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1.
J Biomech Eng ; 145(1)2023 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-35838330

RESUMO

Reactive viscoelasticity is a theoretical framework based on the theory of reactive constrained mixtures that encompasses nonlinear viscoelastic responses. It models a viscoelastic solid as a mixture of strong and weak bonds that maintain the cohesiveness of the molecular constituents of the solid matter. Strong bonds impart the elastic response while weak bonds break and reform into a stress-free state in response to loading. The process of bonds breaking and reforming is modeled as a reaction where loaded bonds are the reactants and bonds reformed into a stress-free state are the products of a reaction. The reaction is triggered by the evolving state of loading. The state of stress in strong bonds is a function of the total strain in the material, whereas the state of stress in weak bonds is based on the state of strain relative to the time that these bonds were reformed. This study introduces two important practical contributions to the reactive nonlinear viscoelasticity framework: (1) normally, the evaluation of the stress tensor involves taking a summation over a continually increasing number of weak bond generations, which is poorly suited for a computational scheme. Therefore, this study presents an effective numerical scheme for evaluating the strain energy density, the Cauchy stress, and spatial elasticity tensors of reactive viscoelastic materials. (2) We provide the conditions for satisfying frame indifference for anisotropic nonlinear viscoelasticity, including for tension-bearing fiber models. Code verifications and model validations against experimental data provide evidence in support of this updated formulation.


Assuntos
Modelos Biológicos , Dinâmica não Linear , Anisotropia , Elasticidade , Estresse Mecânico , Viscosidade
2.
J Mol Graph Model ; 117: 108324, 2022 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-36103785

RESUMO

Concurrent multiscale methods have been developed to reduce the degrees of freedom and reduce the effects of boundary conditions on the results of atomic simulations. In this paper, two simplified concurrent multiscale methods, one with handshake region and another without handshake region are used to investigate the nanoindentation process on a single crystal of Al at room temperature. The multiscale models are validated by observing reasonably well similarities in the load-depth curves obtained from multiscale and full MD simulations. Refining the element size down to atomic spacing resulted in high computational efforts while the analysis results do not improve significantly. Also, it is shown that by defining the thermostat in the atomistic part, wave reflections are eliminated at the interface of atomic and continuum domains. It is shown that by selecting appropriate dimensions of the atomic domain, there is no need to use nonlinear elasticity in the continuum region. Also, hardness is more affected by sample size than the elastic modulus.


Assuntos
Elasticidade , Módulo de Elasticidade , Dureza
3.
Int J Mol Sci ; 23(17)2022 Aug 30.
Artigo em Inglês | MEDLINE | ID: mdl-36077234

RESUMO

Titin is the largest protein in humans, composed of more than one hundred immunoglobulin (Ig) domains, and plays a critical role in muscle's passive elasticity. Thus, the molecular design of this giant polyprotein is responsible for its mechanical function. Interestingly, most of these Ig domains are connected directly with very few interdomain residues/linker, which suggests such a design is necessary for its mechanical stability. To understand this design, we chose six representative Ig domains in titin and added nine glycine residues (9G) as an artificial interdomain linker between these Ig domains. We measured their mechanical stabilities using atomic force microscopy-based single-molecule force spectroscopy (AFM-SMFS) and compared them to the natural sequence. The AFM results showed that the linker affected the mechanical stability of Ig domains. The linker mostly reduces its mechanical stability to a moderate extent, but the opposite situation can happen. Thus, this effect is very complex and may depend on each particular domain's property.


Assuntos
Conectina/química , Proteínas Musculares , Dobramento de Proteína , Conectina/metabolismo , Elasticidade , Humanos , Domínios de Imunoglobulina , Proteínas Musculares/metabolismo
4.
J Biomech ; 143: 111302, 2022 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-36126503

RESUMO

The gastric biomechanics influences digestive function as well as a range of topics of medical and scientific interests such as interaction between the stomach and gastric devices. Hence, the mechanical properties are essential for understanding gastric tissue and function in health and disease, and for the development of diagnostic or therapeutic devices. A key characteristic to be characterized is the time dependent mechanical tissue properties. The aim of this study was to characterize viscoelastic properties of the stomach across a frequency range. Longitudinal and circumferential stomach samples from the porcine fundus, corpus and antrum were pre-stretched 10 % and sinusoidally loaded with 10 % dynamic strain. The viscoelastic properties were assessed from 0.01 - 15 Hz using dynamic mechanical analysis. The storage moduli, loss moduli and tan δ had a significant second-order polynomial trend with increasing frequency. For the loss moduli, significant differences were observed between 0.01 and 15 Hz and between 0.05 and 15 Hz (p = 0.023 to 0.041). Significant differences were not found for storage moduli. Tan δ was frequency-independent, indicating that the two moduli varied proportionally. Fundus had significantly smaller storage moduli for longitudinal samples compared to corpus (p = 0.034) and antrum (p = 0.014) but was not significantly different for circumferential samples. Analysis of direction-dependency showed significant differences between longitudinal and circumferential samples (p = 0.002 to 0.042). The presented work provides insight into tensile viscoelastic properties of gastric tissue, which is useful for developing biomaterials, devices and computational models for device development specification calibrations.


Assuntos
Estômago , Triacetonamina-N-Oxil , Animais , Materiais Biocompatíveis , Elasticidade , Estresse Mecânico , Suínos , Viscosidade
5.
Diving Hyperb Med ; 52(3): 208-212, 2022 Sep 30.
Artigo em Inglês | MEDLINE | ID: mdl-36100932

RESUMO

BACKGROUND: Hyperbaric oxygen treatment (HBOT) is often used in an attempt to reverse/treat late radiation-induced tissue fibrosis (LRITF). This study aimed to quantify the effects on skin elasticity. METHODS: Skin retraction time was used as a marker of skin elasticity in 13 irradiated breast cancer patients. The measurements were carried out on the affected side as well as the unaffected/healthy side at a mirrored location. Readings were taken at the start and end of HBOT (mean 43 sessions, 80 min at 243 kPa). RESULTS: Patient age ranged from 39-70 years. All patients underwent surgical lumpectomy and radiotherapy prior to undergoing HBOT. The mean time between radiotherapy and HBOT was 70 months. Seven of the 13 patients underwent chemotherapy. Mean irradiated skin retraction time improved from 417 (SD 158) pre-HBOT to 171 (24) msec post-HBOT (P < 0.001). Mean pre-HBOT retraction time in the non-irradiated skin was 143 (20) msec and did not change. CONCLUSIONS: This promising pilot study that suggests that HBOT may improve skin elasticity in patients with LRITF.


Assuntos
Oxigenoterapia Hiperbárica , Lesões por Radiação , Adulto , Idoso , Elasticidade , Humanos , Pessoa de Meia-Idade , Oxigênio , Projetos Piloto , Lesões por Radiação/terapia
6.
Annu Int Conf IEEE Eng Med Biol Soc ; 2022: 17-20, 2022 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-36085603

RESUMO

Optical tweezer is a non-contact tool to trap and manipulate microparticles such as biological cells using coherent light beams. In this study, we utilized a dual-beam optical tweezer, created using two counterpropagating and slightly divergent laser beams to trap and deform biological cells. Human embryonic kidney 293 (HEK-293) and breast cancer (SKBR3) cells were used to characterize their membrane elasticity by optically stretching in the dual-beam optical tweezer. It was observed that the extent of deformation in both cell types increases with increasing optical trapping power. The SKBR3 cells exhibited greater percentage deformation than that of HEK-293 cells for a given trapping power. Our results demonstrate that the dual-beam optical tweezer provides measures of cell elasticity that can distinguish between various cell types. The non-contact optical cell stretching can be effectively utilized in disease diagnosis such as cancer based on the cell elasticity measures.


Assuntos
Neoplasias da Mama , Pinças Ópticas , Elasticidade , Embrião de Mamíferos , Feminino , Células HEK293 , Humanos
7.
Annu Int Conf IEEE Eng Med Biol Soc ; 2022: 1585-1589, 2022 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-36085803

RESUMO

The physiological origin of the aperiodic signal present in the electrophysiological recordings, called l/f neural noise, is unknown; nevertheless, it has been associated with health and disease. The power spectrum slope, -α in 1/fα, has been postulated to be related to the dynamic balance between excitation (E) and inhibition (I). Our study found that human cerebral organoids grown from induced pluripotent stem cells (iPSCs) from Schizophrenia patients (SCZ) showed structural changes associated with altered elasticity compared to that of the normal cerebral organoids. Furthermore, mitochondrial drugs modulated the elasticity in SCZ that was found related to the changes in the spectral exponent. Therefore, we developed an electro-mechanical model that related the microtubular-actin tensegrity structure to the elasticity and the 1/fα noise. Model-based analysis showed that a decrease in the number and length of the constitutive elements in the tensegrity structure decreased its elasticity and made the spectral exponent more negative while thermal white noise will make α = 0.. Based on the microtubularactin model and the cross-talk in structural (elasticity) and functional (electrophysiology) response, aberrant mitochondrial dynamics in SCZ are postulated to be related to the deficits in mitochondrial-cytoskeletal interactions for long-range transport of mitochondria to support synaptic activity for E/I balance. Clinical Relevance-Our experimental data and modeling present a structure-function relationship between mechanical elasticity and electrophysiology of human cerebral organoids that differentiated SCZ patients from normal controls.


Assuntos
Organoides , Esquizofrenia , Eletrofisiologia Cardíaca , Elasticidade , Humanos , Microscopia de Força Atômica
8.
Annu Int Conf IEEE Eng Med Biol Soc ; 2022: 629-632, 2022 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-36086013

RESUMO

Various studies have looked at the efficiency of artificial vessel and tissue networks in the study of photoplethysmography (PPG) in an effort to better understand the origin of various morphological features present in the signal. Whilst there are all reasonable attempts made to replicate geometrical features such as vessel depth, vessel wall thickness and diameter etc., not many studies have attempted to replicate the mechanical properties such as vessel elasticity and tissue compressibility. This study reports two methods for tissue mechanical testing for the analysis of vessel elasticity and tissue compressibility. A two-part polydimethylsiloxane (PDMS) was used as a base material for both tissue and vessel construction, and the properties altered by changing the curing component ratio. Tissue compression properties were investigated using an industrially calibrated materials testing device using the protocol from the ASTM 0575-91 testing method. Vessel elasticity was investigated using a custom method and apparatus to report vessel diameter and length change simultaneously. Tissue compressive properties proved reasonably easy to replicate through catalyst alteration, however the vessel elasticity properties were found to be higher than expected at all reasonable catalyst ratios. The property of hyper-elasticity was observed in the artificial vessels though, leading to the conclusion that alternative material recipes or construction methods may be needed to correctly replicate the expected mechanical characteristics. Clinical Relevance- The latest generation of health monitoring devices, especially those that are wearable and used widely by individuals wishing to monitor their health daily are becoming smarter and more sophisticated in their functionality. The majority of such devices use photoplethysmography (PPG) as their primary monitoring technique. Being able to replicate the PPG in a phantom allows the continued study and development of devices, and to improve their functionality without the continued need for extensive user-testing.


Assuntos
Testes Mecânicos , Fotopletismografia , Elasticidade , Humanos , Imagens de Fantasmas , Fotopletismografia/métodos
9.
Annu Int Conf IEEE Eng Med Biol Soc ; 2022: 1512-1515, 2022 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-36086082

RESUMO

The knowledge of the biomechanical properties of tissues is useful for different applications such as disease diagnosis and treatment monitoring. Reverberant Shear Wave Elastography (RSWE) is an approach that has reduced the restrictions on wave generation to characterize the shear wave velocity over a range of frequencies. This approach is based on the generation of a reverberant field that is generated by the reflections of waves from inhomogeneities and tissue boundaries that exist in the tissue. The Kelvin-Voigt Fractional Derivative model is commonly used to characterize elasticity and viscosity of soft tissue when using shear wave ultrasound elatography. These viscoelastic characteristics can be then validated using mechanical measurements (MM) such as stress relaxation. During RSWE acquisition, the effect of interface pressure, induced by pushing the probe on the skin through the gel pad, on the viscous and elastic characteristics of tissue can be investigated. However, the effect of interface pressure on the validity of the extracted viscous and elastic characteristics was not investigated before. Therefore, the purpose of this study was to compare the estimation of the viscoelastic parameters at different thickness of gel pad against the viscoelastic characteristics obtained from MM. The experiments were conducted in a tissue-mimicking phantom. The results confirm that the relaxed elastic constant (µ0) can be depreciated. In addition, a higher congruence was found in the viscous parameter (ηα) estimated at 6 and 7 mm. On the other hand, a difference in the order of fractional derivative (α) was found.


Assuntos
Técnicas de Imagem por Elasticidade , Elasticidade , Técnicas de Imagem por Elasticidade/métodos , Imagens de Fantasmas , Ultrassonografia , Viscosidade
10.
Phys Rev Lett ; 129(8): 088001, 2022 Aug 19.
Artigo em Inglês | MEDLINE | ID: mdl-36053686

RESUMO

The problem of characterizing the structure of an elastic network constrained to lie on a frozen curved surface appears in many areas of science and has been addressed by many different approaches, most notably, extending linear elasticity or through effective defect interaction models. In this Letter, we show that the problem can be solved by considering nonlinear elasticity in an exact form without resorting to any approximation in terms of geometric quantities. In this way, we are able to consider different effects that have been unwieldy or not viable to include in the past, such as a finite line tension, explicit dependence on the Poisson ratio, or the determination of the particle positions for the entire lattice. Several geometries with rotational symmetry are solved explicitly. Comparison with linear elasticity reveals an agreement that extends beyond its strict range of applicability. Implications for the problem of the characterization of virus assembly are also discussed.


Assuntos
Elasticidade
11.
Proc Natl Acad Sci U S A ; 119(40): e2208027119, 2022 Oct 04.
Artigo em Inglês | MEDLINE | ID: mdl-36166475

RESUMO

Piezo proteins are mechanosensitive ion channels that can locally curve the membrane into a dome shape [Y. R. Guo, R. MacKinnon, eLife 6, e33660 (2017)]. The curved shape of the Piezo dome is expected to deform the surrounding lipid bilayer membrane into a membrane footprint, which may serve to amplify Piezo's sensitivity to applied forces [C. A. Haselwandter, R. MacKinnon, eLife 7, e41968 (2018)]. If Piezo proteins are embedded in lipid bilayer vesicles, the membrane shape deformations induced by the Piezo dome depend on the vesicle size. We employ here membrane elasticity theory to predict, with no free parameters, the shape of such Piezo vesicles outside the Piezo dome, and show that the predicted vesicle shapes agree quantitatively with the corresponding measured vesicle shapes obtained through cryoelectron tomography, for a range of vesicle sizes [W. Helfrich, Z. Naturforsch. C 28, 693-703 (1973)]. On this basis, we explore the coupling between Piezo and membrane shape and demonstrate that the features of the Piezo dome affecting Piezo's membrane footprint approximately follow a spherical cap geometry. Our work puts into place the foundation for deducing key elastic properties of the Piezo dome from membrane shape measurements and provides a general framework for quantifying how proteins deform bilayer membranes.


Assuntos
Canais Iônicos , Bicamadas Lipídicas , Elasticidade , Canais Iônicos/metabolismo , Bicamadas Lipídicas/metabolismo , Membranas/metabolismo
12.
Proc Natl Acad Sci U S A ; 119(40): e2208034119, 2022 Oct 04.
Artigo em Inglês | MEDLINE | ID: mdl-36166476

RESUMO

We show in the companion paper that the free membrane shape of lipid bilayer vesicles containing the mechanosensitive ion channel Piezo can be predicted, with no free parameters, from membrane elasticity theory together with measurements of the protein geometry and vesicle size [C. A. Haselwandter, Y. R. Guo, Z. Fu, R. MacKinnon, Proc. Natl. Acad. Sci. U.S.A., 10.1073/pnas.2208027119 (2022)]. Here we use these results to determine the force that the Piezo dome exerts on the free membrane and hence, that the free membrane exerts on the Piezo dome, for a range of vesicle sizes. From vesicle shape measurements alone, we thus obtain a force-distortion relationship for the Piezo dome, from which we deduce the Piezo dome's intrinsic radius of curvature, [Formula: see text] nm, and bending stiffness, [Formula: see text], in freestanding lipid bilayer membranes mimicking cell membranes. Applying these estimates to a spherical cap model of Piezo embedded in a lipid bilayer, we suggest that Piezo's intrinsic curvature, surrounding membrane footprint, small stiffness, and large area are the key properties of Piezo that give rise to low-threshold, high-sensitivity mechanical gating.


Assuntos
Canais Iônicos , Bicamadas Lipídicas , Membrana Celular/metabolismo , Elasticidade , Canais Iônicos/metabolismo , Bicamadas Lipídicas/metabolismo , Fenômenos Mecânicos , Mecanotransdução Celular
13.
Sensors (Basel) ; 22(18)2022 Sep 16.
Artigo em Inglês | MEDLINE | ID: mdl-36146379

RESUMO

A recently developed contactless ultrasonic testing scheme is applied to define the optimal saw-cutting time for concrete pavement. The ultrasonic system is improved using wireless data transfer for field applications, and the signal processing and data analysis are proposed to evaluate the modulus of elasticity of early-age concrete. Numerical simulation of leaky Rayleigh wave in joint-half space including air and concrete is performed to demonstrate the proposed data analysis procedure. The hardware and algorithms developed for the ultrasonic system are experimentally validated with a comparison of saw-cutting procedures. In addition, conventional methods for the characterization of early-age concrete, including pin penetration and maturity methods, are applied. The results demonstrated that the developed wireless system presents identical results to the wired system, and the initiation time of leaky Rayleigh wave possibly represents 5% of raveling damage compared to the optimal saw cutting. Further data analysis implies that saw-cutting would be optimally performed at approximately 11.5 GPa elastic modulus of concrete obtained by the wireless and contactless ultrasonic system.


Assuntos
Algoritmos , Ultrassom , Simulação por Computador , Módulo de Elasticidade , Elasticidade
14.
Nat Commun ; 13(1): 5180, 2022 09 02.
Artigo em Inglês | MEDLINE | ID: mdl-36056012

RESUMO

How local stresses propagate through polymeric fluids, and, more generally, how macromolecular dynamics give rise to viscoelasticity are open questions vital to wide-ranging scientific and industrial fields. Here, to unambiguously connect polymer dynamics to force response, and map the deformation fields that arise in macromolecular materials, we present Optical-Tweezers-integrating-Differential -Dynamic-Microscopy (OpTiDMM) that simultaneously imposes local strains, measures resistive forces, and analyzes the motion of the surrounding polymers. Our measurements with blends of ring and linear polymers (DNA) and their composites with stiff polymers (microtubules) uncover an unexpected resonant response, in which strain alignment, superdiffusivity, and elasticity are maximized when the strain rate is comparable to the entanglement rate. Microtubules suppress this resonance, while substantially increasing elastic storage, due to varying degrees to which the polymers buildup, stretch and flow along the strain path, and configurationally relax induced stress. More broadly, the rich multi-scale coupling of mechanics and dynamics afforded by OpTiDDM, empowers its interdisciplinary use to elucidate non-trivial phenomena that sculpt stress propagation dynamics-critical to commercial applications and cell mechanics alike.


Assuntos
Microscopia , Polímeros , Elasticidade , Proteínas Associadas aos Microtúbulos , Pinças Ópticas , Viscosidade
15.
J Manipulative Physiol Ther ; 45(4): 282-289, 2022 May.
Artigo em Inglês | MEDLINE | ID: mdl-36057478

RESUMO

OBJECTIVE: The purpose of this study was to evaluate the effects of Rocabado's 6 × 6 exercises on masseter muscle thickness, muscle elasticity, and pain scores in patients with bruxism. METHODS: A total of 58 participants with bruxism were divided into 2 groups as the exercise group (EG) and control group (CG). A self-care program was applied for the participants in the CG. For those in the EG, in addition to the self-care program, an exercise treatment was performed for 6 days per week for a total of 8 weeks. Using ultrasonography, bilateral masseter muscle thickness and elasticity were assessed before and after treatment. Pain was measured using a visual analog scale. Changes over time within the groups and group-time interactions for continuous variables were assessed using mixed 2-way repeated measures analysis of variance. RESULTS: The improvement in muscle elasticity (P = .015; P = .004) and pain values (P = .049; P = .040) were greater in the EG compared with the CG. There was no significant difference between the 2 groups for masseter muscle thickness (P > .05). CONCLUSION: This study suggests that Rocabado's 6 × 6 exercises are effective in the treatment of muscle elasticity and pain values in participants with bruxism.


Assuntos
Bruxismo , Músculo Masseter , Bruxismo/terapia , Elasticidade , Eletromiografia , Humanos , Músculo Masseter/diagnóstico por imagem , Dor
16.
Soft Matter ; 18(37): 7181-7200, 2022 Sep 28.
Artigo em Inglês | MEDLINE | ID: mdl-36098207

RESUMO

A series of semi-interpenetrating polymer network (semi-IPN) hydrogels based on acrylamide (AAm) and itaconic acid (ITA) was prepared in the presence of different amounts of the natural polymer gelatin (GLN). The semi-IPNs were synthesized by simultaneous polymerization using N,N'-methylene bisacrylamide as a crosslinking agent. A pH-sensitive system was obtained by adding 2 mol% ITA as an anionic comonomer. The effect of GLN content by changing the amine/carboxyl functional groups and incorporating carboxyl groups of ITA in semi-IPN on the swelling, elasticity and physical properties of the hydrogels was investigated. The presence of GLN improved the thermal stability, and the GLN-containing semi-IPNs exhibited a higher degradation temperature compared to the GLN-free copolymers. The addition of a small amount of GLN could effectively increase the swelling of the semi-IPNs in water. By employing the GLN-containing semi-IPN as a model system, the solvent/matrix interactions were demonstrated to reveal the effect of solvent structure on the swelling-shrinkage response. The addition of GLN improved the pH-sensitivity of the semi-IPN gels, resulting in a clear response to pH change by action of NH3+ and COOH of GLN and additional COOH groups from ITA. The mechanical performance of the copolymer network was improved by entangling PAAm/ITA chains with GLN, which acted as a reinforcement node. In terms of the effect of Hofmeister anions on the swelling behavior, the anion effect became more pronounced with salt concentration. The affinity of semi-IPNs towards the cationic dyes methylene blue and malachite green was tested and the dependence of the adsorption process on the initial dye concentration, contact time and GLN content was determined. This method presents a simple and efficient approach for the design of chemically crosslinked protein-based gels for drug delivery applications.


Assuntos
Gelatina , Polímeros , Acrilamidas , Aminas , Ânions , Corantes , Elasticidade , Gelatina/química , Hidrogéis/química , Azul de Metileno , Polímeros/química , Solventes , Succinatos , Água
17.
Proc Natl Acad Sci U S A ; 119(32): e2204453119, 2022 08 09.
Artigo em Inglês | MEDLINE | ID: mdl-35914159

RESUMO

Changes in the geometry and topology of self-assembled membranes underlie diverse processes across cellular biology and engineering. Similar to lipid bilayers, monolayer colloidal membranes have in-plane fluid-like dynamics and out-of-plane bending elasticity. Their open edges and micrometer-length scale provide a tractable system to study the equilibrium energetics and dynamic pathways of membrane assembly and reconfiguration. Here, we find that doping colloidal membranes with short miscible rods transforms disk-shaped membranes into saddle-shaped surfaces with complex edge structures. The saddle-shaped membranes are well approximated by Enneper's minimal surfaces. Theoretical modeling demonstrates that their formation is driven by increasing the positive Gaussian modulus, which in turn, is controlled by the fraction of short rods. Further coalescence of saddle-shaped surfaces leads to diverse topologically distinct structures, including shapes similar to catenoids, trinoids, four-noids, and higher-order structures. At long timescales, we observe the formation of a system-spanning, sponge-like phase. The unique features of colloidal membranes reveal the topological transformations that accompany coalescence pathways in real time. We enhance the functionality of these membranes by making their shape responsive to external stimuli. Our results demonstrate a pathway toward control of thin elastic sheets' shape and topology-a pathway driven by the emergent elasticity induced by compositional heterogeneity.


Assuntos
Bicamadas Lipídicas , Elasticidade , Bicamadas Lipídicas/química , Membranas/metabolismo , Distribuição Normal
18.
Philos Trans A Math Phys Eng Sci ; 380(2234): 20210331, 2022 Oct 17.
Artigo em Inglês | MEDLINE | ID: mdl-36031836

RESUMO

The conditions for bifurcation of a circular cylindrical tube of elastic material subjected to combined axial loading and internal pressure are well known and are frequently used as a reference in related works. The present paper takes the theory further by considering a residually stressed circular cylindrical dielectric tube subjected to a combination of internal or external pressure, axial load and radial electric field. We examine axisymmetric incremental deformations and increments in the electric displacement superimposed on a known finitely deformed and residually stressed configuration in the presence of an electric field. The governing equations and boundary conditions are first obtained in general form and then specialized for the neo-Hookean and Ogden electroelastic models. The system of equations is solved numerically for different values of charge density and radial and circumferential residual stresses, and the results are compared with the purely elastic case. The bifurcation curves are presented as the azimuthal stretch on the inner surface versus the axial stretch together with the corresponding zero pressure curves. This article is part of the theme issue 'The Ogden model of rubber mechanics: Fifty years of impact on nonlinear elasticity'.


Assuntos
Elasticidade
19.
Philos Trans A Math Phys Eng Sci ; 380(2234): 20210365, 2022 Oct 17.
Artigo em Inglês | MEDLINE | ID: mdl-36031838

RESUMO

Constitutive models are important to biomechanics for two key reasons. First, constitutive modelling is an essential component of characterizing tissues' mechanical properties for informing theoretical and computational models of biomechanical systems. Second, constitutive models can be used as a theoretical framework for extracting and comparing key quantities of interest from material characterization experiments. Over the past five decades, the Ogden model has emerged as a popular constitutive model in soft tissue biomechanics with relevance to both informing theoretical and computational models and to comparing material characterization experiments. The goal of this short review is threefold. First, we will discuss the broad relevance of the Ogden model to soft tissue biomechanics and the general characteristics of soft tissues that are suitable for approximating with the Ogden model. Second, we will highlight exemplary uses of the Ogden model in brain tissue, blood clot and other tissues. Finally, we offer a tutorial on fitting the one-term Ogden model to pure shear experimental data via both an analytical approximation of homogeneous deformation and a finite-element model of the tissue domain. Overall, we anticipate that this short review will serve as a practical introduction to the use of the Ogden model in biomechanics. This article is part of the theme issue 'The Ogden model of rubber mechanics: Fifty years of impact on nonlinear elasticity'.


Assuntos
Encéfalo , Modelos Biológicos , Fenômenos Biomecânicos , Elasticidade , Análise de Elementos Finitos , Estresse Mecânico
20.
Philos Trans A Math Phys Eng Sci ; 380(2234): 20210321, 2022 Oct 17.
Artigo em Inglês | MEDLINE | ID: mdl-36031840

RESUMO

Benign and malignant lesions in tissues or organs can be detected by elastographic investigations in which pathological regions are spotted from local alterations of the stiffness. As is known, the shear modulus provides a measure of the stiffness of an elastic material. Based on the classical theory of linear elasticity, an elastogram yields estimations of the linear shear modulus from measurements of the speed of small-amplitude transverse waves propagating in the medium tested. In this paper, we show that the estimation of the shear modulus can be improved significantly by employing the fourth-order weakly nonlinear theory of elasticity (FOE), and indicate how the stiffness can be assessed more precisely with the use of FOE. We discuss also why FOE provides more reliable results than the fully nonlinear theory of elasticity. This article is part of the theme issue 'The Ogden model of rubber mechanics: Fifty years of impact on nonlinear elasticity'.


Assuntos
Técnicas de Imagem por Elasticidade , Dinâmica não Linear , Módulo de Elasticidade , Elasticidade
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