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Dried abalones are precious products, in which candy abalone is the most treasured one, owing to its unique taste. After rehydration and simmering, the core part tastes extraordinarily tender and viscoelastic, just like a soft candy which may almost melt in mouth. However, the reason for this has yet to be elucidated. The purpose of this study is to research the formation mechanism of the candy-like core in candy abalone. First of all, we characterized the viscoelasticity, microstructure and protein changes of candy abalone during the simmering process. The texture results indicated that the springiness and adhesiveness of candy abalone showed an increase. Scanning and transmission electron microscopy suggested that myofibrillar protein in candy abalone formed a dense three-dimensional network hydrogel structure. Sodium dodecyl sulfate–polyacrylamide gel electrophoresis revealed such a hydrogel structure might be derived from the degradation of the myofibrillar protein during the drying process. Also, we identified degraded peptides mainly stemmed from paramyosin by mass spectrometry. Moreover, molecular dynamics simulation revealed that the hydrogen bonds and hydrophobic interactions are mainly responsible for the self-assembly of peptides during the rehydration and simmering stages. Different from reported protein hydrogels, the rheological and morphological properties of the formed peptide hydrogels in candy abalone have significant changes. In this study, we found that the myofibrillar protein of fresh abalone degraded into peptides during the drying process, which further cross-linked to form a peptide hydrogel during the rehydration and simmering stages, thereby producing a unique viscoelastic candy-like core in candy abalone. [ABSTRACT FROM AUTHOR]

Dual networks formed by entangled polymer chains and wormlike surfactant micelles have attracted increasing interest in their application as thickeners in various fields since they combine the advantages of both polymer- and surfactant-based fluids. In particular, such polymer-surfactant mixtures are of great interest as novel hydraulic fracturing fluids with enhanced properties. In this study, we demonstrated the effect of the chemical composition of an uncharged polymer poly(vinyl alcohol) (PVA) and pH on the rheological properties and structure of its mixtures with a cationic surfactant erucyl bis(hydroxyethyl)methylammonium chloride already exploited in fracturing operations. Using a combination of several complementary techniques (rheometry, cryo-transmission electron microscopy, small-angle neutron scattering, and nuclear magnetic resonance spectroscopy), we showed that a small number of residual acetate groups (2–12.7 mol%) in PVA could significantly reduce the viscosity of the mixed system. This result was attributed to the incorporation of acetate groups in the corona of the micellar aggregates, decreasing the molecular packing parameter and thereby inducing the shortening of worm-like micelles. When these groups are removed by hydrolysis at a pH higher than 7, viscosity increases by five orders of magnitude due to the growth of worm-like micelles in length. The findings of this study create pathways for the development of dual semi-interpenetrating polymer-micellar networks, which are highly desired by the petroleum industry. [ABSTRACT FROM AUTHOR]

This paper analyzes the effect of crosslinking reactions on a thermoset polymer's viscoelastic properties. In particular, a numerical model to predict the evolution of epoxy's mechanical properties during the curing process is proposed and implemented in an Ansys APDL environment. A linear viscoelastic behavior is assumed, and the scaling of viscoelastic properties in terms of the temperature and degree of conversion is modeled using a modified version of the TNM (Tool–Narayanaswamy–Mohynian) model. The effects of the degree of conversion and structural relaxation on epoxy's relaxation times are simultaneously examined for the first time. This formulation is based on the thermo-rheological and chemo-rheological simplicities hypothesis and can predict the evolution of epoxy's relaxation phenomena. The thermal–kinetic reactions of curing are implemented in a homemade routine written in APDL language, and the structural module of Ansys is used to predict the polymer's creep and stress relaxation curves at different temperatures and degrees of conversion. [ABSTRACT FROM AUTHOR]

In the finite element analysis of asphalt concrete (AC), it is nowadays common to incorporate the information from the underlying scales to study the overall response of this material. Heterogeneity observed at the asphalt mixture scale is analyzed in this paper. Reliable finite element analysis (FEA) of asphalt concrete comprises a set of complex issues. The two main aspects of the asphalt concrete FEA discussed in this study are: (1) digital reconstruction of the asphalt pavement microstructure using processing of the high-quality images; and (2) FEA of the asphalt concrete idealized samples accounting for the viscoelastic material model. Reconstruction of the asphalt concrete microstructure is performed using a sequence of image processing operations (binarization, removing holes, filtering, segmentation and boundaries detection). Geometry of the inclusions (aggregate) are additionally simplified in a controlled mode to reduce the numerical cost of the analysis. As is demonstrated in the study, the introduced geometry simplifications are justified. Computational cost reduction exceeds of several orders of magnitude additional modeling error occurring due to the applied simplification technique. Viscoelastic finite element analysis of the AC identified microstructure is performed using the Burgers material model. The analysis algorithm is briefly described with a particular focus on the computational efficiency aspects. In order to illustrate the proposed approach, a set of 2D problems is solved. Numerical results confirm both the effectiveness of the self-developed code and the applicability of the Burgers model to the analyzed class of AC analysis problems. Further research directions are also described to highlight the potential benefits of the developed approach to numerical modeling of asphalt concrete. [ABSTRACT FROM AUTHOR]

The viscoelasticity of mechanically sensitive tissues such as periodontal ligaments (PDLs) is key in maintaining mechanical homeostasis. Unfortunately, PDLs easily lose viscoelasticity (e.g., stress relaxation) during periodontitis or dental trauma, which disrupt cell–extracellular matrix (ECM) interactions and accelerates tissue damage. Here, Pluronic F127 diacrylate (F127DA) hydrogels with PDL‐matched stress relaxation rates and high elastic moduli are developed. The hydrogel viscoelasticity is modulated without chemical cross‐linking by controlling precursor concentrations. Under cytomechanical loading, F127DA hydrogels with fast relaxation rates significantly improved the fibrogenic differentiation potential of PDL stem cells (PDLSCs), while cells cultured on F127DA hydrogels with various stress relaxation rates exhibited similar fibrogenic differentiation potentials with limited cell spreading and traction forces under static conditions. Mechanically, faster‐relaxing F127DA hydrogels leveraged cytomechanical loading to activate PDLSC mechanotransduction by upregulating integrin–focal adhesion kinase pathway and thus cytoskeletal rearrangement, reinforcing cell–ECM interactions. In vivo experiments confirm that faster‐relaxing F127DA hydrogels significantly promoted PDL repair and reduced abnormal healing (e.g., root resorption and ankyloses) in delayed replantation of avulsed teeth. This study firstly investigated how matrix nonlinear viscoelasticity influences the fibrogenesis of PDLSCs under mechanical stimuli, and it reveals the underlying mechanobiology, which suggests novel strategies for PDL regeneration. [ABSTRACT FROM AUTHOR]

Knowledge of the evolution in the mechanical properties of a curing polymer matrix is of great importance in composite parts or structure fabrication. Conventional rheometry, based on small amplitude oscillatory shear, is limited by long interrogation times. In rapidly evolving materials, time sweeps can provide a meaningful measurement albeit at a single frequency. To overcome this constraint, we utilize a combined frequency- and amplitude-modulated chirped strain waveform in conjunction with a homemade sliding plate piezo-operated rheometer (PZR) and a dual-head commercial rotational rheometer (Anton Paar MCR 702) to probe the linear viscoelasticity of these time-evolving materials. The direct controllability of the PZR, resulting from the absence of any kind of firmware and the microsecond actuator-sensor response renders this device ideal for exploring the advantages of this technique. The high frequency capability allows us to extend the upper limits of the accessible linear viscoelastic spectrum and, most importantly, to shorten the length of the interrogating strain signal (OWCh-PZR) to subsecond scales, while retaining a high time-bandwidth product. This short duration ensures that the mutation number (NMu) is kept sufficiently low, even in fast-curing resins. The method is validated via calibration tests in both instruments, and the corresponding limitations are discussed. As a proof of concept, the technique is applied to a curing vinylester resin. The linear viscoelastic (LVE) spectrum is assessed every 20 s to monitor the rapid evolution in the time and frequency dependence of the complex modulus. Comparison of the chirp implementation, based on parameters such as duration of the experiment, sampling frequency, and frequency range, in a commercial rotational rheometer with the PZR provides further information on the applicability of this technique and its limitations. Finally, FTIR spectroscopy is utilized to gain insights into the evolution of the chemical network, and the gap dependence of the evolving material properties in these heterogeneous systems is also investigated. [ABSTRACT FROM AUTHOR]

Nonlinear rheology of Pickering emulsions is used to further investigate the nonlinear and unrecoverable transformation of inner structures, which is beyond the linear viscoelastic regime of tiny structural disturbances. Exploring various rheological methods plays a vital role in emulsion applications, such as simulating the macroscopic structural transformation between static and liquidlike flow states, strain overshoot, and regeneration for broken structures. According to our previous studies, cellulose nanofibers (CNFs) Pickering emulsions are a typical system for investigating polymer-based emulsions with the auxiliary surfactant [didodecyldimethylammonium bromide (DDAB)] for enhancing CNF absorption. To further study different rheological properties by varying CNF or DDAB contents, multiple interval thixotropic test, large amplitude oscillatory shear, and concentration-time-dependent superposition are employed to study the linear viscoelasticity and structural transformation of nonlinear range. This research was conducted based on the previous published works [Cui et al., Materials 15, 8285 (2022)] as a further characterization for the same sample series. [ABSTRACT FROM AUTHOR]

We study theoretically the steady viscoelastic flow in confined and symmetric hyperbolic channels considering slip along the walls. Under the lubrication approximation and a variety of constitutive models, a high-order perturbation solution with respect to the Deborah number is calculated. The solution for all the field variables (velocity, pressure, and extra-stress) is found analytically up to eighth order and is used along with proper acceleration techniques to achieve convergence up to order one Deborah number. We reveal that even in the presence of slip, the pressure drop decreases monotonically with increasing the fluid elasticity. We evaluate the influence of slip in terms arising from two different decompositions of the pressure drop obtained with the aid of the total force balance and the mechanical energy balance of the flow system. In contrast to the nonslip Newtonian flow, our analysis also showed that the fluid slip along the walls introduces variations in the strain rate at the midplane with the distance from the inlet. However, these are small, and an effective strain rate can be well-represented using a previously developed formula [Housiadas, K. D., and A. N. Beris, Phys. Fluids 36(2), 021702 (2024)]. We also show that when the solution for the midplane velocity is used in the general formula for the Trouton ratio, instead of the Newtonian lubrication solution, there are no appreciable changes, thus confirming the validity and accuracy of our previously reported results [Housiadas, K. D., and A. N. Beris, J. Rheol. 68(3), 327–339 (2024)]. [ABSTRACT FROM AUTHOR]

We study theoretically the elongational viscosity (or Trouton ratio, in dimensionless form) for steady viscoelastic flows in confined and symmetric hyperbolic tubes considering Navier-type slip along the wall(s). Both the planar and the cylindrical axisymmetric geometrical configurations are addressed. Under the classic lubrication approximation, and for a variety of constitutive models such as Phan-Thien and Tanner, Giesekus, and Finite Extensibility Nonlinear Elastic with the Peterlin approximation models, the same general analytical formula for the Trouton ratio is derived as for the Oldroyd-B model, in terms of the velocity at the midplane/axis of symmetry and the Deborah number only. Assuming that the velocity field is approximated by the Newtonian lubrication profile, based on our previous study in the absence of slip, we show that a constant extensional strain rate can be achieved in the limits of zero or infinite slip. For finite slip, a slight modification of the geometry is required to achieve a constant strain rate. In these cases, the formula for the steady state Trouton ratio reduces to that for transient homogeneous elongation. We also provide analytical formulae for the modification (decrease) for both the extensional strain rate and the Hencky strain achieved in the confined geometries because of introducing wall slip. [ABSTRACT FROM AUTHOR]

We use nonequilibrium atomistic molecular dynamics simulations of unentangled melts of linear and star oligomer chains ( C 25 H 52 ) to study the steady-state viscoelastic response under confinement within nanoscale hematite (α − F e 2 O 3) channels. We report (i) the negative (positive) first (second) normal stress difference and (ii) the presence of viscoelastic tension at low W i. With the aim of uncovering the molecular mechanism of viscoelasticity, we link these effects to bond alignment such that absorbed chains near the surface can carry the elastic force exerted on the walls, which decays as the chains become more aligned in the flow direction. This alignment is observed to be independent of the film thickness but enhanced as the shear rate increases or the surface attraction weakens. [ABSTRACT FROM AUTHOR]

Numerical simulation of the glass molding process and analysis of material viscoelasticity are growing increasingly significant as the research on optical‐device glass molding intensifies. An accurate and efficient analytical algorithm for the shear relaxation modulus in the viscoelasticity characterization of glass was developed in this study. We measured the high‐temperature creep curve, friction coefficient, and elastic modulus of glass (D‐LaF50) according to the requirements for viscoelasticity characterization. The viscoelastic behavior of glass was characterized based on the analytical algorithm and test results. A finite element analysis model was developed to verify the accuracy of the analytical algorithm. The results show that the error of the proposed algorithm's numerical simulation compared to the test results is within 5%. [ABSTRACT FROM AUTHOR]

In this study, a novel, high content technique using a cylindrical acoustic transducer, stroboscopic fast imaging, and homodyne detection to recover the mechanical properties (dynamic shear modulus) of living adherent cells at low ultrasonic frequencies is presented. By analyzing the micro‐oscillations of cells, whole populations are simultaneously mechanotyped with sub‐cellular resolution. The technique can be combined with standard fluorescence imaging allowing to further cross‐correlate biological and mechanical information. The potential of the technique is demonstrated by mechanotyping co‐cultures of different cell types with significantly different mechanical properties. [ABSTRACT FROM AUTHOR]

Inertial effects caused by perturbations of dynamical equilibrium during the flow of soft matter constitute a hallmark of turbulence. Such perturbations are attributable to an imbalance between energy storage and energy dissipation. During the flow of Newtonian fluids, kinetic energy can be both stored and dissipated, while the flow of viscoelastic soft matter systems, such as polymer fluids, induces the accumulation of both kinetic and elastic energies. The accumulation of elastic energy causes local stiffening of stretched polymer chains, which can destabilise the flow. Migrating multicellular systems are hugely complex and are capable of self-regulating their viscoelasticity and mechanical stress generation, as well as controlling their energy storage and energy dissipation. Since the flow perturbation of viscoelastic systems is caused by the inhomogeneous accumulation of elastic energy, rather than of kinetic energy, turbulence can occur at low Reynolds numbers. This theoretical review is focused on clarifying the role of viscoelasticity in the appearance of low-Reynolds turbulence. Three types of system are considered and compared: (1) high-Reynolds turbulent flow of Newtonian fluids, (2) low and moderate-Reynolds flow of polymer solutions, and (3) migration of epithelial collectives, discussed in terms of two model systems. The models considered involve the fusion of two epithelial aggregates, and the free expansion of epithelial monolayers on a substrate matrix. [ABSTRACT FROM AUTHOR]

Developing a viscoelastic model for the cyclic thermomechanical loading of thermosetting polymers is the main goal of this study. The model includes memory for residual thermal stresses and can consider stress accumulation across many loading cycles. By considering stress accumulation, we can improve predictions and understand how thermosetting polymers' stress–strain state changes under cyclic thermomechanical loading. This approach was validated through experimental verification to ensure its applicability in practical engineering scenarios. The experiment showed that the thermosetting polymer can accumulate stress during cycles of heating and mechanical loading during use. The results of the modeling and experiment are compared. The results have led to corrections in the way this model is applied to thermosetting polymers like the epoxy resin in this study. The corrected results matched well with the experimental measurements of stress under cyclic thermomechanical load, with a difference of only 1 to 6%. [ABSTRACT FROM AUTHOR]

Objectives: To provide a comprehensive summary of the different modalities available to measure soft tissue fibrosis after radiotherapy in head and neck cancer patients. Data Sources: PubMed, Scopus, and Web of Sciences. Review Methods: A search was conducted using a list of medical subject headings and terms related to head and neck oncology, radiation fibrosis, and quantitative measurements, including bioimpedance, MRI, and ultrasound. Original research related to quantitative measurement of neck fibrosis post‐radiotherapy was included without time constraints, while reviews, case reports, non‐English texts, and inaccessible studies were excluded. Discrepancies during the review were resolved by discussing with the senior author until consensus was reached. Results: A total of 284 articles were identified and underwent title and abstract screening. Seventeen articles had met our criteria for full‐text review based on relevance, of which nine had met our inclusion criteria. Young's modulus (YM) and viscoelasticity measures have demonstrated efficacy in quantifying neck fibrosis, with fibrotic tissues displaying significantly higher YM values and altered viscoelastic properties such as increased stiffness rate‐sensitivity and prolonged stress‐relaxation post‐radiation. Intravoxel incoherent motion offers detailed insights into tissue changes by assessing the diffusion of water molecules and blood perfusion, thereby differentiating fibrosed from healthy tissues. Shear wave elastography has proven to be an effective technique for quantifying radiation‐induced fibrosis in the head and neck region by measuring shear wave velocity. Conclusion: There are various modalities to measure radiation‐induced fibrosis, each with its unique strengths and limitations. Providers should be aware of these implications and decide on methodologies based on their specific clinical workflow. Level of Evidence: Step 5. [ABSTRACT FROM AUTHOR]

Considerable development has been observed in the area of applying fractional-order rheological models to describe the viscoelastic properties of miscellaneous materials in the last few decades together with the increasingly stronger adoption of fractional calculus. The fractional Maxwell model is the best-known non-integer-order rheological model. A weighted least-square approximation problem of the relaxation modulus by the fractional Maxwell model is considered when only the time measurements of the relaxation modulus corrupted by additive noises are accessible for identification. This study was dedicated to the determination of the model, optimal in the sense of the integral square weighted model quality index, which does not depend on the particular sampling points applied in the stress relaxation experiment. It is proved that even when the real description of the material relaxation modulus is entirely unknown, the optimal fractional Maxwell model parameters can be recovered from the relaxation modulus measurements recorded for sampling time points selected randomly according to respective randomization. The identified model is a strongly consistent estimate of the desired optimal model. The exponential convergence rate is demonstrated both by the stochastic convergence analysis and by the numerical studies. A simple scheme for the optimal model identification is given. Numerical studies are presented for the materials described by the short relaxation times of the unimodal Gauss-like relaxation spectrum and the long relaxation times of the Baumgaertel, Schausberger and Winter spectrum. These studies have shown that the appropriate randomization introduced in the selection of sampling points guarantees that the sequence of the optimal fractional Maxwell model parameters asymptotically converge to parameters independent of these sampling points. The robustness of the identified model to the measurement disturbances was demonstrated by analytical analysis and numerical studies. [ABSTRACT FROM AUTHOR]

• The reflection/transmission of seismoelectric waves propagating through a sandwiched structure are studied. • A new fractional order viscoelastic model with two attenuation peaks at seismic and sonic frequencies is established. • The seismoelectric effects have noticeable influences on EM wave while negligible influences on seismic waves. • The porosity and the viscoelasticity of solid frame have evident influences on both elastic waves and EM waves The seismoelectric waves generated in a fluid-saturated porous interlayer and the reflection/transmission characteristics at the interfaces of sandwiched structure are studied in this paper. Aiming to describe the strong attenuation and dispersion simultaneously at seismic and sonic frequencies, a new fractional viscoelastic model for the solid skeleton is introduced to the Pride's seismoelectric coupling theory. Using the interfacial continuity of stress, displacements, magnetic and electric fields, the reflection/transmission coefficients are determined. The numerical results are provided and shown graphically. The effects of seismoelectric coupling and the viscoelastic characteristics of solid skeleton on the reflection and transmission of seismoelectric waves are mainly studied. It is observed that the thickness, porosity and the viscoelastic characteristics of solid skeleton have evident effects not only on the electromagnetic waves but also on the seismic waves. [ABSTRACT FROM AUTHOR]

The microstructure of wormlike micelles (WLM) directly affects the rheological properties of their solutions. Investigating the structure–property relationships of WLM has long been a popular topic for researchers who have developed theoretical and empirical models to describe their viscoelastic behavior. All these models rely on a collection of characteristic "length" parameters that are often difficult to estimate using relatively simple rheological tests. In particular, the micelle stiffness, as described by the persistence length, can be difficult to measure experimentally, while being very impactful on the bulk rheology of WLM solutions. Here, an array of inorganic salts (NaCl, LiCl, MgCl2, NaBr, NaI, and Na2SO4) have been used to induce wormlike micelle formation in an aqueous solution of the surfactant sodium lauryl ether sulfate. Ion dissociation/association with the surfactant head groups and the hydrogen bond network of the water alters the effective stiffness of the micelles, allowing for an estimation of the stiffness using three different methods: (1) small angle neutron scattering (SANS) measurements, (2) oscillatory rheological measurements, and (3) steady rheological measurements with a thermodynamic packing parameter model. Each of these methods are then compared and shown to be consistent with each other for the micelle solutions tested. The consistency of the results across all the measurements suggests that the approach used in this study, which estimates micelle parameters using steady shear rheology and a thermodynamic model, could provide a simpler and more accessible method for estimating micelle parameters in a wide range of surfactant systems. [ABSTRACT FROM AUTHOR]

In this paper, layered periodic foundations (LPFs) are numerically examined for their responses to longitudinal and transverse modes in the time and frequency domains. Three different unit-cells, i.e., 2-layer, 4-layer, and 6-layer unit-cells, comprising concrete/rubber, concrete/rubber/steel/rubber, and concrete/rubber/steel/rubber/lead/rubber materials, respectively, are taken into account. Also, the viscoelasticity behavior of the rubber is modeled with two factors, i.e., a frequency-independent (FI) loss factor and a linear frequency-dependent (FD) loss factor. Following the extraction of the complex dispersion curves and the identification of the band gaps (BGs), the simulations of wave transmission in the time and frequency domains are performed using the COMSOL software. Subsequent parametric studies evaluate the effects of the rubber viscoelasticity models on the dispersion curves and the wave transmission for the longitudinal and transverse modes. The results show that considering the rubber viscoelasticity enhances the wave attenuation performance. Moreover, the transverse-mode damping is more sensitive to the viscoelasticity model than its longitudinal counterpart. The 6-layer unit-cell LPF exhibits the lowest BG, ranging from 4.8 Hz to 6.5 Hz. [ABSTRACT FROM AUTHOR]

Elastomers are widely used in electronics and electrical devices, either as insulators or transducers. The insulation and actuation performance of elastomers are highly susceptible to their dielectric strength. Among the factors that influence the dielectric strength of elastomers, material viscoelasticity is an important factor that needs further investigation. Since the material viscoelasticity is often characterized by rate-dependent behaviors, we present two different sample configurations to experimentally examine the electrical and mechanical rate dependence of the dielectric strength of VHB 4905 elastomers. At pre-stretch ratio of 4, the improvement of the dielectric strength is about 30% from voltage ramp of 50 V/s to 800 V/s. Particularly, with an in-house biaxial test platform, the effect of the stretching rate on the dielectric strength is examined for the first time. The improvement of the dielectric strength is about 35% from stretching rate of 0.1 mm/s to 5 mm/s. Moreover, a dielectric strength predictor based on configurational stress is adopted to describe the experimental data. According to the predictor, the loading rate affects the dielectric strength of the elastomer mainly by influencing the evolution of the inelastic deformation. [ABSTRACT FROM AUTHOR]

This paper presents a methodology for the design of deployable tube flexures made of ultra-thin carbon fiber composite. The proposed process aims to enhance viscoelastic resilience on recovery time after long-term stowage through the design of cut-out geometries. Viscoelasticity is modeled using an experimentally determined Prony series master curve. Bayesian optimization is employed to determine cut-out shapes based on the recovery time and Hashin failure criteria. Partial dependent plots are implemented to interpret the effect of cut-out formation on deployment performance. These reveal optimal profiles of cut-out shapes to achieve a desired operational performance. The efficiency of the proposed methodology is validated by experiment. • Viscoelastic and failure performance of tube flexures is enhanced via design optimization. • Bayesian optimization permits exploration of a highly non-linear design space. • A design framework of tube flexures for desired stowage and deployment is presented. [ABSTRACT FROM AUTHOR]

Stalk lodging contributes to significant crop yield losses. Therefore, understanding the biomechanical strength and structural rigidity of grain stalks can contribute to improving stalk lodging resistance in crops. From the structural constituents of the stalk, the rind provides the principal structure, supporting cells against tension and bending loads. In this work, the biomechanical and viscoelastic behavior of the rind from the internodes of two sweet sorghum varieties (Della and REDforGREEN (RG)), grown in two different growing seasons, were evaluated by three-point micro-bending tests using a dynamic mechanical analyzer (DMA). In addition, the chemical composition of rinds and the microfibril angle (MFA) of the cell wall were determined using XRD. The results revealed that the biomechanical behavior of Della varieties was stiffer and more resistant to loads than that of RG varieties. Two features of the rind biomechanical properties, flexural modulus (FM) and flexural strength (FS), showed a significant reduction for RG. Particularly, a reduction in FS of 16–37% and in FM of 22–41% were detected for RG1. Changes in the stalks' rind biomechanical properties were attributed to cell wall components. Total lignin and glucan/cellulose contents were positively correlated with the FM and FS of the rind. Subsequently, an increase in the two cell wall components drove an increase in stiffness. Furthermore, the MFA of the rind was also found to influence the rind strength. [ABSTRACT FROM AUTHOR]

This study comprehensively describes the viscoelastic behavior of high-elasticity modified asphalt mixtures under varying strain conditions. The commonly used sigmoidal model, which relies on a single parameter (dynamic modulus) to depict viscoelastic behavior, has limitations. In this research, by utilizing the dynamic modulus master curve and the Kramers–Kronig relationship, master curve models developed for the phase angle, storage modulus, and loss modulus enable a more comprehensive understanding of the materials' viscoelastic response functions. Dynamic modulus tests were conducted on the high-elasticity modified asphalt mixtures using the simple performance tester (SPT) at various temperatures (5°C, 15°C, 25°C, 40°C, and 55°C) and frequencies (0.1, 0.5, 1, 5, 10, 20, and 25 Hz). The results indicate that the master curves of the phase angle, storage modulus, and loss modulus, established using the dynamic modulus master curve and Kramers–Kronig relationship, are well-fitted, demonstrating that the method feasibly can be used to draw the master curves for each viscoelastic parameter. Additionally, mathematical models based on the Kramers–Kronig relationship were developed to explain the correlations among parameters under dynamic loading conditions, and the accuracy of the master curve models for various parameters was validated. This deeper insight into material responses under varying loading conditions and temperatures can help researchers better model and predict the mechanical performance of pavements. [ABSTRACT FROM AUTHOR]

The form and function of biomolecular condensates are intimately linked to their material properties. Here, we integrate microrheology with molecular simulations to dissect the physical determinants of condensate fluid phase dynamics. By quantifying the timescales and energetics of network relaxation in a series of heterotypic viscoelastic condensates, we uncover distinctive roles of sticker motifs, binding energy, and chain length in dictating condensate dynamical properties. We find that the mechanical relaxation times of condensate-spanning networks are determined by both intermolecular interactions and chain length. We demonstrate, however, that the energy barrier for network reconfiguration, termed flow activation energy, is independent of chain length and only varies with the strengths of intermolecular interactions. Biomolecular diffusion in the dense phase depends on a complex interplay between viscoelasticity and flow activation energy. Our results illuminate distinctive roles of chain length and sequence-specific multivalent interactions underlying the complex material and transport properties of biomolecular condensates. [ABSTRACT FROM AUTHOR]

In this study, aiming at the problem of low strength and high creep caused by medium–low modulus flexible resin based on the formulation design idea of high-molecular-weight epoxy resin (E12)-reinforced flexible epoxy-terminated urethane resin (EUR), a flexible epoxy prepreg resin with high strength and low bending creep was prepared to be suitable for hot melt processing technology. Flexible EUR was synthesized by grafting flexible polyurethane segments onto the epoxy side chain by urethane bonding. By adjusting the ratio of E12 and EUR, the effects of different ratios of the two components on the mechanical properties and viscoelasticity of the resin were systematically studied with dicyandiamide as the latent curing system. Research has found that when the E12 content is between 20%wt and 40%wt, the resin system has the best coating viscosity at 65 °C to 85 °C. The molecular weight and the content of aromatic heterocyclic groups of the resin determine the strength and creep behavior of the resin. When the content of E12 in the system is less than 50%wt, modulus and strength increase linearly, but after more than 50%wt E12 content, the modulus is almost unchanged and the strength begins to decrease. By increasing the content of E12 in the resin, the creep behavior of the resin is greatly reduced. When the content of E12 increases to 50%wt, the bending creep is the lowest. [ABSTRACT FROM AUTHOR]

[Display omitted] Hetero-aggregation of oppositely charged colloidal particles with controlled architectural and interactional asymmetry allows modifying gel nanostructure and properties. We hypothesize the relative size ratio between cationic nanospheres and varied-size anionic two-dimensional nanoclays will influence the gel formation mechanisms and resulting rheological performance. Hybrid colloidal gels formed via hetero-aggregation of cationic gelatin nanospheres (∼400 nm diameter) and five types of nanoclays with similar 1 nm thickness but different lateral sizes ranging from ∼ 30 nm to ∼ 3000 nm. Structure-property relationships were elucidated using a suite of techniques. Microscopy and scattering probed gel nanostructure and particle configuration. Rheology quantified linear and non-linear viscoelastic properties and yielding behavior. Birefringence and polarized imaging assessed size-dependent nanoclay alignment during shear flow. Nanoclay size ratio relative to nanospheres affected the gelation process, network structure, elasticity, yielding, and shear response. Gels with comparably sized components showed maximum elasticity, while yield stress depended on nanoclay rotational mobility. Shear-induced nanoclay alignment was quantified by birefringence, which is more pronounced for larger nanoclay. Varying nanoclay size and interactions with nanospheres controlled dispersion, aggregation, and nematic ordering. These findings indicate that architectural and interactional asymmetry enables more control over gel properties through controlled assembly of anisotropic building blocks. [ABSTRACT FROM AUTHOR]

Development of load-bearing fiber reinforced plastic (hereinafter referred to as FRP) composite structures in civil engineering, exploited under high temperatures, such as industrial chimneys and gas ducts, requires the knowledge of their long-term behavior under constant and cyclic mechanical and temperature loads. Such conditions mean that the viscoelasticity of FRP should be considered along with the thermal aging effect. This research is devoted to the effects of thermal aging on the viscoelastic behavior of polymers. Two sets of experiments were conducted: creep tensile tests and cyclic heating in a constrained state. The Kelvin–Voigt viscoelasticity model was used to determine the rheological parameters of binder from experimental creep curves. Cyclic heating was used to compare the behavior of normal and thermally aged binders and to evaluate the possibility of temperature stress accumulation. Fourier-transform infrared spectroscopy was used for polymer's structural changes investigation. Both tests showed that non-aged glassed polymer (hereinafter referred to as GP) was prone to viscoelastic behavior, while the thermally aged GP lost viscosity and worked almost perfectly elastic. It was assumed that long heat treatment had caused changes in the inner structure of the GP, reducing the number of weak bonds and increasing the number of elastic ones. Therefore, the results show that the designing of FRP structures, exploited under thermomechanical load, requires using the elastic model while taking into account the properties of FRP after long-term heat treatment. [ABSTRACT FROM AUTHOR]

We consider a Cauchy problem for differential equations in a Hilbert space X. The problem is stated in a time interval I, which can be finite or infinite. We use a fixed point argument for history-dependent operators to prove the unique solvability of the problem. Then, we establish convergence criteria for both a general fixed point problem and the corresponding Cauchy problem. These criteria provide the necessary and sufficient conditions on a sequence { u n } , which guarantee its convergence to the solution of the corresponding problem, in the space of both continuous and continuously differentiable functions. We then specify our results in the study of a particular differential equation governed by two nonlinear operators. Finally, we provide an application in viscoelasticity and give a mechanical interpretation of the corresponding convergence result. [ABSTRACT FROM AUTHOR]

[Display omitted] • Viscoelastic measurements of nanometer-thickness polymer brush films were achieved. • Gap dependence of viscoelasticity was investigated to elucidate the film's lubricity. • Correlation between friction and viscoelasticity was revealed. A hydrated 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer brush exhibits exceptional lubricity. This lubrication mechanism has traditionally been attributed to either the inherent fluidity of the brush or the water film that forms owing to its hydrophilic nature. Given previous findings that the frictional properties of the MPC polymer brush film show load dependence, we hypothesize that the lubrication mechanism can be elucidated by examining the shear gap (varies owing to the load) dependence of the brush's viscoelastic response. MPC polymer brush films with different thicknesses were prepared. Their viscoelastic responses were evaluated across different shear gap widths, and the frictional properties were subsequently compared across states with distinct viscoelastic behaviors. The observed shear viscoelasticity demonstrated a clear gap dependence that correlated with frictional attributes. Our data suggests that the lubrication mechanism shifts based on the shear gap. Specifically, two states exhibited low coefficients of friction: one where the osmotic pressure supports the load while allowing flexible deformation of the brush film, and the other where the brush film undergoes compression and transitions to a fully elastic state. [ABSTRACT FROM AUTHOR]

Composites of poly(vinyl alcohol) (PVA) in the shape of braids, in combination with crystals of hydroxyapatite (HAp), were analyzed to perceive the influence of this bioceramic on both the quasi-static and viscoelastic behavior under tensile loading. Analyses involving energy-dispersive X-ray spectroscopy (EDS) and scanning electron microscopy (SEM) allowed us to conclude that the production of a homogeneous layer of HAp on the braiding surface and the calcium/phosphate atomic ratio were comparable to those of natural bone. The maximum degradation temperature established by thermogravimetric analysis (TGA) showed a modest decrease with the addition of HAp. By adding HAp to PVA braids, an increase in the glass transition temperature (Tg) is noticed, as demonstrated by dynamic mechanical analysis (DMA) and differential thermal analysis (DTA). The PVA/HAp composite braids' peaks were validated by Fourier transform infrared (FTIR) spectroscopy to be in good agreement with common PVA and HAp patterns. PVA/HAp braids, a solution often used in the textile industry, showed superior overall mechanical characteristics in monotonic tensile tests. Creep and relaxation testing showed that adding HAp to the eight and six-braided yarn architectures was beneficial. By exhibiting good mechanical performance and most likely increased biological qualities that accompany conventional care for bone applications in the fracture healing field, particularly multifragmentary ones, these arrangements can be applied as a fibrous fixation system. [ABSTRACT FROM AUTHOR]

This paper aims to incorporate the fractional derivative viscoelastic model into a finite element analysis. Firstly, based on the constitutive equation of the fractional derivative three-parameter solid model (FTS), the constitutive equation is discretized by using the Grünwald–Letnikov definition of the fractional derivative, and the stress increment and strain increment relationship and Jacobian matrix are obtained by using the difference method. Subsequently, we degrade the model to establish stress increment and strain increment relationships and Jacobian matrices for the fractional derivative Kelvin model (FK) and fractional derivative Maxwell model (FM). Finally, we further degrade the fractional derivative viscoelastic model to derive stress increment and strain increment relationships and Jacobian matrices for a three-component solid model and Kelvin and Maxwell models. Based on these developments, a UMAT subroutine is implemented in ABAQUS 6.14 finite element software. Three different loading modes, including static load, dynamic load, and mobile load, are analyzed and calculated. The calculations primarily involve a convergence analysis, verification of numerical solutions, and comparative analysis of responses among different viscoelastic models. [ABSTRACT FROM AUTHOR]

Mesenchymal stromal cells (MSCs) showcase remarkable immunoregulatory capabilities in vitro, positioning them as promising candidates for cellular therapeutics. However, the process of administering MSCs and the dynamic in vivo environment may impact the cell–cell and cell–matrix interactions of MSCs, consequently influencing their survival, engraftment, and their immunomodulatory efficacy. Addressing these concerns, hydrogel encapsulation emerges as a promising solution to enhance the therapeutic effectiveness of MSCs in vivo. Hydrogel, a highly flexible crosslinked hydrophilic polymer with a substantial water content, serves as a versatile platform for MSC encapsulation. Demonstrating improved engraftment and heightened immunomodulatory functions in vivo, MSCs encapsulated by hydrogel are at the forefront of advancing therapeutic outcomes. This review delves into current advancements in the field, with a focus on tuning various hydrogel parameters to elucidate mechanistic insights and elevate functional outcomes. Explored parameters encompass hydrogel composition, involving monomer type, functional modification, and co-encapsulation, along with biomechanical and physical properties like stiffness, viscoelasticity, topology, and porosity. The impact of these parameters on MSC behaviors and immunomodulatory functions is examined. Additionally, we discuss potential future research directions, aiming to kindle sustained interest in the exploration of hydrogel-encapsulated MSCs in the realm of immunomodulation. [ABSTRACT FROM AUTHOR]

The respiratory mucus, a viscoelastic gel, effectuates a primary line of the airway defense when operated by the mucociliary clearance. In chronic respiratory diseases (CRDs), such as asthma, chronic obstructive pulmonary disease (COPD), and cystic fibrosis (CF), the mucus is overproduced and its solid content augments, changing its structure and viscoelastic properties and determining a derangement of essential defense mechanisms against opportunistic microbial (virus and bacteria) pathogens. This ensues in damaging of the airways, leading to a vicious cycle of obstruction and infection responsible for the harsh clinical evolution of these CRDs. Here, we review the essential features of normal and pathological mucus (i.e., sputum in CF, COPD, and asthma), i.e., mucin content, structure (mesh size), micro/macro-rheology, pH, and osmotic pressure, ending with the awareness that sputum biomarkers (mucins, inflammatory proteins and peptides, and metabolites) might serve to indicate acute exacerbation and response to therapies. There are some indications that old and novel treatments may change the structure, viscoelastic properties, and biomarker content of sputum; however, a wealth of work is still needed to embrace these measures as correlates of disease severity in association with (or even as substitutes of) pulmonary functional tests. [ABSTRACT FROM AUTHOR]

Coilable booms made of thin-ply composites provide mass and volume efficiency for deploying large structures in space. The recovered shape of the booms after being stowed in the coiled configuration is critical to the deployed stiffness and shape precision of the spacecraft, but is heavily influenced by the viscoelasticity of the polymer composites. A numerical study of coiling, stowing, uncoiling and shape recovery of a viscoelastic thin-ply composite coilable boom is presented in this paper. The formulation of two micromechanics-based viscoelastic shell models and their numerical implementation in structural simulations are presented. The shape recovery of a composite boom coiled for two years, replicating the typical timeline for deployable structures used in solar sail missions, has been simulated. The demonstrated modeling and simulation capability is useful for designing deployable spacecraft structures. • Ply homogenization computes viscoelastic stiffness faster than laminate homogenization. • Ply homogenization has comparable accuracy to laminate homogenization. • Composite deployable booms for solar sails have minimal distortions after stowage. [ABSTRACT FROM AUTHOR]

A viscoelastic Timoshenko micro-beam is investigated using micropolar viscoelasticity theory. The governing equations are derived by applying the principle of virtual displacements, and can be used in a variety of problems. The equations are then reduced to the special case of a homogeneous uniform beam and solved for quasi-static elastic and viscoelastic cases. The viscoelastic material is modeled via standard linear solid model. For the elastic case, a closed-form solution is reached, but for the viscoelastic case, the inverse Laplace transform is calculated numerically by utilizing De Hoog's algorithm. It is shown that the proposed model can capture the size effects, and converges to the classical Timoshenko beam if the beam is thick enough. The model also converges to the micropolar Euler-Bernoulli model if the thickness of the beam is small. The role of distributed couple stress is also investigated in this paper. The results indicate that in a cantilever beam, the distributed couple stress has a high influence on the deflection of the beam, micro-rotation, stress components and couple stress. However, in a beam resting on three supports, it only affects the micro-rotation and the shear stress component in transverse direction (σ x z). Further investigation shows an extremum in some of the results over time, illustrating the importance of taking viscoelastic behaviour into account. [ABSTRACT FROM AUTHOR]

Objective: Age‐related changes in the fiber structure around adipocytes were investigated via scanning electron microscopy (SEM) of excised skin tissues. In addition, the viscoelasticity of the subcutaneous fat layer was evaluated via elastography, and the association between the fiber structure and the viscoelastic properties was assessed. Methods: Skin tissues excised from the facial cheek area were used. Then, SEM images of these tissues were obtained. The thickness and quantity of the fibers around adipocytes were assessed using a 5‐point scale. The score was used to grade 18 tissue samples. Moreover, the viscoelasticity of the subcutaneous fat layer in the same samples was evaluated via ultrasound elastography. Results: Based on the SEM image score, an association was observed between the fiber status score and age, thereby indicating a tendency toward age‐related fibrosis. Fiber structures with high scores, which indicate fibrosis, had a significantly lower viscoelasticity based on ultrasound elastography. Conclusion: The thickness and quantity of fibrous structures around adipocytes in the subcutaneous fat layer increase with age, and these changes can be associated with decreased viscoelasticity in the subcutaneous fat layer. [ABSTRACT FROM AUTHOR]

The 2-methacryloyloxyethyl phosphorylcholine (MPC) polymers are mimetic to phospholipids, being widely used as biocompatible polymers. In our previous study, MPC polymer hydrogels proved more effective for optical tissue clearing compared to acrylamide (AAm) polymer hydrogels. In the present study, 2-acryloyloxyethyl phosphorylcholine (APC) was synthesized and employed to create hydrogels for a comparative analysis with methacrylic MPC-based hydrogels. APC, an acrylic monomer, was copolymerized with AAm in a similar reactivity. In contrast, MPC, as a methacrylic monomer, demonstrated higher copolymerization reactivity than AAm, leading to a spontaneously delayed two-step polymerization behavior. This suggests that the polymer sequences and network structures became heterogeneous when both methacrylic and acrylic monomers, as well as crosslinkers, were present in the copolymerization system. The molecular weight of the APC polymers was considerably smaller than that of the MPC polymers due to the formation of mid-chain radicals and subsequent β-scission during polymerization. The swelling ratios in water and strain sweep profiles of hydrogels prepared using acrylic and methacrylic compounds differed from those of hydrogels prepared using only acrylic compounds. This implies that copolymerization reactivity influences the polymer network structures and crosslinking density in addition to the copolymer composition. APC-based hydrogels are effective for the optical clearing of tumor tissues and are applicable to both passive and electrophoretic methods. [ABSTRACT FROM AUTHOR]

Alkaline sodium hydroxide/sodium silicate-activating high-purity metakaolin geopolymerization is described in terms of metakaolin deconstruction in tetrahedral hydrate silicate [O[Si(OH)3]]− and aluminate [Al(OH)4]− ionic precursors followed by their reassembling in linear and branched sialates monomers that randomly copolymerize into an irregular crosslinked aluminosilicate network. The novelty of the approach resides in the concurrent thermo-calorimetric (differential scanning calorimetry, DSC) and rheological (dynamic mechanical analysis, DMA) characterizations of the liquid slurry during the transformation into a gel and a structural glassy solid. Tests were run either in temperature scan (1 °C/min) or isothermal (20 °C, 30 °C, 40 °C) cure conditions. A Gaussian functions deconvolution method has been applied to the DSC multi-peak thermograms to separate the kinetic contributions of the oligomer's concurrent reactions. DSC thermograms of all tested materials are well-fitted by a combination of three overlapping Gaussian curves that are associated with the initial linear low-molecular-weight (Mw) oligomers (P1) formation, oligomers branching into alumina-rich and silica-rich gels (P2), and inter- and intra-molecular crosslinking (P3). The loss factor has been used to define viscoelastic behavioral zones for each DMA rheo-thermogram operated in the same DSC thermal conditions. Macromolecular evolution and viscoelastic properties have been obtained by pairing the deconvoluted DSC thermograms with the viscoelastic behavioral zones of the DMA rheo-thermograms. Two main chemorheological behaviors have been identified relative to pre- and post-gelation separation of the viscoelastic liquid from the viscoelastic solid. Each comprises three behavioral zones, accounting for the concurrently occurring linear and branching oligomerization, aluminate-rich and silica-rich gel nucleations, crosslinking, and vitrification. A "rubbery plateau" in the loss factor path, observed for all the testing conditions, identifies a large behavioral transition zone dividing the incipient gelling liquid slurry from the material hard setting and vitrification. [ABSTRACT FROM AUTHOR]

Viscous slickwater has a higher viscosity and better sand-carrying ability than conventional slickwater at the same concentration. At a concentration of 0.4 wt.%, the viscosity of the viscous slickwater is 4.7 times that of the conventional slickwater. It is generally believed that viscosity is one of the main influencing factors on the sand-carrying ability of the fluid. However, this study has shown that the good sand-carrying ability of the viscous slickwater is more attributed to its viscoelasticity. Through rheology and sand-carrying tests, it has been found that the viscoelastic properties vary when fluids have the same viscosity; this then leads to a significant difference in the settling rate of sand and the sand-carrying threshold of the fluid in a fracture at a certain flow rate. The routine method of characterizing the viscoelastic property of the slickwater was to observe the cross point of the elastic modulus (G′) and viscous modulus (G″) curves. The smaller the frequency of the cross point, the better the viscoelastic property of the fluid. However, it has been found in experiments that even when the cross point is the same, there is still a significant difference in the sand-carrying ability of fluids. Therefore, sand-carrying experiments are conducted under a similar cross point and different magnitudes of modulus, of which the results indicate that as the elastic modulus increases, the settling rate of sand decreases. The flow rate threshold occurring as sand settles obtained from laboratory experiments is compared with the field condition during hydraulic fracturing. From laboratory experiments, the threshold of inner-fracture flow rate that prevents the sand settling is found to be 8.02 m/min for 0.6 wt.% viscous slickwater with a sand ratio of 30%. In the field operation, the operation conditions meet the sand-carrying threshold obtained from laboratory experiments. Observations from the field test confirm the applicability of the threshold plot proposed according to laboratory measurements, which can provide guidance for optimizing the fracturing scheme in the field. [ABSTRACT FROM AUTHOR]

Elastomers, as a typical category of soft dielectrics, have shown great potential for developing stretchable electronics and soft transducers. However, the performance of dielectric elastomers (DEs) is susceptible to the dielectric permittivity of the material, whether as insulators or actuators. On the other hand, experiments suggest that the material viscoelasticity significantly influences the dielectric permittivity of DEs. Based on the theory of finite-deformation viscoelasticity, this work adopts the Brillouin function to develop a modeling framework to examine the effect of material viscoelasticity on the dielectric permittivity for the first time. A comparison of the data fitting results between the models with and without consideration of the material viscoelasticity is presented. Simulation results also reveal that the viscous network of the elastomer exerts a mitigation effect on the decrease in the dielectric permittivity when the material is deformed. Furthermore, it is found that the loading rate is a key parameter that strongly affects the dielectric permittivity, mainly through the inelastic deformation. [ABSTRACT FROM AUTHOR]

In order to design an involute spline made of PEEK (polyetheretherketone)-based material with better performance and improve the design rules of involute splines, initially, an involute splines design theory for PEEK (polyetheretherketone)-based materials is presented, which combines international standards (ISO 4156, 1. 2. 3, 2005), American standards (ANSI B92.2M. 1989), and traditional empirical formulas. Second, using the involute splines calibration method in international standards as a guide, we developed the involute splines calibration method for PEEK-based materials by estimating the impact of energy consumption caused by viscoelasticity on temperature field calibration. Next, the contact characteristics of the designed spline were analyzed using ABAQUS2022 software to confirm the accuracy and reliability of the design and calibration methods. Finally, finite element simulation was used to analyze the influence of different pressure angles, moduli, combined lengths, and other parameters on the contact characteristics of the spline in order to realize the optimal design of PEEK-based material involute splines, to offer a theoretical foundation and improved design methodology for cylindrical straight-tooth involute splines. [ABSTRACT FROM AUTHOR]

This study investigates the unsteady, magnetohydrodynamic, incompressible, Couette flow of viscoelastic fluid through equidistant upright plates in the presence of permeable media, continuous heat fluxes, heat source, and energy dissipation. The flow is restricted by the flow between two equidistant upright plates, one moving and the other at rest, and the formation of free convection due to a fixed wall at a time-dependent temperature, while heat flow is constant on the wall moving upwards in its plane. The problem is solved analytically, and the expression for velocity and temperature are derived. The effect of numerous physical parameters on the flow is discussed. The local skin friction is also represented graphically, and the Nusselt number is given in the table. [ABSTRACT FROM AUTHOR]

The use of simple bar elements in nonlinear structural finite element formulations has the academic advantage of uncoupling element technology issues from the structural phenomena to be observed. In this work, we present a finite element setting for the formulation of different nonlinear material models applied to the transient analysis of trusses. While nonlinear elasticity is considered by studying a Hooke-like linear relationship between different pairs of nonlinear measures of stress and strain, hyperelasticity is formulated using Ogden's model. Viscoelasticity is introduced using a generalized Kelvin rheological model to account for strain rate effects. The finite kinematics is set in a corotational total Lagrangian description where the virtual work is described using the Second Piola-Kirchhoff and the Green Lagrange measures. Although the derivation is omitted, the consistent tangent moduli are given for all these cases. Numerical problems involving simultaneously different truss models are studied and made available as benchmarks since little comparative data is found in literature. [ABSTRACT FROM AUTHOR]

The aim of this research was to experimentally analyse the possibility of using a rubber hose placed inside a pipeline to mitigate the water hammer phenomenon. The experiments were conducted using a steel pipeline with an inner diameter of 53 mm and an EPDM rubber hose with a diameter of 6 mm. Hydraulic transients were induced by a rapid closure of the valve located at the downstream end of the pipeline system. In order to analyse the influence of steady-state flow conditions on the maximum pressure increase, measurements were carried out for different values of initial pressure and discharge. The experimental results indicate that placing a rubber hose inside a pipeline can substantially attenuate valve-induced pressure oscillations. It was observed that the initial pressure has a significant influence on the capacity of the rubber hose to dampen the water hammer phenomenon. Comparative numerical calculations were performed using the Brunone-Vitkovský instant acceleration-based model of unsteady friction. It was demonstrated that this approach does not allow satisfactory reproduction of the observed pressure oscillations due to the viscoelastic properties of the EPDM hose used in the tests. [ABSTRACT FROM AUTHOR]

Third-degree burn injuries pose a significant health threat. Safer, easier-to-use, and more effective techniques are urgently needed for their treatment. We hypothesized that covalently bonded conjugates of fatty acids and tripeptides can form wound-compatible hydrogels that can accelerate healing. We first designed conjugated structures as fatty acid–aminoacid1–amonoacid2–aspartate amphiphiles (Cn acid–AA1–AA2–D), which were potentially capable of self-assembling into hydrogels according to the structure and properties of each moiety. We then generated 14 novel conjugates based on this design by using two Fmoc/tBu solid-phase peptide synthesis techniques; we verified their structures and purities through liquid chromatography with tandem mass spectrometry and nuclear magnetic resonance spectroscopy. Of them, 13 conjugates formed hydrogels at low concentrations (≥0.25% w/v), but C8 acid-ILD-NH2 showed the best hydrogelation and was investigated further. Scanning electron microscopy revealed that C8 acid-ILD-NH2 formed fibrous network structures and rapidly formed hydrogels that were stable in phosphate-buffered saline (pH 2–8, 37 °C), a typical pathophysiological condition. Injection and rheological studies revealed that the hydrogels manifested important wound treatment properties, including injectability, shear thinning, rapid re-gelation, and wound-compatible mechanics (e.g., moduli G″ and G′, ~0.5–15 kPa). The C8 acid-ILD-NH2(2) hydrogel markedly accelerated the healing of third-degree burn wounds on C57BL/6J mice. Taken together, our findings demonstrated the potential of the Cn fatty acid–AA1–AA2–D molecular template to form hydrogels capable of promoting the wound healing of third-degree burns. [ABSTRACT FROM AUTHOR]

A protocol study was designed to examine cutaneous behavior after continuous application of a peloid in the dry mineral residue of Lanjarón-Capuchina natural mineral water. This study aims to analyze the biomechanical behavior of normal skin using various non-invasive bioengineering techniques after the application of this peloid. We determine the effects of its application for 3 months on 38 healthy volunteers (41.4 ± 5.9 years, range 32–58) without a previous history of skin diseases by courtmetry, sebumetry, pH-metry, reviscometry, and tewametry. It was shown that the production of cutaneous sebum is significantly reduced by 6%, trans epidermal skin loss (TEWL) by 21%, skin fatigue by 30%, elasticity increased by 19%, firmness by 5%, and a skin redensification by 6% was obtained under these experimental conditions. Disparate and non-significant results were obtained concerning pH and viscoelasticity. Continuous skin care with the Lanjarón-Capuchina natural peloid modifies skin behavior, normalizing sebaceous secretion, favoring the biomechanical properties of the skin and the skin barrier function without modifying skin homeostasis. [ABSTRACT FROM AUTHOR]

Polymers are ultra-versatile materials that adapt to a myriad of applications, as they can be designed appropriately for specific needs. The realization of new compounds, however, requires the appropriate experimental characterizations, also from the mechanical point of view, which is typically carried out by analyzing the vibrations of beams, but which still have some unclear aspects, with respect to the well-known dynamics of elastic beams. To address this shortcoming, the paper deals with the theoretical modeling of a viscoelastic beam dynamics and pursues the elucidation of underlying how the flexural vibrations may be affected when an axial pre-load, compressive or tensile, is applied. The analytical model presented is able to shed light on a peculiar behavior, which is strongly related to the frequency-dependent damping induced by viscoelasticity. By considering as an example a real polymer, that is, a synthetic rubber, it is disclosed that an axial pre-load, in certain conditions, may enhance or suppress the oscillatory counterpart of a resonance peak of the beam, depending on both the frequency distribution of the complex modulus and the length of the beam. The analytical model is assessed by a finite element model, and it turns out to be an essential tool for understanding the dynamics of viscoelastic beams, typically exploited to experimentally characterize polymeric materials, and which could vary enormously simply through the application of constraints and ensued pre-loads. [ABSTRACT FROM AUTHOR]

A serious problem in computer simulation of a stress state of polymer structures is to validate the mathematical description of the mechanical properties of materials. The structural model of a viscoelastic material has a number of advantages in describing both the rheology of a material and strain curves of it. In this model, a material is described as a structure consisting of several elements with relatively simple rheological properties. Reproduction of a complex behavior of a material under alternating non-isothermal loading is provided through the interaction of these simple elements. A technique developed in this work for modeling a viscoelastic material is intended for strength calculations of structures made of materials operating under conditions of a long-term repetitive thermomechanical impact using the finite element method. The application of the developed procedure to a polymeric material, polymethyl methacrylate (PMMA), is considered. The results of testing this material under uniaxial compression at a constant temperature are presented. The methodology and results of identification of the developed structural model using a specialized software code are described. Formulas are obtained for the approximation of the deformation characteristics of the material at a constant strain rate and for the time dependence of the deformation of the material during its holding at a constant stress level. Approximation is an important stage in the validation of the material model, which facilitates the systematization of the initial experimental data and their further mathematical processing. The best approximation of the deformation characteristics of a viscoelastic material is provided by a hyperbolic tangent function, whereas a logarithmic function provides the best results for the deformation upon holding. Further construction of the structural model was performed by selecting sequential parameters of bilinear rheological functions of the separate elements of the model and by iterative refinement of these parameters. The simulation results are compared with the experiments performed at different strain rates and with holding at different stress levels. In this work, the results of the initial stage of the performed experimental and theoretical studies are presented. [ABSTRACT FROM AUTHOR]

The lumbopelvic muscle mechanical properties (MMPs) are clinically relevant, but their dependence on sex remains unknown. Therefore, this study aimed to identify if lumbopelvic MMPs depend on the sex in a young adult population. Thirty-five healthy nulliparous women and 35 healthy men were analyzed (age range: 18–50). Lumbopelvic MMPs, that is, tone, stiffness, elasticity, relaxation and creep, assessed with MyotonPRO®, and pelvic floor (PF) health questionnaires were compared between-sexes. Intra-group correlations between sociodemographic and clinical data, and MMPs were also determined. The MMPs of PF were different between healthy non-climacteric adults of both sexes, with women showing higher values of tone and stiffness and lower values of elasticity and viscoelastic properties than men (in all cases, p < 0.03). At lumbar level, tone and stiffness were higher for men at both sides (in all cases, p < 0.04), and relaxation was lower at left side (p = 0.02). The MMPs showed few correlations with sociodemographic data within women. However, within males, there were positive correlations for PF stiffness and viscoelastic parameters with age, BMI and function (0.334 < r < 0.591) and, at lumbar level, negative correlations for tone and stiffness (− 0.385 < r < −0.590) and positive correlations for viscoelastic properties (0.564 < r < 0.719), with BMI. This indicated that between-sexes differences of lumbopelvic MMPs depend on the specific location of assessment in healthy non-obese young individuals. Women show higher tone and stiffness and lower elasticity and viscoelasticity than men, at PF level. [ABSTRACT FROM AUTHOR]