Fiber Stretch Research Articles

Highly secure OFDM scheme based on multi-level masking and performance-enhanced key accompanying transmission.

In this Letter, we propose a highly secure OFDM scheme based on multi-level masking and performance-enhanced key-accompanying transmission. Our scheme exploits a four-dimensional hyperchaotic model and uses subcarriers and symbols to scramble the signal, thereby achieving chaotic encryption and enhancing system security. The dual-mode index technique is employed to conceal the key within the encrypted signal, enabling cooperative transmission of both the key and the signal. We conducted experiments that successfully transmitted a 28 Gb/s dual-mode QPSK (DM-QPSK) signal and a 42 Gb/s dual-mode 8QAM (DM-8QAM) signal over a 2-km stretch of 7-core fiber. The results demonstrated that our proposed key-accompanying transmission scheme did not compromise the system's transmission performance. Moreover, the key space of this scheme is as large as 10135, effectively ensuring system security. Under the received optical power corresponding to the bit error rate of 3.8 × 10-3, the minimum number of key repetitions in DM-8QAM that makes the key bit error rate zero is less than 9 times. This demonstrates that our proposed scheme effectively enhances the transmission performance of the key, achieving high-quality joint transmission of both the key and the signal.

A continuum model for the mechanics of elastomeric sheets reinforced with extensible bidirectional fibers resistant to lateral pressure

We investigate the concurrent three-dimensional (in-plane and out-of-plane) deformations of fiber-reinforced composite (FRC) sheets undergoing lateral pressure. This involves the utilization of the Neo-Hookean strain energy model for the matrix material and computing the strain energy of bidirectional fibers by accounting for the stretching, bending, and twisting responses of the fibers. The kinematics of FRC are formulated within the framework of differential geometry on FRC surfaces, including the computations of the first and second gradient of deformation. By employing the variational principles, we derive the Euler equations describing the mechanics of the fiber–matrix composite system subjected to lateral pressure. The resulting three-dimensional continuum model theoretically predicts the deformation of the matrix material and it is found that the maximum deformation of matrix material occurs in the diagonal direction of the domain, yet, the center of the domain suffers weak in-plane deformation because of surface tension equilibrium. In addition, the stretching, bending, and twisting kinematics of fiber units are computed to investigate the effects of the individual fiber’s kinematics on the overall deformation of fiber meshwork. Lastly, it is found that the lateral pressure on the FRC surface induces fiber flexure in the vicinity of domain boundaries and fiber stretch inside the domain, corresponding to the intensified shrinking strain near the edges and stretching strain in the middle of the domain. The theoretical results provide phenomenologically meaningful insights into comprehending the damage patterns of the fiber-reinforced building material, the hemispherical dome shaping results of bamboo Poly (lactic) acid (PLA) composites and the out-of-plane deformation of woven fabric.

Compressive instabilities enable cell-induced extreme densification patterns in the fibrous extracellular matrix: Discrete model predictions.

We present a new model and extensive computations that explain the dramatic remodelling undergone by a fibrous collagen extracellular matrix (ECM), when subjected to contractile mechanical forces from embedded cells or cell clusters. This remodelling creates complex patterns, comprising multiple narrow localised bands of severe densification and fiber alignment, extending far into the ECM, often joining distant cells or cell clusters (such as tumours). Most previous models cannot capture this behaviour, as they assume stable mechanical fiber response with stress an increasing function of fiber stretch, and a restriction to small displacements. Our fully nonlinear network model distinguishes between two types of single-fiber nonlinearity: fibers that undergo stable (supercritical) buckling (as in previous work) versus fibers that suffer unstable (subcritical) buckling collapse. The model allows unrestricted, arbitrarily large displacements (geometric nonlinearity). Our assumptions on single-fiber instability are supported by recent simulations and experiments on buckling of individual beams with a hierarchical microstructure, such as collagen fibers. We use simple scenarios to illustrate, for the first time, two distinct compressive-instability mechanisms at work in our model: unstable buckling collapse of single fibers, and snap-through of multiple-fiber groups. The latter is possible even when single fibers are stable. Through simulations of large fiber networks, we show how these instabilities lead to spatially extended patterns of densification, fiber alignment and ECM remodelling induced by cell contraction. Our model is simple, but describes a very complex, multi-stable energy landscape, using sophisticated numerical optimisation methods that overcome the difficulties caused by instabilities in large systems. Our work opens up new ways of understanding the unique biomechanics of fibrous-network ECM, by fully accounting for nonlinearity and associated loss of stability in fiber networks. Our results provide new insights on tumour invasion and metastasis.

Predicting Myosin Heavy Chain Isoform Through Muscle Fiber Length in Older Adults

Myosin heavy chain (MHC) isoforms directly impact muscle cellular contractile characteristics and are closely associated with other cellular functions (substrate metabolism, calcium handling, etc.). As such, MHC isoform has come to define muscle “fiber type” (MHC I = slow/oxidative and MHC II = fast/glycolytic). Due to the heterogeneity of MHC isoforms expressed within human skeletal muscle tissue, it is essential to determine MHC isoform to allow proper interpretation of tissue level outcomes that may arise from variations within or between fiber types. A priori estimation of fiber type would be a useful tool for ensuring even distribution of fiber type when considering cellular assays in which MHC isoform can only be determined after the fact. Based on the assumption that fibers of various MHC isoform would differently resist mechanical strain, we’ve demonstrated that MHC I fibers can be distinguished from MHC II fibers based on the ratio of fiber to bundle length (degree of stretch) during mechanical dissection. However, our approach used samples from healthy young adults and has not been tested in tissue from older adults, where cellular stiffness is likely elevated. Therefore, our objective is to test our ability to predict MHC isoform in older adults. We hypothesize that muscle fiber strain following dissection will predict MHC isoform in older adults. Methods: Muscle biopsies from the vastus lateralis muscle were obtained from two older adults (one male, one female). A total of 129 muscle fibers were dissected and measured. Fibers were then stored individually and MHC isoform was subsequently identified via sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-Page). Receiver Operating Characteristics (ROC) and confusion matrix were used to assess the predictive capacity for fiber stretch on activation as an index of fiber type. Data: An ROC area under curve (AUC) of 0.634 which indicates that there is a relatively low predictive capacity. Summary: This study aimed to test the feasibility of an approach for predicting muscle fiber type through changes in fiber length upon mechanical dissection. Established in young adults, this study tested samples obtained from older adults to explore the potential effects of age. Preliminary data show that muscle fiber length can predict muscle fiber type in older adults, though the accuracy may be limited when compared with the same approach in younger adults. This lack of accuracy may be attributed to the increase in stiffness that occurs with age, limiting the capacity for strain and thus fiber type variability. A new threshold may need to be determined to increase the accuracy of fiber type prediction. Conclusion: Preliminary data shows that fiber length can provide a prediction for MHC isoform in older adults. NIH National Institute on Aging (1R21AG077125-01A1) and Achievement Rewards for College Scientists (ARCS) Oregon. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Finite Element Model of the Shoulder with Active Rotator Cuff Muscles: Application to Wheelchair Propulsion.

The rotator cuff is prone to injury, remarkably so for manual wheelchair users. To understand its pathomechanisms, finite element models incorporating three-dimensional activated muscles are needed to predict soft tissue strains during given tasks. This study aimed to develop such a model to understand pathomechanisms associated with wheelchair propulsion. We developed an active muscle model associating a passive fiber-reinforced isotropic matrix with an activation law linking calcium ion concentration to tissue tension. This model was first evaluated against known physiological muscle behavior; then used to activate the rotator cuff during a wheelchair propulsion cycle. Here, experimental kinematics and electromyography data was used to drive a shoulder finite element model. Finally, we evaluated the importance of muscle activation by comparing the results of activated and non-activated rotator cuff muscles during both propulsion and isometric contractions. Qualitatively, the muscle constitutive law reasonably reproduced the classical Hill model force-length curve and the behavior of a transversally loaded muscle. During wheelchair propulsion, the deformation and fiber stretch of the supraspinatus muscle-tendon unit pointed towards the possibility for this tendon to develop tendinosis due to the multiaxial loading imposed by the kinematics of propulsion. Finally, differences in local stretch and positions of the lines of action between activated and non-activated models were only observed at activation levels higher than 30%. Our novel finite element model with active muscles is a promising tool for understanding the pathomechanisms of the rotator cuff for various dynamic tasks, especially those with high muscle activation levels.

On the inflation, bulging/necking bifurcation and post-bifurcation of a cylindrical membrane under limited extensibility of its constituents

We consider the bifurcation and post-bifurcation of an extended and inflated circular cylindrical membrane under limited extensibility of its constituents. First, for illustration of the limited extensibility effect, a membrane made of the (isotropic) Gent model is briefly analyzed. Second, the membrane is considered to be made of an isotropic ground substance reinforced with fibers symmetrically arranged in two helically distributed families which are mechanically equivalent. The mechanical behavior of the fibers in a similar way to the (isotropic) Gent model is taken to reflect fiber limited extensibility. In particular, the materials under consideration are NH models augmented with two functions called reinforcing models, each one accounting for unidirectional reinforcement. For a specific material, since both families are mechanically equivalent, the reinforcing models are equal. The nature of the anisotropy considered, i.e., the reinforcing model, can depend only on the stretch in the fiber direction or can depend on the fiber stretch and also can have an influence on the shear response of the material (i.e., it also captures shearing in the fiber direction). The limitation associated with the material anisotropic deformability as well as the arrangement of the material constituents is discussed with respect to the initiation of bulging and necking for the membrane. The subsequent consequences for configurations in equilibrium during post-bifurcation are also studied in detail and a variety of results are given in terms of the limited extensibility (deformability) of the fibers as well as their mechanical response and arrangement (fiber winding angle).

Association of elastic power in mechanical ventilation with the severity of acute respiratory distress syndrome: a retrospective study

BackgroundMechanical power (MP) is the total energy released into the entire respiratory system per minute which mainly comprises three components: elastic static power, Elastic dynamic power and resistive power. However, the energy to overcome resistance to the gas flow is not the key factor in causing lung injury, but the elastic power (EP) which generates the baseline stretch of the lung fibers and overcomes respiratory system elastance may be closely related to the ARDS severity. Thus, this study aimed to investigate whether EP is superior to other ventilator variables for predicting the severity of lung injury in ARDS patients.MethodsWe retrieved patient data from the Medical Information Mart for Intensive Care III (MIMIC-III) database. The retrieved data involved adults (≥ 18 years) diagnosed with ARDS and subjected to invasive mechanical ventilation for ≥ 48 h. We employed univariate and multivariate logistic regression analyses to investigate the correlation between EP and development of moderate-severe ARDS. Furthermore, we utilized restricted cubic spline models to assess whether there is a linear association between EP and incidence of moderate-severe ARDS. In addition, we employed a stratified linear regression model and likelihood ratio test in subgroups to identify potential modifications and interactions.ResultsModerate-severe ARDS occurred in 73.4% (296/403) of the patients analyzed. EP and MP were significantly associated with moderate-severe ARDS (odds ratio [OR] 1.21, 95% confidence interval [CI] 1.15–1.28, p < 0.001; and OR 1.15, 95%CI 1.11–1.20, p < 0.001; respectively), but EP showed a higher area-under-curve (95%CI 0.72–0.82, p < 0.001) than plateau pressure, driving pressure, and static lung compliance in predicting ARDS severity. The optimal cutoff value for EP was 14.6 J/min with a sensitivity of 75% and specificity of 66%. Quartile analysis revealed that the relationship between EP and ARDS severity remained robust and reliable in subgroup analysis.ConclusionEP is a good ventilator variable associated with ARDS severity and can be used for grading ARDS severity. Close monitoring of EP is advised in patients undergoing mechanical ventilation. Additional experimental trials are needed to investigate whether adjusting ventilator variables according to EP can yield significant improvements in clinical outcomes.

The Effect of Planting Dates and Planting Methods on Cotton Quantitative and Qualitative Traits in Moderate and Humid Climatic Conditions

otton is one of the most important crops in Golestan Province, Iran. The planting and harvesting date interferes with autumn crops such as wheat. A delay in planting cotton causes a decrease in yield. Transplanting cultivation can help to solve this problem. For this purpose, an experiment was carried out during two crop years in 2017 and 2018 in Iran, Golestan Province, Gorgan city, research station of Iraqi Mahlah in the form of a split plot based on randomized complete blocks design in four replications. Experimental treatments including planting dates at three levels including; Planting dates were May 27, June 16 and July 7 and planting methods were in seven levels (6 treatments using Transplanting and direct seeding methods). Quantitative traits including plant height, number of bolls per plant, lint weight per boll, lint yield and biological yield were measured along with cotton qualitative traits such as fiber length, stretch percentage, fiber fineness, fiber strength and uniformity index. Based on the results, the simple effect of planting dates, planting methods, as well as the interaction effect of planting dates × planting methods on all quantitative and qualitative traits were significant. Also, the interaction effect of year × planting date × planting method on the number of bolls per plant and biological yield was significant. The average lint yield in transplanting methods was 2256 kg per hectare and showed an increase of about 37% compared to direct seeding cultivation method. The best cultivation method it was that one with one seedling transplanted, the distance between the rows=75 cm and the distance on the rows=40 cm, the yields being higher as compared to other treatments. In general, the lint yield in direct seeding was much lower than the lint yield in transplanting cultivation. Also, the quality traits were affected by planting dates and planting methods, and in most cases, cotton quality traits were improved in the transplanting cultivation method. Therefore, if the cost of producing and transporting seedlings is economical, cotton transplanting is preferable to direct seeding cultivation.

On-chip light sheet illumination for nanoparticle tracking in microfluidic channels.

A simple and inexpensive method is presented to efficiently integrate light sheet illumination in a microfluidic chip for dark-field microscopic tracking and sizing of nanoparticles. The basic idea is to insert an optical fiber inside a polydimethylsiloxane (PDMS) elastomer microfluidic chip and use it as a cylindrical lens. The optical fiber is in this case no longer seen as only an optical waveguide but as a ready-made micro-optical component that is inexpensive and easy to source. Upon insertion, the optical fiber stretches the PDMS microchannel walls, which has two effects. The first effect is to tone down the intrinsic ripples in the PDMS that would otherwise create inhomogeneities in the light sheet illumination. The second effect is to remove any obliqueness of the channel wall and constrain it to be strictly perpendicular to the propagation of the illumination, avoiding the formation of a prismatic diopter. Through calculations, numerical simulations and measurements, we show that the optimal configuration consists in creating a slowly converging light sheet so that its axial thickness is almost uniform along the tracked area. The corresponding thickness was estimated at 12 μm, or 10 times the depth of field of the optical system. This leads to an at least six-fold increase in the signal-to-noise ratio compared to the case without the cylindrical lens. This original light-sheet configuration is used to track and size spherical gold nanoparticles with diameters of 80 nm and 50 nm.

Transglutaminase 2 has higher affinity for relaxed than for stretched fibronectin fibers

Transglutaminase 2 (TG2) plays a vital role in stabilizing extracellular matrix (ECM) proteins through enzymatic crosslinking during tissue growth, repair, and inflammation. TG2 also binds non-covalently to fibronectin (FN), an essential component of the ECM, facilitating cell adhesion, migration, proliferation, and survival. However, the interaction between TG2 and fibrillar FN remains poorly understood, as most studies have focused on soluble or surface-adsorbed FN or FN fragments, which differ in their conformations from insoluble FN fibers. Using a well-established in vitro FN fiber stretch assay, we discovered that the binding of a crosslinking enzyme to ECM fibers is mechano-regulated. TG2 binding to FN is tuned by the mechanical tension of FN fibers, whereby TG2 predominantly co-localizes to low-tension FN fibers, while fiber stretching reduces their affinity for TG2. This mechano-regulated binding relies on the proximity between the N-terminal β-sandwich and C-terminal β-barrels of TG2. Crosslinking mass spectrometry (XL-MS) revealed a novel TG2-FN synergy site within TG2’s C-terminal β-barrels that interacts with FN regions located outside of the canonical gelatin binding domain, specifically FNI2 and FNIII14–15. Combining XL-MS distance restraints with molecular docking revealed the mechano-regulated binding mechanism between TG2 and modules FNI7–9 by which mechanical forces regulate TG2-FN interactions. This highlights a previously unrecognized role of TG2 as a tension sensor for FN fibers. This novel interaction mechanism has significant implications in physiology and mechanobiology, including how forces regulate cell adhesion, spreading, migration, phenotype modulation, depending on the tensional state of ECM fibers. Data are available via ProteomeXchange with identifier PXD043976.

Univariate Gauss quadrature for structural modelling of tissues and materials with distributed fibres

This work presents a method for computing the averaged free energy and constitutive relations in hyperelastic material models with distributed fibres, as they apply to soft fibre-reinforced materials and biological tissues. While these models are currently implemented through either spherical cubature of the fibre free energy or its Taylor series, we here propose a new method based on a univariate Gauss quadrature rule with integration points and weights informed by the statistical moments of the distribution of fibre stretch. As an intrinsic property, the new approach separates the integration of the fibre constitutive law from the integration of the orientation distribution, the latter leading to structural tensors of even order. Provided the latter 2n−1 tensors are computed accurately up to tensorial order 2(2n−1), the method integrates exactly any polynomial of order 2n−1 that agrees with the fibre law at the n integration points. After formally introducing the quadrature method for generally non-affine fibre deformations and arbitrary order, we focus on the important special case of affine fibre kinematics and discuss the rules with n≤3 integration points, for which the corresponding positions and weights are determined analytically. At a computational cost comparable to the existing approaches, the new method does not require the fibre law to be analytic and can thus robustly deal with piece-wise definitions of the fibre energy, in contrast to Taylor-series approaches, and it does not induce additional anisotropy as it can occur with spherical cubature rules. The 3-point rule is further investigated and illustrated in numerical examples relating to soft collagenous tissues based on a Fortran implementation of the method suitable for use in finite element analyses.

Muscle preflex response to perturbations in locomotion: In vitro experiments and simulations with realistic boundary conditions.

Neuromuscular control loops feature substantial communication delays, but mammals run robustly even in the most adverse conditions. In vivo experiments and computer simulation results suggest that muscles' preflex-an immediate mechanical response to a perturbation-could be the critical contributor. Muscle preflexes act within a few milliseconds, an order of magnitude faster than neural reflexes. Their short-lasting action makes mechanical preflexes hard to quantify in vivo. Muscle models, on the other hand, require further improvement of their prediction accuracy during the non-standard conditions of perturbed locomotion. Our study aims to quantify the mechanical work done by muscles during the preflex phase (preflex work) and test their mechanical force modulation. We performed in vitro experiments with biological muscle fibers under physiological boundary conditions, which we determined in computer simulations of perturbed hopping. Our findings show that muscles initially resist impacts with a stereotypical stiffness response-identified as short-range stiffness-regardless of the exact perturbation condition. We then observe a velocity adaptation to the force related to the amount of perturbation similar to a damping response. The main contributor to the preflex work modulation is not the change in force due to a change in fiber stretch velocity (fiber damping characteristics) but the change in magnitude of the stretch due to the leg dynamics in the perturbed conditions. Our results confirm previous findings that muscle stiffness is activity-dependent and show that also damping characteristics are activity-dependent. These results indicate that neural control could tune the preflex properties of muscles in expectation of ground conditions leading to previously inexplicable neuromuscular adaptation speeds.

Reading Anna Frajlich's Latest Volume of Poetry

Reading Anna Frajlich's Latest Volume of Poetry

Cerveau maternel : Théorie bayésienne de l’intéroception maternelle pendant la grossesse et le postpartum

The perinatal period, including pregnancy and postpartum, causes major morphological, endocrinal, and thermal transitions in women. As the fetus grows, abdominal muscle fibers stretch, internal organs such as the bladder or colon move, and the uterine anatomy changes. Many of these changes involve interoception, the perception of internal body signals such as muscle and visceral sensations. Despite the importance of these interoceptive signals, few studies have explored perinatal interoception. We propose an innovative theory of maternal interoception based on recent findings in neuroscience. We show that interoceptive signals processing during pregnancy is crucial for understanding perinatal phenomenology and psychopathology, such as maternal perception of fetal movements, maternal-infant bonding, denial of pregnancy, phantom fetal movements after childbirth, pseudocyesis or even puerperal delusion. Knowing the importance of these interoceptive mechanisms, clinicians in obstetrics, gynecology and mental health should be particularly vigilant to maternal interoception during the perinatal period.

A model of optical fiber point-to-point communication system

The waveguide which is considered recently for transmission of radio frequency (RF) signals from one node to another node is the optic fiber technology. The reliance on fast transmission of information can be achieved with the implementation of fiber optic cable as a waveguide in a communication channel. Basically, optic fiber transmits information with the aid of light called laser at majorly two categories of wavelengths which are 1310 nm and 1550 nm. Propagation of signal over a long stretch of fiber is affected by attenuation due to scattering, fiber bend due to impurities and absorption between the core and the cladding when signal travels along the channel, but these loses are minimal between acceptable value. Optical fiber sensors called photodetector are used to detect the information at the receiving end with minimal losses along the fiber channel. Results obtained demonstrate that there are minimal losses in a fiber cable-based signal transmission.

Improving Transverse Compressive Modulus of Carbon Fibers during Wet Spinning of Polyacrylonitrile

The performance of carbon fibers depends on the properties of the precursor polyacrylonitrile (PAN) fibers. Stretching of PAN fibers results in improved tensile properties, while potentially reducing its compressive properties. To determine optimization trade-offs, the effect of coagulation conditions and the stretching process on the compressive modulus in the transverse direction (ET) was investigated. A method for accurately determining ET from polymer fibers with non-circular cross-sectional shapes is presented. X-ray diffraction was used to measure the crystallite size, crystallinity, and crystallite orientation of the fibers. ET was found to increase with decreasing crystallite orientation along the drawing direction, which decreases the tensile modulus in the longitudinal direction (EL) proportionally to crystallite orientation. Stretching resulted in greater crystallite orientation along the drawing direction for fibers formed under the same coagulation conditions. Increasing the solvent concentration in the coagulation bath resulted in a higher average orientation, but reduced the impact of stretching on the orientation. The relationship between ET and EL observed in the precursor PAN fiber is retained after carbonization, with a 20% increase in ET achieved for a 2% decrease in EL. This indicates that controlled stretching of PAN fiber allows for highly efficient trading off of EL for ET in carbon fiber.

An increase in force after stretch of diaphragm fibers and myofibrils is accompanied by an increase in sarcomere length nonuniformities and Ca2+ sensitivity.

When muscle fibers from limb muscles are stretched while activated, the force increases to a steady-state level that is higher than that produced during isometric contractions at a corresponding sarcomere length, a phenomenon known as residual force enhancement (RFE). The mechanisms responsible for the RFE are an increased stiffness of titin molecules that may lead to an increased Ca2+ sensitivity of the contractile apparatus, and the development of sarcomere length nonuniformities. RFE is not observed in cardiac myofibrils, which makes this phenomenon specific to certain preparations. The aim of this study was to investigate whether the RFE is present in the diaphragm, and its potential association with an increased Ca2+ sensitivity and the development of sarcomere length nonuniformities. We used two preparations: single intact fibers and myofibrils isolated from the diaphragm of mice. We investigated RFE in a variety of lengths across the force-length relationship. RFE was observed in both preparations at all lengths investigated and was larger with increasing magnitudes of stretch. RFE was accompanied by an increased Ca2+ sensitivity as shown by a change in the force-pCa2+ curve, and increased sarcomere length nonuniformities. Therefore, RFE is a phenomenon commonly observed in skeletal muscles, with mechanisms that are similar across preparations.

Kawabata Analysis of Cotton Denim Fabrics Treated with Industrial Washing Techniques

ABSTRACT Garment washing of denim fabrics is essential for fading of color, aesthetic effects, vintage look and improvement in handle properties of resulting garments. Denim fabrics of two types, one standard fabric (non-stretch) and other with 2% elastane fiber (stretch), are washed with different industrial washing techniques on Tonello sampling machine. The objective evaluation of handle and mechanical properties of the washed samples are carried out on Kawabata evaluation system (KES-F). Five main characteristics of fabrics are evaluated on KES-F system. The mechanical properties like tensile energy, extensibility and compression energy have increased for both stretch and non-stretch fabrics, while bending stiffness and bending hysteresis have decreased for both types of washed fabrics. The geometrical surface roughness and coefficient of friction have slightly increased after employed washing techniques. The optical microscope is used to investigate the surface changes of the fabric after the employed washing techniques.

On the effect of irregular uterine activity during a vaginal delivery using an electro-chemo-mechanical constitutive model

During a normal vaginal delivery, the muscle cells propagate electrical signals throughout the uterine wall, resulting in uterine contractions. However, uncoordinated uterine activity may disturb the uterine contractions pattern and negatively impact fetal and maternal health. Some of the abnormalities identified by the specialists are excessively short resting intervals and tachysystole. This work aims to investigate the influence of abnormal uterine activity in terms of maximum principal stress distribution and collagen fibers stretch in the uterine tissue during vaginal delivery with (i) excessively short resting intervals without changing the contraction time, and (ii) tachysystole (contraction and reduced resting times). These patterns are compared with a normal uterine contraction pattern. To achieve our aims, a biomechanical model was developed, including finite element models of the uterus and the fetus, and an electro-chemo-mechanical constitutive model. Generally, the excessively short resting intervals exhibit higher average maximum principal stresses during the contraction and resting stages, lower average fibers stretch values in the longitudinal direction and higher stretch in the circumferential direction. On the other hand, the tachysystole exhibit generally lower stress values during the uterine contraction and higher stress values during the resting stages, higher stretch in the longitudinal direction, and lower stretch in the circumferential direction.

Fibre stretch models of transversely isotropic incompressible hyperelasticity

A new strain–energy function for incompressible transversely isotropic non-linearly hyperelastic materials is obtained by assuming that the deviatoric stress in the preferred direction is a function only of the stretch in that direction. The model is an additive combination of two arbitrary functions of the strain invariants, one of which is an arbitrary function of the fibre stretch. The behaviour of the model for the canonical deformations of simple tension and shear is analysed. It is shown that the stress–stretch response in simple tension along and perpendicular to the fibres is determined by the fibre stretch function alone. It is also shown that a linearisation of the general model containing only three arbitrary constants is an excellent fit to a comprehensive experimental data set of other authors for simple tension along and perpendicular to the fibres and simple shear along the fibres.