Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 37.170
Filtrar
1.
BMC Health Serv Res ; 22(1): 618, 2022 May 09.
Artículo en Inglés | MEDLINE | ID: mdl-35534891

RESUMEN

BACKGROUND: Since 1993, Colombia has had a mandatory social health insurance scheme that aims to provide universal health coverage to all citizens. However, some contributory regime participants purchase voluntary private health insurance (VPHI) to access better quality health services (i. e., physicians and hospitals), shorter waiting times, and a more extensive providers' network. This article aims to estimate the price elasticity of demand for the VPHI market in Colombia. METHODS: We use data from the 2016-2017 consumer expenditure national survey and apply a Heckman selection model to address the selection problem into purchasing private insurance. Using the estimation results to further estimate the price semi-elasticity for VPHI, we then calculate the price elasticity for the households' health expenditure and acquisition of VHPI. RESULTS: Our main findings indicate that a 1% VPHI price increase reduces the proportion of households affiliated to a VPHI in the country by about 2.32% to 4.66%, with robust results across sample restrictions. There are relevant differences across age groups, with younger households' heads being less responsive to VPHI price changes. CONCLUSIONS: We conclude that the VPHI demand in Colombia is noticeably elastic, and therefore tax policy changes can have a significant impact on public health insurance expenditures. The government should estimate the optimal VPHI purchase in order to reduce any welfare loss that the current arrangement might be generating.


Asunto(s)
Seguro de Salud , Cobertura Universal del Seguro de Salud , Colombia , Elasticidad , Gastos en Salud , Humanos
2.
Adv Exp Med Biol ; 1364: 253-277, 2022.
Artículo en Inglés | MEDLINE | ID: mdl-35508879

RESUMEN

Resonant Ultrasound Spectroscopy estimates the stiffness coefficients of a material from the free resonant frequencies of a single specimen. It is particularly suitable for complete stiffness characterization of anisotropic materials available only as small samples (typically a few mm), and it does not suffer from some limitations associated to quasi-static mechanical test and ultrasound wave velocity measurements. RUS has been used for decades on geological samples and single crystals, but was until recently not applied to mineralized tissues such as bone. The reason is the significant mechanical damping presents in these materials, which causes the resonant peaks to overlap and prevent a direct measurement of the resonant frequencies. This chapter describes the use of RUS for the elastic characterization of mineralized tissues, cortical bone in particular. All steps are described, from sample preparation and measurement setup to signal processing and data analysis, including the developments and adaptions necessary to overcome the difficulties linked to damping. Viscoelastic characterization, from the width of the resonant peaks, is also presented. Mostly technical aspects are developed in this chapter, while the data obtained from RUS on several collections of mineralized tissues specimens are presented and discussed in Chap. 13.


Asunto(s)
Huesos , Hueso Cortical , Huesos/diagnóstico por imagen , Hueso Cortical/diagnóstico por imagen , Elasticidad , Análisis Espectral/métodos , Ultrasonografía
3.
Adv Exp Med Biol ; 1364: 279-295, 2022.
Artículo en Inglés | MEDLINE | ID: mdl-35508880

RESUMEN

Recent advances in resonant ultrasound spectroscopy (RUS) leverage accurate measurements of the anisotropic stiffness of hard tissues at millimeter scale. RUS is the only available technique to date to assess the entire stiffness tensor of bone from a unique rectangular parallelepiped specimen. Accurately measured stiffness constants are required for bone mechanics models and may provide information on some fundamental aspects of hard tissues biology such as regulation of bone mass, remodeling and healing. In this chapter, we review the anisotropic stiffness data of human hard tissues measured with RUS, mostly during the last decade. Hard tissues covered here include human enamel and dentin, cortical bone from the femur and tibia of human adults, and child cortical bone tissue, accounting for 288 specimens in total. Data was collected in the literature and from previous works of our group. We performed a comparative study to depict the differences in the elastic properties of these hard tissues. Our objectives were to: (1) document the range of anisotropic stiffness constants in human hard tissues (orthotropic or transverse isotropic symmetry); and (2) provide empirical laws between mass density and anisotropic stiffness of cortical bone at different skeletal sites. Finally, we discuss the challenges and perspectives to use RUS for large collections of specimens.


Asunto(s)
Hueso Cortical , Fémur , Adulto , Anisotropía , Niño , Elasticidad , Fémur/diagnóstico por imagen , Humanos , Análisis Espectral/métodos
4.
Adv Exp Med Biol ; 1364: 297-318, 2022.
Artículo en Inglés | MEDLINE | ID: mdl-35508881

RESUMEN

A better understanding of the mechanical behaviour of child bone is essential to improve the diagnosis of pediatric bone disorders that may influence bone development. Even though the process of bone growth is well described, there are still lacks of knowledge on intrinsic material properties of child bone and particularly on child bone considered as "non-pathological". Geometry, material properties, microstructure and biochemical components are associated with child bone fragility and remain difficult to assess for two main reasons: the scarcity of the bone samples and their small dimensions. In this context, ultrasonic methods offer interesting possibilities by exploiting in particular their non-destructive character. In this chapter, the elasticity properties of Non Pathological Child Cortical Bone (NPCCB) obtained by ultrasonic methods are presented. The objective was to contribute to the construction of a reference database on NPCCB that would serve as a point of comparison for analyzing the effect of a pathology or treatment. After the presentation of the hypotheses on the elasticity and anisotropy of NPCCB, ultrasonic transmission-mode and resonance spectroscopy methods are described. Results are presented and discussed with respect to microstructural and biochemical properties.


Asunto(s)
Huesos , Hueso Cortical , Anisotropía , Desarrollo Óseo , Huesos/diagnóstico por imagen , Niño , Hueso Cortical/diagnóstico por imagen , Elasticidad , Humanos
6.
J Bodyw Mov Ther ; 30: 176-180, 2022 Apr.
Artículo en Inglés | MEDLINE | ID: mdl-35500968

RESUMEN

The claim that the effects of kinesiology tape are different depending on the direction of tape application needs to be clearly ascertained. This study aimed to determine the immediate effects of two forearm kinesiology tape applications on muscle tone, stiffness, and elasticity of young individuals. Thirty-nine participants (15 men and 24 women) were randomized (1:1:1) to: the facilitatory group, receiving kinesiology tape applied from origin to insertion; the inhibitory group, receiving kinesiology tape applied from insertion to origin; or, a control group, without any intervention. The mechanical properties - tone, elasticity, and stiffness - of the forearm muscles were measured with a handheld mechanical impulse-based myotonometric device before and 30 min after the kinesiology tape application. Only the application of kinesiology tape from origin to insertion significantly increased muscle tone [16.6 (2.5) to 17.4 (3.5) Hz, p = 0.036], stiffness [318.3 (52) to 355.0 (87) N/m, p = 0.004], and elasticity [0.98 (0.1) to 1.10 (0.1), p = 0.023]. No changes were observed in both inhibitory kinesiology tape and the control group. In conclusion, kinesiology tape application has different effects depending on the direction of the taping application. The facilitatory tapping increased muscle tone, elasticity, and stiffness.


Asunto(s)
Cinta Atlética , Elasticidad , Femenino , Humanos , Masculino , Tono Muscular , Músculo Esquelético
7.
Front Endocrinol (Lausanne) ; 13: 872153, 2022.
Artículo en Inglés | MEDLINE | ID: mdl-35527993

RESUMEN

BRAFV600E is the most common mutated gene in thyroid cancer and is most closely related to papillary thyroid carcinoma(PTC). We investigated the value of elasticity and grayscale ultrasonography for predicting BRAFV600E mutations in PTC. Methods: 138 patients with PTC who underwent preoperative ultrasound between January 2014 and 2021 were retrospectively examined. Patients were divided into BRAFV600E mutation-free group (n=75) and BRAFV600E mutation group (n=63). Patients were randomly divided into training (n=96) and test (n=42) groups. A total of 479 radiomic features were extracted from the grayscale and elasticity ultra-sonograms. Regression analysis was done to select the features that provided the most information. Then, 10-fold cross-validation was used to compare the performance of different classification algorithms. Logistic regression was used to predict BRAFV600E mutations. Results: Eight radiomics features were extracted from the grayscale ultrasonogram, and five radiomics features were extracted from the elasticity ultrasonogram. Three models were developed using these radiomic features. The models were derived from elasticity ultrasound, grayscale ultrasound, and a combination of grayscale and elasticity ultrasound, with areas under the curve (AUC) 0.952 [95% confidence interval (CI), 0.914-0.990], AUC 0.792 [95% CI, 0.703-0.882], and AUC 0.985 [95% CI, 0.965-1.000] in the training dataset, AUC 0.931 [95% CI, 0.841-1.000], AUC 0. 725 [95% CI, 0.569-0.880], and AUC 0.938 [95% CI, 0.851-1.000] in the test dataset, respectively. Conclusion: The radiomic model based on grayscale and elasticity ultrasound had a good predictive value for BRAFV600E gene mutations in patients with PTC.


Asunto(s)
Proteínas Proto-Oncogénicas B-raf , Neoplasias de la Tiroides , Elasticidad , Humanos , Mutación , Proteínas Proto-Oncogénicas B-raf/genética , Estudios Retrospectivos , Cáncer Papilar Tiroideo/diagnóstico por imagen , Cáncer Papilar Tiroideo/genética , Cáncer Papilar Tiroideo/patología , Neoplasias de la Tiroides/diagnóstico por imagen , Neoplasias de la Tiroides/genética , Neoplasias de la Tiroides/patología , Ultrasonografía
8.
J Refract Surg ; 38(5): 318-325, 2022 May.
Artículo en Inglés | MEDLINE | ID: mdl-35536713

RESUMEN

PURPOSE: To determine the effectiveness of parameters and indices based on biomechanical measures at discriminating fellow eyes with topographically and tomographically normal corneas in patients with keratoconus from normal control corneas. METHODS: The study included 47 keratoconus suspect eyes, defined as the topographically and tomographically normal fellow eyes of patients with frank keratoconus in the other eye. Eyes were imaged using the Pentacam HR and Corvis ST (both Oculus Optikgeräte GmbH). Fellow eyes were then categorized as topographically/tomographically normal fellow eyes (TNF) and topographically/tomographically borderline fellow eyes (TBF). The ability of each of the Corvis Biomechanical Index (CBI), Tomographic and Biomechanical Index (TBI), stiffness parameter at applanation 1 (SP-A1), and stress-strain index (SSI) at discriminating between normal controls and keratoconus suspects was assessed. RESULTS: The TBI had the best discriminative ability with the greatest area under the receiver operating characteristic (AUROC) curve value of 0.946 for normal controls versus TBF eyes, and 0.824 for normal controls versus TNF eyes. Compared to the TBI AUROC curves, SP-A1 and CBI had AUROC curve values of 0.833 (P = .09) and 0.822 (P = .01) for normal controls versus TBF eyes, respectively, and AUROC curve values of 0.822 (P = .96) and 0.550 (P = .0002) for normal controls versus TNF eyes, respectively. The TBI had the best positive predictive value for TNF and TBF eyes, followed by CBI and SP-A1. CONCLUSIONS: The TBI and the purely biomechanical parameter SP-A1 were of moderate utility in distinguishing between normal and keratoconus suspect eyes. In the absence of topographic/tomographic evidence of keratectasia, an independently abnormal biomechanical parameter may suggest an increased risk of ectasia. [J Refract Surg. 2022;38(5):318-325.].


Asunto(s)
Queratocono , Fenómenos Biomecánicos , Córnea/diagnóstico por imagen , Paquimetría Corneal/métodos , Topografía de la Córnea/métodos , Elasticidad , Humanos , Queratocono/diagnóstico , Curva ROC , Estudios Retrospectivos
9.
Zhongguo Zhong Yao Za Zhi ; 47(8): 2244-2250, 2022 Apr.
Artículo en Chino | MEDLINE | ID: mdl-35531741

RESUMEN

The present study explored the correlation of coronary heart disease(CHD) with blood stasis syndrome in postmenopausal women with artery elasticity and endothelial function indexes and evaluated the diagnostic efficacy of the prediction model via logistic regression and receiver operating characteristic(ROC) curve model. A retrospective comparison was made between 366 postmenopausal CHD patients from August 1, 2020, to September 30, 2021, in the Department of Cardiology of Integrated Traditional Chinese and Western Medicine of China-Japan Friendship Hospital, who were divided into the blood stasis syndrome group(n=196) and the non-blood stasis syndrome group(n=170). General clinical characteristics of the two groups were compared. Multivariate logistic regression analysis was used to probe the correlation of CHD with blood stasis syndrome in postmenopausal women with brachial-ankle pulse wave velocity(baPWV), ankle-brachial index(ABI), and flow-mediated dilatation(FMD), and the ROC curve was drawn to evaluate the diagnostic efficiency of the prediction model. Multivariate logistic regression analysis showed that the correlation coefficients of CHD with blood stasis syndrome in postmenopausal women with baPWV, ABI, and FMD were 1.123, 0.109, and 0.719, respectively(P=0.004, P=0.005, P<0.001),and the regression equation for predicting probability P was P=1/[1+e~(-(3.131+0.116×baPWV-2.217×ABI-0.330×FMD))]. ROC curve analysis suggested that in the context of baPWV≥19.19 m·s~(-1) or ABI≤1.22 or FMD≤9.7%, it was of great significance to predict the diagnosis of CHD with blood stasis syndrome in postmenopausal women. The AUC of baPWV, ABI, FMD, and prediction probability P was 0.763, 0.607, 0.705, and 0.836, respectively. The AUC of prediction probability P was higher than that of each index alone(P<0.001), and the sensitivity and specificity were 0.888 and 0.647, respectively. The results demonstrate that baPWV, ABI, and FMD are independently correlated with CHD with blood stasis syndrome in postmenopausal women, and show certain independent predictive abilities(P<0.05). The combined evaluation of the three possesses the best diagnostic efficiency.


Asunto(s)
Índice Tobillo Braquial , Enfermedad Coronaria , Arteria Braquial , Enfermedad Coronaria/diagnóstico , Elasticidad , Femenino , Humanos , Modelos Logísticos , Posmenopausia , Análisis de la Onda del Pulso , Curva ROC , Estudios Retrospectivos
10.
Redox Biol ; 52: 102306, 2022 06.
Artículo en Inglés | MEDLINE | ID: mdl-35367810

RESUMEN

Titin, as the main protein responsible for the passive stiffness of the sarcomere, plays a key role in diastolic function and is a determinant factor in the etiology of heart disease. Titin stiffness depends on unfolding and folding transitions of immunoglobulin-like (Ig) domains of the I-band, and recent studies have shown that oxidative modifications of cryptic cysteines belonging to these Ig domains modulate their mechanical properties in vitro. However, the relevance of this mode of titin mechanical modulation in vivo remains largely unknown. Here, we describe the high evolutionary conservation of titin mechanical cysteines and show that they are remarkably oxidized in murine cardiac tissue. Mass spectrometry analyses indicate a similar landscape of basal oxidation in murine and human myocardium. Monte Carlo simulations illustrate how disulfides and S-thiolations on these cysteines increase the dynamics of the protein at physiological forces, while enabling load- and isoform-dependent regulation of titin stiffness. Our results demonstrate the role of conserved cysteines in the modulation of titin mechanical properties in vivo and point to potential redox-based pathomechanisms in heart disease.


Asunto(s)
Cardiopatías , Sarcómeros , Animales , Conectina/química , Cisteína/metabolismo , Elasticidad , Cardiopatías/metabolismo , Humanos , Ratones , Miocardio/metabolismo , Oxidación-Reducción , Proteínas Quinasas/genética , Proteínas Quinasas/metabolismo , Sarcómeros/metabolismo
11.
Int J Mol Sci ; 23(7)2022 Mar 23.
Artículo en Inglés | MEDLINE | ID: mdl-35408861

RESUMEN

Lipid domains less than 200 nm in size may form a scaffold, enabling the concerted function of plasma membrane proteins. The size-regulating mechanism is under debate. We tested the hypotheses that large values of spontaneous monolayer curvature are incompatible with micrometer-sized domains. Here, we used the transition of photoswitchable lipids from their cylindrical conformation to a conical conformation to increase the negative curvature of a bilayer-forming lipid mixture. In contrast to the hypothesis, pre-existing micrometer-sized domains did not dissipate in our planar bilayers, as indicated by fluorescence images and domain mobility measurements. Elasticity theory supports the observation by predicting the zero free energy gain for splitting large domains into smaller ones. It also indicates an alternative size-determining mechanism: The cone-shaped photolipids reduce the line tension associated with lipid deformations at the phase boundary and thus slow down the kinetics of domain fusion. The competing influence of two approaching domains on the deformation of the intervening lipids is responsible for the kinetic fusion trap. Our experiments indicate that the resulting local energy barrier may restrict the domain size in a dynamic system.


Asunto(s)
Membrana Dobles de Lípidos , Modelos Químicos , Elasticidad , Cinética , Conformación Molecular
12.
J Mech Behav Biomed Mater ; 130: 105204, 2022 Jun.
Artículo en Inglés | MEDLINE | ID: mdl-35367687

RESUMEN

This study focuses on the variations in the brain tissue dynamic behaviour pointing out new insight into the material nonlinear viscoelasticity. Shear dynamic response curves are obtained in different working conditions in terms of strain sweep and superimposed static compression offsets (SCO) applied in orthogonal direction to the shear. The strain sweep mode is used to study the storage and loss moduli dependence on the amplitude of the applied strain. It is found that the material exhibits linear viscoelastic behaviour up to about 0.1% strain amplitude. Above this critical threshold, the storage modulus G' decreases rapidly with increasing dynamic strain amplitude and this effect is gradually intensified as the SCO are increased. In addition, it is observed that the loss factor (G''/G') increases by increasing the SCO applied to the specimens. The dynamic strain amplitude results of the storage modulus reveal that the elastic component of the brain tissue's stiffness (G') evaluated at low strain strongly increases with increasing static superimposed compression strain while the loss factor in the same strain range appears to be SCO independent. Finally, dynamic stiffness recovery after a large strain deformation is considered. The reduction in low amplitude dynamic modulus and subsequent recovery kinetics due to a perturbation is found to be independent of the level of the SCO. The same assessments were carried out on 5 consecutive strain sweep cycle loading. It has been noticed that at the last cycle, the dissipation peak is reduced, and the non-linearity of the curve begins earlier. This could be explained by the effects of cerebral edema on cells and their surrounding environment.


Asunto(s)
Encéfalo , Dinámicas no Lineales , Elasticidad , Humanos , Cinética , Estrés Mecánico , Viscosidad
13.
J R Soc Interface ; 19(189): 20220050, 2022 Apr.
Artículo en Inglés | MEDLINE | ID: mdl-35382580

RESUMEN

Reversible and switchable adhesion of elastomeric microstructures has attracted significant interest in the development of grippers for object manipulation. Their applications, however, have often been limited to dry conditions and adhesion of such deformable microfibrils in the fluid environment is less understood. In the present study, we performed adhesion tests in silicone oil using single cylindrical microfibrils of a flat-punch shape with a radius of 80 µm. Stiff fibrils were created using three-dimensional printing of an elastomeric resin with an elastic modulus of 500 MPa, and soft fibrils, with a modulus of 3.3 MPa, were moulded in polyurethane. Our results suggest that adhesion is dominated by hydrodynamic forces, which can be maximized by stiff materials and high retraction velocities, in line with theoretical predictions. The maximum pull-off stress of stiff cylindrical fibrils is 0.6 MPa, limited by cavitation and viscous fingering, occurring at retraction velocities greater than 2 µm s-1. Next, we add a mushroom cap to the microfibrils, which, in the case of the softer material, deforms upon retraction and leads to a transition to a hydrostatic suction regime with higher pull-off stresses ranging from 0.7 to 0.9 MPa. The effects of elastic modulus, fibril size and viscosity for underwater applications are illustrated in a mechanism map to provide guidance for design optimization.


Asunto(s)
Hidrodinámica , Microfibrillas , Módulo de Elasticidad , Elasticidad , Viscosidad
14.
J Mech Behav Biomed Mater ; 130: 105186, 2022 Jun.
Artículo en Inglés | MEDLINE | ID: mdl-35405520

RESUMEN

Parameterized cellular microstructures allow for the development of efficient multiscale optimization strategies for the design of Functionally Graded Scaffolds (FGSs). This work assesses the biomimetic capabilities of the Voronoi-based cancelous bone microstructure introduced by Fantini et al. (2016) in terms of histomorphometric and elastic properties. Histomorphometric data of 23 bovine bone specimens and elastic data of 140 human bone specimens are used as reference. Based on the key findings that there exists a strong correspondence between the trabecular thickness and the solid volume fraction for natural cancelous bone, and that the stretching of the Voronoi microstructure is an effective means to induce anisotropy, the generative procedure by Fantini et al. (2016) is assessed and tuned to account for anisotropy and elastic properties. It is shown that the resulting mimetic microstructures have histomorphometric features and elastic properties that are in very good accordance to those of the natural samples. The outcomes of this work are a step forward towards the integration of the Voronoi-based microstructure into multiscale design tools.


Asunto(s)
Biomimética , Huesos , Animales , Anisotropía , Bovinos , Elasticidad , Humanos
15.
Commun Biol ; 5(1): 402, 2022 04 29.
Artículo en Inglés | MEDLINE | ID: mdl-35488088

RESUMEN

Material properties of living matter play an important role for biological function and development. Yet, quantification of material properties of internal organs in vivo, without causing physiological damage, remains challenging. Here, we present a non-invasive approach based on modified optical tweezers for quantifying sub-cellular material properties deep inside living zebrafish embryos. Material properties of cells within the foregut region are quantified as deep as 150 µm into the biological tissue through measurements of the positions of an inert tracer. This yields an exponent, α, which characterizes the scaling behavior of the positional power spectra and the complex shear moduli. The measurements demonstrate differential mechanical properties: at the time when the developing organs undergo substantial displacements during morphogenesis, gut progenitors are more elastic (α = 0.57 ± 0.07) than the neighboring yolk (α = 0.73 ± 0.08), liver (α = 0.66 ± 0.06) and two mesodermal (α = 0.68 ± 0.06, α = 0.64 ± 0.06) progenitor cell populations. The higher elasticity of gut progenitors correlates with an increased cellular concentration of microtubules. The results infer a role of material properties during morphogenesis and the approach paves the way for quantitative material investigations in vivo of embryos, explants, or organoids.


Asunto(s)
Endodermo , Pez Cebra , Animales , Elasticidad , Hígado , Morfogénesis
16.
Biophys J ; 121(9): 1632-1642, 2022 May 03.
Artículo en Inglés | MEDLINE | ID: mdl-35390297

RESUMEN

Cell viscoelastic properties are affected by the cell cycle, differentiation, and pathological processes such as malignant transformation. Therefore, evaluation of the mechanical properties of the cells proved to be an approach to obtaining information on the functional state of the cells. Most of the currently used methods for cell mechanophenotyping are limited by low robustness or the need for highly expert operation. In this paper, the system and method for viscoelasticity measurement using shear stress induction by fluid flow is described and tested. Quantitative phase imaging (QPI) is used for image acquisition because this technique enables one to quantify optical path length delays introduced by the sample, thus providing a label-free objective measure of morphology and dynamics. Viscosity and elasticity determination were refined using a new approach based on the linear system model and parametric deconvolution. The proposed method allows high-throughput measurements during live-cell experiments and even through a time lapse, whereby we demonstrated the possibility of simultaneous extraction of shear modulus, viscosity, cell morphology, and QPI-derived cell parameters such as circularity or cell mass. Additionally, the proposed method provides a simple approach to measure cell refractive index with the same setup, which is required for reliable cell height measurement with QPI, an essential parameter for viscoelasticity calculation. Reliability of the proposed viscoelasticity measurement system was tested in several experiments including cell types of different Young/shear modulus and treatment with cytochalasin D or docetaxel, and an agreement with atomic force microscopy was observed. The applicability of the proposed approach was also confirmed by a time-lapse experiment with cytochalasin D washout, whereby an increase of stiffness corresponded to actin repolymerization in time.


Asunto(s)
Neoplasias , Citocalasina D , Módulo de Elasticidad , Elasticidad , Reproducibilidad de los Resultados , Viscosidad
17.
J Vis Exp ; (181)2022 03 25.
Artículo en Inglés | MEDLINE | ID: mdl-35404355

RESUMEN

The viscoelastic properties of erythrocytes have been investigated by a range of techniques. However, the reported experimental data vary. This is not only attributed to the normal variability of cells, but also to the differences in methods and models of cell response. Here, an integrated protocol using optical tweezers and defocusing microscopy is employed to obtain the rheological features of red blood cells in the frequency range of 1 Hz to 35 Hz. While optical tweezers are utilized to measure the erythrocyte-complex elastic constant, defocusing microscopy is able to obtain the cell height profile, volume, and its form factor a parameter that allows conversion of complex elastic constant into complex shear modulus. Moreover, applying a soft glassy rheology model, the scaling exponent for both moduli can be obtained. The developed methodology allows to explore the mechanical behavior of red blood cells, characterizing their viscoelastic parameters, obtained under well-defined experimental conditions, for several physiological and pathological conditions.


Asunto(s)
Microscopía , Pinzas Ópticas , Elasticidad , Eritrocitos/patología , Proyectos de Investigación , Reología/métodos , Viscosidad
18.
J Acoust Soc Am ; 151(4): 2403, 2022 Apr.
Artículo en Inglés | MEDLINE | ID: mdl-35461517

RESUMEN

Dynamic elastography, whether based on magnetic resonance, ultrasound, or optical modalities, attempts to reconstruct quantitative maps of the viscoelastic properties of biological tissue, properties that are altered by disease and injury, by noninvasively measuring mechanical wave motion in the tissue. Most reconstruction strategies that have been developed neglect boundary conditions, including quasistatic tensile or compressive loading resulting in a nonzero prestress. Significant prestress is inherent to the functional role of some biological tissues currently being studied using elastography, such as skeletal and cardiac muscle, arterial walls, and the cornea. In the present article, we review how prestress alters both bulk mechanical wave motion and wave motion in one- and two-dimensional waveguides. Key findings are linked to studies on skeletal muscle and the human cornea, as one- and two-dimensional waveguide examples. This study highlights the underappreciated combined acoustoelastic and waveguide challenge to elastography. Can elastography truly determine viscoelastic properties of a material when what it is measuring is affected by both these material properties and unknown prestress and other boundary conditions?


Asunto(s)
Diagnóstico por Imagen de Elasticidad , Anisotropía , Elasticidad , Diagnóstico por Imagen de Elasticidad/métodos , Humanos , Imagen por Resonancia Magnética , Movimiento (Física) , Ultrasonografía
19.
PLoS One ; 17(4): e0266235, 2022.
Artículo en Inglés | MEDLINE | ID: mdl-35385536

RESUMEN

Temporal variations of the extracellular matrix (ECM) stiffness profoundly impact cellular behaviors, possibly more significantly than the influence of static stiffness. Three-dimensional (3D) cell cultures with tunable matrix stiffness have been utilized to characterize the mechanobiological interactions of elasticity-mediated cellular behaviors. Conventional studies usually perform static interrogations of elasticity at micro-scale resolution. While such studies are essential for investigations of cellular mechanotransduction, few tools are available for depicting the temporal dynamics of the stiffness of the cellular environment, especially for optically turbid millimeter-sized biomaterials. We present a single-element transducer shear wave (SW) elasticity imaging system that is applied to a millimeter-sized, ECM-based cell-laden hydrogel. The single-element ultrasound transducer is used both to generate SWs and to detect their arrival times after being reflected from the side boundaries of the sample. The sample's shear wave speed (SWS) is calculated by applying a time-of-flight algorithm to the reflected SWs. We use this noninvasive and technically straightforward approach to demonstrate that exposing 3D cancer cell cultures to X-ray irradiation induces a temporal change in the SWS. The proposed platform is appropriate for investigating in vitro how a group of cells remodels their surrounding matrix and how changes to their mechanical properties could affect the embedded cells in optically turbid millimeter-sized biomaterials.


Asunto(s)
Diagnóstico por Imagen de Elasticidad , Materiales Biocompatibles , Elasticidad , Diagnóstico por Imagen de Elasticidad/métodos , Mecanotransducción Celular , Fantasmas de Imagen , Transductores
20.
J Mech Behav Biomed Mater ; 130: 105178, 2022 Jun.
Artículo en Inglés | MEDLINE | ID: mdl-35364365

RESUMEN

The Autoprogressive (AutoP) method is a data-driven inverse method that leverages finite element analysis (FEA) and machine learning (ML) techniques to build constitutive relationships from measured force and displacement data. Previous applications of AutoP in tissue-like media have focused on linear elastic mechanical behavior as the target object is infinitesimally compressed. In this study, we extended the application of AutoP in characterizing nonlinear elastic mechanical behavior as the target object undergoes finite compressive deformation. Guided by the prior of nonlinear media, we modified the training data generated by AutoP to speed its ability to learn to model deformations. AutoP training was validated using both synthetic and experimental data recorded from 3D objects. Force-displacement measurements were obtained using ultrasonic imaging from heterogeneous agar-gelatin phantoms. Measurement on samples of phantom components were analyzed to obtain independent measurements of material properties. Comparisons validated the material properties found from neural network constitutive models (NNCMs) trained using AutoP. Results were found to be robust to measurement errors and spatial variations in material properties.


Asunto(s)
Redes Neurales de la Computación , Dinámicas no Lineales , Agar , Elasticidad , Análisis de Elementos Finitos , Modelos Biológicos , Fantasmas de Imagen , Estrés Mecánico
SELECCIÓN DE REFERENCIAS
DETALLE DE LA BÚSQUEDA
...