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Typical extension flow occurs in electrospinning process of Poly(vinylidene fluoride) (PVDF) solutions such that researchers focus on extensional rheological behaviors of PVDF solutions. The extensional viscosity of PVDF solutions is measured to know the fluidic deformation in extension flows. The solutions are prepared by dissolving PVDF powder into N,N-dimethylformamide (DMF) solvent. A homemade extensional viscometric device is used to produce uniaxial extension flows and the feasibility of the viscometric device is verified by applying the glycerol as a test fluid. Experimental results show that PVDF/DMF solutions are extension shinning as well as shear shinning. The Trouton ratio of thinning PVDF/DMF solution is close to three at very low strain rate and then reaches a peak value until it drops to a small value at high strain rate. Furthermore, an exponential model may be used to fit the measured values of uniaxial extensional viscosity at various extension rates, while traditional power-law model is applicable to steady shear viscosity. For 10~14% PVDF/DMF solution, the zero-extension viscosity by fitting reaches 31.88~157.53 Pa·s and the peak Trouton ratio is 4.17~5.16 at applied extension rate of less than 34 s-1. Characteristic relaxation time is λ~100 ms and corresponding critical extension rate is ε˙c~5 s-1. The extensional viscosity of very dilute PVDF/DMF solution at very high extension rate is beyond the limit of our homemade extensional viscometric device. This case needs a higher sensitive tensile gauge and a higher-accelerated motion mechanism for test.

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The incorporation of poly(d-lactide) (PDLA) to form stereocomplex crystallites (SCs) within a poly(l-lactide) (PLLA) matrix is among the most effective strategies in overcoming PLLA's numerous drawbacks. However, high concentrations of PDLA (>3 wt%) are required to improve PLLA's crystallization kinetics and melt strength, which is undesirable owing to PDLA's high cost. In this study, we use chain alignment as a levier to tune stereocomplex superstructure morphology to overcome these limitations. Herein, PLLA/PDLA blends were manufactured using an environmentally friendly and low-cost single step spunbond fibrillation process, yielding microfibers stretched to diameters of 5-20 µm. During this stretching process, PLLA and PDLA chains are aligned along the flow direction. SCs subsequently formed in situ upon heating, dramatically improving crystallization kinetics, melt elasticity, and tensile performance compared with neat PLLA and non-stretched blend analogues, even with low PDLA content (<3 wt%). These improvements were attributed to topological variations in SC superstructures caused by alignment of PLLA and PDLA chains. The application of chain alignment in tuning SC superstructure morphology is ubiquitous in fibrillation processes.

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Knowledge of the mechanical properties of blood vessels and determining appropriate constitutive relations are essential in developing methodologies for accurate prognosis of vascular diseases. We examine the directional variation of the mechanical properties of the porcine thoracic aorta by performing uniaxial extension tests on dumbbell-shaped specimens cut at five different orientations with respect to the circumferential direction of the aorta. Specimens in all the orientations considered exhibit a nonlinear constitutive response that is typical of collagenous soft tissues. Shear strain under uniaxial extension demonstrates clearly discernible anisotropy of the mechanical response of the porcine aorta, and samples oriented at 45[Formula: see text] and 60[Formula: see text] with respect to the circumferential direction show a peculiar crescent-shaped shear strain-nominal stretch response not displayed by axial and circumferential specimens. Failure stress indicates decreasing tensile strength of the porcine aortic wall from the circumferential direction to the longitudinal direction. Furthermore, we determine the material parameters for the four-fiber-family and Gasser-Holzapfel-Ogden models from the mechanical response data of the circumferential and longitudinal specimens. It is shown how the material parameters derived from the uniaxial tests on circumferential and longitudinal specimens are insufficient to characterize the response of off-axis specimens.

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Studying and quantifying the mechanics of blood clots is essential to better diagnosis and prognosis of, as well as therapy for, thromboembolic pathologies such as strokes, heart attacks, and pulmonary embolisms. Unfortunately, mechanically testing blood clots is complicated by their softness and fragility, thus making the use of classic mounting techniques, such as clamping, challenging. This is particularly true for mechanical testing under large deformation. Here, we describe protocols for creating in vitro blood clots and securely mounting these samples on mechanical test equipment. To this end, we line 3D-printed molds with a hook-and-loop fabric that, after coagulation, provides a secure interface between the sample and device mount. In summary, our molding and mounting protocols are ideal for performing large-deformation mechanical testing, with samples that can withstand substantial deformation without delaminating from the apparatus. © 2021 Wiley Periodicals LLC. Basic Protocol 1: Cube-shaped blood clot preparation Basic Protocol 2: Sheet-shaped blood clot preparation.

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Current clinical practice for aneurysmatic interventions is often based on the maximum diameter of the vessel and/or on the growth rate, although rupture can occur at any diameter and growth rate, leading to fatality. For 27 medial samples obtained from 12 non-aneurysmatic (control) and 9 aneurysmatic human descending thoracic aortas we examined: the mechanical responses up to rupture using uniaxial extension tests of circumferential and longitudinal specimens; the structure of these tissues using second-harmonic imaging and histology, in particular, the content proportions of collagen, elastic fibers and smooth muscle cells in the media. It was found that the mean failure stresses were higher in the circumferential directions (Control-C 1474kPa; Aneurysmatic-C 1446kPa), than in the longitudinal directions (Aneurysmatic-L 735kPa; Control-L 579kPa). This trend was the opposite to that observed for the mean collagen fiber directions measured from the loading axis (Control-L > Aneurysmatic-L > Aneurysmatic-C > Control-C), thus suggesting that the trend in the failure stress can in part be attributed to the collagen architecture. The difference in the mean values of the out-of-plane dispersion in the radial/longitudinal plane between the control and aneurysmatic groups was significant. The difference in the mean values of the mean fiber angle from the circumferential direction was also significantly different between the two groups. Most specimens showed delamination zones near the ruptured region in addition to ruptured collagen and elastic fibers. This study provides a basis for further studies on the microstructure and the uniaxial failure properties of (aneurysmatic) arterial walls towards realistic modeling and prediction of tissue failure. STATEMENT OF SIGNIFICANCE: A data set relating uniaxial failure properties to the microstructure of non-aneurysmatic and aneurysmatic human thoracic aortic medias under uniaxial extension tests is presented for the first time. It was found that the mean failure stresses were higher in the circumferential directions, than in the longitudinal directions. The general trend for the failure stresses was Control-C > Aneurysmatic-C > Aneurysmatic-L > Control-L, which was the opposite of that observed for the mean collagen fiber direction relative to the loading axis (Control-L > Aneurysmatic-L > Aneurysmatic-C > Control-C) suggesting that the trend in the failure stress can in part be attributed to the collagen architecture. This study provides a first step towards more realistic modeling and prediction of tissue failure.

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It is known that uniaxially drawn perfluoronated sulfonic-acid ionomers (PFSAs) show diffusion anisotropy because of the aligned water channels along the deformation direction. We apply the uniaxially stretched membranes to vanadium redox flow batteries (VRFBs) to suppress the permeation of active species, vanadium ions through the transverse directions. The aligned water channels render much lower vanadium permeability, resulting in higher Coulombic efficiency (>98%) and longer self-discharge time (>250 h). Similar to vanadium ions, proton conduction through the membranes also decreases as the stretching ratio increases, but the thinned membranes show the enhanced voltage and energy efficiencies over the range of current density, 50-100 mA/cm2. Hydrophilic channel alignment of PFSAs is also beneficial for long-term cycling of VRFBs in terms of capacity retention and cell performances. This simple pretreatment of membranes offers an effective and facile way to overcome high vanadium permeability of PFSAs for VRFBs.

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We present basic experimental data and the theoretical background of a novel technique for fiber spinning from polymer solutions. The principal feature of the advanced process is realization of phase separation with detachment of a solvent, accompanied by the orientation of macromolecules, under the action of high extension rates. This is similar in some respects to dry spinning, though the driving force is not diffusion with subsequent evaporation of a solvent but redistribution of polymer-solvent interactions in favor of polymer-polymer and solvent-solvent ones governed by mechanical stresses. A promise of this approach has been demonstrated by experiments performed with polyacrylonitrile solutions in different solvents and solutions of the rigid-chain aromatic polyamide. We examined mechanotropic fiber spinning in model experiments with stretching jets from a drop of polymer solution in different conditions, and then demonstrated the possibility of realizing this process in the stable long-term continuous mode. During extension, phase separation happens throughout the whole section of a jet, as was confirmed by visual observation. Then a solvent diffuses on a jet surface, forming a liquid shell on the oriented fiber. Instability of this cover due to surface tension leads either to formation of separate solvent drops "seating" on the fiber or to the flow of a solvent down to the Taylor cone. The separate liquid droplets can be easily taken off a fiber. The physics underlying this process is related to the analysis of the influence of macromolecule coil-to-stretched chain transition on the intermolecular interaction.

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Tension pneumothorax, a major preventable cause of battlefield death, often arises from chest trauma and is treated by needle decompression to release trapped air from the pleural cavity. Surgical simulation mannequins are often employed to train medical personnel to perform this procedure properly. Accurate reproduction of the mechanical behavior of the parietal pleura, especially in response to needle penetration, is essential to maximize the fidelity of these surgical simulators. To date, however, the design of pleura-simulating material has been largely empirical and based on subjective practitioner feel rather than on the tissue properties, which have remained unknown. In this study, we performed uniaxial extension tests on samples of cadaveric human parietal pleura. We found that the pleura was highly nonlinear and mildly anisotropic, being roughly twice as stiff in the direction parallel to the ribs vs. perpendicular to the ribs (large-strain modulus = 20.44 vs. 11.49MPa). We also did not find significant correlations for most pleural properties with age or BMI, but it must be recognized that the age range (59 ± 9.5 yrs) and BMI range (31 ± 5.3) of the donors in our study was not what one might expect from combatants, and there could be differences for younger, lighter individuals. We found a significantly higher low-strain modulus in the diabetic donors (0.213 vs. 0.100MPa), consistent with the general tendency of tissue to stiffen in diabetes. The nonlinearity and tensile strength should be considered in material design and selection for future surgical simulators.

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Biphasic calcium phosphate (BCP) bioceramics, the mixture of hydroxyapatite (HA) and beta- tricalcium phosphate (ß-TCP), are widely used as bone repair materials. Optimization of its composition and mixing pattern is crucial for its design and preparation. A series of BCP structures with a HA/ß-TCP mass ratio of 0/100, 30/70, 50/50, 70/30, and 100/0 were constructed and studied with a simulated annealing molecular dynamics method. On the basis of equilibrated BCP structures, their elastic constants and moduli were computed and analyzed. With increasing HA content, the elastic moduli of BCP increase. Under the same mass ratio (50/50), the elastic moduli have no distinct changes for different mixing patterns. Calculations on the uniaxial extension of BCP reveal a sophisticated nonlinear and loading-path dependent behavior. The maximum stress decreases with increasing ß-TCP content and mixing level.

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The characterization of the extensional rheology of polymeric solutions is important in several applications and industrial processes. Filament stretching and capillary breakup rheometers have been developed to characterize the extensional properties of polymeric solutions, mostly for high-viscosity fluids. However, for low concentration polymer solutions, the measurements are difficult using available devices, in terms of the minimum viscosity and relaxation times that can be measured accurately. In addition, when the slow retraction method is used, solvent evaporation can affect the measurements for volatile solvents. In this work, a new setup was tested for filament breakup experiments using the slow retraction method, high-speed imaging techniques, and an immiscible oil bath to reduce solvent evaporation and facilitate particle tracking in the thinning filament. Extensional relaxation times above around 100 µs were measured with the device for dilute and semi-dilute polymer solutions. Particle tracking velocimetry was also used to measure the velocity in the filament and the corresponding elongation rate, and to compare with the values obtained from the measured exponential decay of the filament diameter.

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The skin tissue has been shown to behave like a nonlinear anisotropic material. This study was aimed to employ a constitutive fiber family equation to characterize the nonlinear anisotropic mechanical behavior of the rat and mice skin tissues in different anatomical locations, including the abdomen and back, using histostructural and uniaxial data. The rat and mice skin tissues were excised from the animals' body and then the histological analyses were performed on each skin type to determine the mean fiber orientation angle. Afterward, the preconditioned skin tissues were subjected to a series of quasi-static axial and circumferential loads until the incidence of failure. The crucial role of fiber orientation was explicitly added into a proposed strain energy density function. The material coefficients were determined using the constrained nonlinear optimization method based on the axial and circumferential extension data of the rat and mice samples at different anatomical locations. The material coefficients of the skins were given with R(2) ≥ 0.998. The results revealed a significant load-bearing capacity and stiffness of the rat abdomen compared to the rat back tissues. In addition, the mice abdomen showed a higher stiffness in the axial direction in comparison with circumferential one, while the mice back displayed its highest stiffness in the circumferential direction. The material coefficients of the rat and mice skin tissues were determined and well compared to the experimental data. The optimized fiber angles were also compared to the experimental histological data, and in all cases less than 11.85% differences were observed in both the skin tissues.

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Atherosclerosis is considered as the most severe form of cardiovascular diseases as it alters the structure of the elastin and collagen and, consequently, the mechanical properties of the artery wall. The role of collagen fibers orientations in the mechanical properties of the healthy and atherosclerotic human coronary arteries so far has not been well determined. In this study, a fiber family based constitutive equation was employed to address the mechanical behavior of healthy and atherosclerotic human coronary arteries using the combination of histostructural and uniaxial data. A group of six healthy and atherosclerotic human coronary arteries was excised at autopsy and histological analyses were performed on each artery to determine the mean angle of collagen fibers. The preconditioned arterial tissues were then subjected to a series of quasi-static axial and circumferential loadings. The key role of fiber orientation was explicitly added into a proposed strain energy density function. The constrained nonlinear optimization method was used to determine the material coefficients based on the axial and circumferential extension data of the arteries. The material coefficients of coronary arteries were given with R(2)≥0.991. The results regardless of loading direction revealed a significant load-bearing capacity and stiffness of atherosclerotic arteries compared to the healthy ones (p<0.005). The optimized fiber angles were in good agreement with the experimental histological data as only 2.52% and 10.10% differences were observed for the healthy and atherosclerotic arteries, respectively. The stored energy function of the healthy arteries was found to be higher than that of atherosclerotic ones. These findings help us to understand the directional mechanical properties of coronary arteries which may have implications for different types of interventions and surgeries, including bypass, stenting, and balloon-angioplasty.

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The objective of this study was to measure and model the passive biomechanics of cadaveric levator ani muscle in the fiber direction at low strains with a moderately slow deformation rate. Nine levator ani samples, extracted from female cadavers aged 64 to 96 years, underwent preconditioning and uniaxial biomechanical analysis on a tensile testing apparatus after the original width, thickness, and length were measured. The load extension data and measured dimensions were used to calculate stress-strain curves for each sample. The resulting stress-strain curves up to 10% strain were fit to four different constitutive models to determine which model was most appropriate for the data. A power-law model with two parameters was found to fit the data most accurately. Constitutive parameters did not correlate significantly with age in this study; this may be because all of the cadavers were postmenopausal.

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A survey of experimental data from the literature in cases where the deformation of a specimen is varied continuously from uniaxial compression to tensile deformation shows that Young's Modulus M, defined as the limit of stress to strain in the undeformed state, is independent of the direction of approach to the limit. The normalized stress-strain relation of Martin, Roth, and Stiehler (MRS, 1956) is F/M = (L-1 - L-2) exp A (L - L-1) where F is the stress on the undeformed section, L is the extension ratio, and M and A are constants. Values of M and A are obtained from the intercept and slope of a graph of experimental observations of log F/(L-1 - L-2) against (L - 1-1) including observations of uniaxial compression if available. They found the value of A to he about 0.38 for pure-gum vulcanizates of natural rubber and several synthetics. In later work several observers have now found that the equation is also valid for vulcanizates containing a filler, but A is higher, reaching a value of about 1 for large amounts of filler. In extreme cases A is not constant at low deformations. The range of applicability in many cases now is found to extend from the compressive region where L = 0.5 up to the point of tensile rupture or to a point where A increases abruptly because of crystallization. Taking A as a constant parameter in the range 0.36 to 1, graphs are presented showing calculated values of (1) F/M as a function of L and (2) the normalized Mooney-Rivlin plot of F/[2M(L - L-2)] against L-1. Each of the latter graphs has only a limited region of linearity corresponding to constant values of the Mooney-Rivlin coefficients C1 and C2. Since this region does not include the undeformed state, where L = 1, or any of the compression region, the utility of the Mooney-Rivlin equation is extremely limited, since it can not be used at low elongations. The coefficients are dramatically altered for rubbers showing different values of the MRS constant A. For rubbers showing the higher values of A, the coefficients are radically altered and the region of approximate linearity is drastically reduced.