtain a master curve of adhesion energy that spans rates beyond typical experimental limits. The extreme rate dependence and the large strain stiffening of LCE yield a new category of adhesives that possess special properties, such as reversible adhesion and impact resistance, unlike traditional adhesives.

Asymmetry of tensile versus compressive elasticity and permeability contributes to the regulation of exchanges in collagen gels.

The Starling principle describes exchanges between blood and tissues based on the balance of hydrostatic and osmotic flows. However, the permeation properties of the main constituent of tissues, namely, collagen, in response to the stress exerted by blood pressure remain poorly characterized. Here, we develop an instrument to determine the elasticity and permeability of collagen gels under tensile and compressive stress based on measuring the temporal change in pressure in an air cavity sealed at the outlet of a collagen slab. Data analysis with an analytical model reveals a drop in the permeability and enhanced strain stiffening of native collagen gels under compression versus tension, both effects being essentially lost after chemical cross-linking. Furthermore, we report the control of the permeability of native collagen gels using sinusoidal fluid injection, an effect explained by the asymmetric response in tension and compression. We lastly suggest that blood-associated pulsations could contribute to exchanges within tissues.

New insights into the effects of starch-oleic acid-chlorogenic acid interactions on structural formation by hot-extrusion 3D printing: From perspective of nonlinear rheology

Nonlinear rheology can be used to monitor the molecular chain movement of polymer materials under large strain conditions. In this work, we firstly set up large amplitude oscillatory shear (LAOS) conditions simulating the hot-extrusion 3D printing (HE-3DP) process and attempted to match the structural formation of wheat starch (WS) by starch-oleic acid (OA)-chlorogenic acid (CA) interactions during HE-3DP from perspectives of nonlinear rheology. Results showed that when compared with WS system, the b value and zero-strain nonlinearity (Q0) of WS-OA system increased with OA addition, and it exhibited obvious strain hardening and shear thinning behaviors, which were ascribed to that OA interacted with starch to form single helix and V-type crystalline structure through hydrophobic force, and it obstructed the integrality of gel network. For WS-CA system, the b value and Q0 decreased with CA addition and the shear thickening behavior was increased which could be explained that CA interacted with starch chains through hydrogen bonding following the formation of aggregates structure, thus improving the integrity of network structure. Notably, when compared to above two binary systems, the early emergence of strain thickening and the weakening of strain stiffening for WS-OA-CA system declared that CA contributed to inhibiting the aggregation and assembly of the single helix formed by WS-OA interactions. Overall, this study provided important information for the application of nonlinear rheology in the structure evolution of starch system during HE-3DP.

Strain stiffening retards growth instability in residually stressed biological tissues

Soft biological tissues often exhibit notable strain stiffening under increasing stretch, and this can have significant effects on tissue growth and morphological development, such as causing symmetry breaking in growing airways and leading to mucosal folding and airway hyperresponsiveness. To investigate the role of strain stiffening and the multifactorial control in growth and remodeling, we consider a growing tubular structure with strain-stiffening effects caused by increased and tightened collagen. In addition, we employ the nonlinear hyperelastic Gent model and initial stress symmetry theory to include the coupling effects of differential growth and initial residual stress. Results show that for strain stiffening that takes place at higher strain (Jm>21), the maximum critical growth ratio matches that obtained using neo-Hookean model calculations. Meanwhile, for biological tissues that exhibit strain stiffening under moderate strain conditions (0.46<Jm<21), the strain-stiffening effect delays significantly the onset of growth instability. When strain stiffening takes place at very low strains (Jm<0.46), stiff biological tissues can prevent growth instability, resulting in a smooth hyperelastic cylindrical tubular structure, and the epithelial tissue remains stable at all growth stages without forming any unstable morphology. Our results suggest that strain stiffening can induce retardation instability during biological growth and remodeling, but airway remodeling can incorporate this effect by increasing wall stiffness and reducing obstruction. This highlights the importance of considering the impact of strain stiffening on biological growth and remodeling, which can inform the development of effective clinical interventions for chronic inflammatory airway diseases.

Dynamic remodeling of fiber networks with stiff inclusions under compressive loading.

The ability of tissues to sustain and withstand mechanical stress is critical to tissue development and healthy tissue maintenance. The mechanical properties of tissues are typically considered to be dominated by the fibrous extracellular matrix (ECM) component of tissues. Fiber network mechanics can capture certain mechanical features of tissues, such as shear strain stiffening, but is insufficient in describing the compressive response of certain tissues and blood clots that are rich in extracellular matrix. To understand the mechanical response of tissues, we employ a contemporary mechanical model, a fibrous network of fibrin embedded with inert bead inclusions that preserve the volume-conserving constraints of cells in tissues. Combining bulk mechanical rheology and a custom imaging device, we show that the presence of inclusions alters the local dynamic remodeling of the networks undergoing uniaxial compressive strains and demonstrate non-affine correlated motion within a fiber-bead network, predicted to stretch fibers in the network and lead to the ability of the network to stiffen under compression, a key feature of real tissues. These findings have important implications for understanding how local structural properties of cells and ECM fibers impact the bulk mechanical response of real tissues. STATEMENT OF SIGNIFICANCE: To understand why real tissue stiffens under compression, we study a model tissue system which also stiffens: a fibrin network embedded with stiff beads. We design a device that images compression of both fiber and fiber-bead networks. Distinct from previous imaging studies, this setup can dynamically capture network deformation on scales larger than single fibers. From the videos, we see fluid flow and network remodeling are both critical to compression behavior. The fiber-bead network has faster fluid flow, reduced network recovery, and correlated motion during network relaxation. We hypothesize that the beads hinder network relaxation of stretched fibers, thus retaining the applied stress and exhibiting stiffening. Our findings reveal important details for modeling tissue mechanics towards optimizing healthcare.

Comparison of mixing and non-linear viscoelastic properties of carob germ glutelins and wheat glutenin

Carob germ glutelins were compared to wheat glutenin from a rheological standpoint to provide a basis for the possible use of carob germ glutelins as a non-gluten protein in gluten-free dough systems. Molecular weight distributions, mixing and non-linear viscoelastic properties of carob germ glutelins and wheat glutenin were compared, while the impact of mixing on non-linear rheological properties of these protein fractions were evaluated over short (4-min) and long (35-min) mixing times. Development time was 13 min for carob germ glutelins, while reaching 500 BU consistency took 34 min for wheat glutenin, suggesting faster hydration for carob germ glutelins due to their relatively lower molecular weight distribution and more hydrophilic nature. Phase angle values revealed similar linear viscoelastic properties for both proteins after 4-min and 35-min mixing. However, Large Amplitude Oscillatory Shear (LAOS) tests indicated type I non-linear behavior for carob germ glutelins and type III non-linear behavior for wheat glutenin after 35-min mixing at which both proteins had similar consistencies, pointing out to weaker stability for carob germ glutelins when exposed to large deformations. Higher degree of strain stiffening and shear thinning behaviors were found for carob germ glutelins in the non-linear region. Increasing mixing time caused a decrease in the strain stiffening behavior of wheat glutenin under large strain-high frequency deformations, while strain stiffening behavior of carob germ glutelins remained similar. Comparing the mixing and LAOS properties of carob germ glutelins to those of wheat glutenin unraveled the processing needs of dough systems where carob germ glutelins could be used as a non-gluten protein to produce alternative gluten-free baked products with improved quality.

An investigation into the nonlinear rheological behavior of modified asphalt binders using large amplitude oscillatory shear rheology

ABSTRACT Asphalt binders have been studied extensively with respect to their linear viscoelastic properties. From these properties, performance metrics have been derived and used for specification purposes. However, these materials are used in asphalt concrete pavements where they may experience time-dependent loads in the nonlinear regime. In the past, the vast majority of asphalt binders exhibited strong correlations between their linear and nonlinear properties and so despite this mismatch in characterization and the actual use phase domains, a system based on linear properties could be reliably deployed. More recently though, novel binders and additives have been introduced with differing relationships between linear and nonlinear behaviors. As such there is a need to characterize the asphalt binder response under large strains and use specifications that more explicitly account for the binder nonlinearity. Here, an attempt has been made to characterize the nonlinear rheological properties of asphalt binder using large amplitude oscillatory shear. The response of a single terminal blend, crumb rubber modified binder under large strains is analyzed using Lissajous-Bowditch plots while the contribution of higher harmonics is evaluated using Fourier-transform rheology. Finally, the elastic and viscous contributions are obtained using stress decomposition to an orthogonal set of Chebyshev polynomials. It is found that the relative nonlinearity increases with increasing strain and frequency under the tested conditions. The asphalt binder evaluated in this study predominantly exhibits shear thinning and either strain stiffening or softening behavior depending upon the test conditions. The applicability of time-temperature superposition in the nonlinear regime for asphalt binders is also evaluated.

On the strain stiffening and nanofiber orientation of physically crosslinked nanocellulose hydrogels

Nanocellulose hydrogels that consist of physically crosslinked nanofibrous networks with large amounts of interstitial water have many potential applications as structural materials in biomedical engineering. Quantifying the relationship between micro/nanostructures and their mechanical responses can provide some guidelines for the high-performance mechanical design of counterparts. To this end, we develop a modified physically based constitutive model for examining the effects of the micro/nanostructures of a nanofibrous network on the strain stiffening behaviors of nanocellulose hydrogels under stretching. In addition to the configurational entropy of cellulose nanofiber and mixing energy of water molecule, this theoretical model is particularly concerned with the contribution of the potential energy of hydrogen bond in a thermodynamics framework. Increasing the physical crosslinks between cellulose nanofibers or decreasing the content of water molecules in a certain range can enhance the strain stiffening behaviors of nanocellulose hydrogels. Relatively long and thin cellulose nanofibers have increased tensile strengths. The theoretical predictions are in good agreement with the relevant experimental results. We propose a fiber orientation model for quantifying the relationship between the nanofiber orientation degree and mechanical stretching. This model provides a theoretical foundation for fabricating anisotropic nanofibrous hydrogels via cold drawing.

Investigating the physical and quality characteristics and rheology of mayonnaise containing aquafaba as an egg substitute

This paper aimed to examine the effect of using aquafaba in different ratios (25%, 50%, 75%, 100%) as an egg yolk substitute on the physical, structural, and rheological properties of mayonnaise. Large amplitude oscillatory shear analysis (LAOS) parameters (ηL′, ηM′, G'L, G'M, e3, e1, v3, v1) were evaluated to determine the rheological properties of mayonnaise samples. The droplet size of samples significantly increased and the stability of the emulsion decreased after 50% substitution ratio. The density of mayonnaise significantly increased with increased aquafaba substitution. According to Lissajous curves, egg yolk substitution with aquafaba leads to a decrease in stress values. Aquafaba affected the microstructure of samples and decreased the dissipated and stored energies. The LAOS parameters showed that the sample's behavior is strain stiffening and shear thinning in the nonlinear region. Textural parameters decreased with increased ratio of aquafaba. Significant differences were observed for L*, a*, b* and ΔE values.

Ambient Environment Adaptive Elastomer Constructed by Microphase Separation and Segment Complexation of Triblock Copolymers.

Elastomers with environmental adaption have attracted considerable attention for advanced applications in various areas. Here, we fabricate an ambient environment adaptive elastomer by assembling triblock copolymers polystyrene-b-poly(acrylic acid)-b-polystyrene (SAS) and polystyrene-b-poly(ethylene oxide)-b-polystyrene (SES). Owing to the microphase separation of triblock polymers and hydrogen-bonding complexation of their middle segments, the SAS/SES complex presents dichotomy of vitrified hard PS domains and soft PAA/PEO domains, which presents major relaxation transition in the temperature zone 10-30 °C and relative humidity (RH) 40-60%. The SAS/SES elastomer presents quick adaption to the ambient environment change with temperature and humidity coupling. Moreover, after a loading-unloading cycle training, the SAS/SES elastomer exhibits domain orientation, low energy dissipation, high recovery ratio, and distinct strain stiffening compared with the pristine complex. The SAS/SES elastomer has potential to be used as a sensing and adaption component for complicated intelligent systems.

Module-Assembled Elastomer Showing Large Strain Stiffening Capability and High Stretchability.

Elastomers are indispensable materials due to their flexible, stretchable, and elastic nature. However, the polymer network structure constituting an elastomer is generally inhomogeneous, limiting the performance of the material. Here, a highly stretchable elastomer with unprecedented strain-stiffening capability is developed based on a highly homogeneous network structure enabled by a module assembly strategy. The elastomer is synthesized by efficient end-linking of a star-shaped aliphatic polyester precursor with a narrow molecular-weight distribution. The resulting product shows high strength (≈26MPa) and remarkable stretchability (stretch ratio at break ≈1900%), as well as good fatigue resistance and notch insensitivity. Moreover, it shows extraordinary strain-stiffening capability (>2000-fold increase in the apparent stiffness) that exceeds the performance of any existing soft material. These unique properties are due to strain-induced ordering of the polymer chains in a uniformly stretched network, as revealed by in situ X-ray scattering analyses. The utility of this great strain-stiffening capability is demonstrated by realizing a simple variable stiffness actuator for soft robotics.