Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 65.594
Filtrar
1.
Proc Biol Sci ; 287(1931): 20201410, 2020 07 29.
Artículo en Inglés | MEDLINE | ID: mdl-33043862

RESUMEN

Joint friction has never previously been considered in the computation of mechanical and metabolic energy balance of human and animal (loco)motion, which heretofore included just muscle work to move the body centre of mass (external work) and body segments with respect to it. This happened mainly because, having been previously measured ex vivo, friction was considered to be almost negligible. Present evidences of in vivo damping of limb oscillations, motion captured and processed by a suited mathematical model, show that: (a) the time course is exponential, suggesting a viscous friction operated by the all biological tissues involved; (b) during the swing phase, upper limbs report a friction close to one-sixth of the lower limbs; (c) when lower limbs are loaded, in an upside-down body posture allowing to investigate the hip joint subjected to compressive forces as during the stance phase, friction is much higher and load dependent; and (d) the friction of the four limbs during locomotion leads to an additional internal work that is a remarkable fraction of the mechanical external work. These unprecedented results redefine the partitioning of the energy balance of locomotion, the internal work components, muscle and transmission efficiency, and potentially readjust the mechanical paradigm of the different gaits.


Asunto(s)
Extremidades , Articulaciones , Locomoción , Animales , Fricción , Humanos , Metabolismo , Estrés Mecánico
2.
Phys Rev Lett ; 125(12): 128103, 2020 Sep 18.
Artículo en Inglés | MEDLINE | ID: mdl-33016731

RESUMEN

While many cellular mechanisms leading to chemotherapeutic resistance have been identified, there is an increasing realization that tumor-stroma interactions also play an important role. In particular, mechanical alterations are inherent to solid cancer progression and profoundly impact cell physiology. Here, we explore the influence of compressive stress on the efficacy of chemotherapeutics in pancreatic cancer spheroids. We find that increased compressive stress leads to decreased drug efficacy. Theoretical modeling and experiments suggest that mechanical stress decreases cell proliferation which in turn reduces the efficacy of chemotherapeutics that target proliferating cells. Our work highlights a mechanical form of drug resistance and suggests new strategies for therapy.


Asunto(s)
Antineoplásicos/farmacología , Carcinoma Ductal Pancreático/tratamiento farmacológico , Carcinoma Ductal Pancreático/patología , Modelos Biológicos , Neoplasias Pancreáticas/tratamiento farmacológico , Neoplasias Pancreáticas/patología , Proliferación Celular/efectos de los fármacos , Proliferación Celular/fisiología , Desoxicitidina/análogos & derivados , Desoxicitidina/farmacología , Resistencia a Antineoplásicos , Humanos , Estrés Mecánico
3.
Dental Press J Orthod ; 25(4): 44-50, 2020.
Artículo en Inglés | MEDLINE | ID: mdl-32965386

RESUMEN

OBJECTIVE: To perform a numerical simulation using FEM to study the von Mises stresses on Mushroom archwires. METHODS: Mushroom archwires made of titanium-molybdenum alloy with 0.017 x 0.025-in cross-section were used in this study. A YS of 1240 MPa and a Young's modulus of 69 GPa were adopted. The archwire was modeled in Autodesk Inventor software and its behavior was simulated using the finite element code Ansys Workbench (Swanson Analysis Systems, Houston, Pennsylvania, USA). A large displacement simulation was used for non-linear analysis. The archwires were deformed in their extremities with 0° and 45°, and activated by their vertical extremities separated at 4.0 or 5.0 mm. RESULTS: Tensions revealed a maximum of 1158 MPa at the whole part of the loop at 5.0mm of activation, except in a very small area situated at the top of the loop, in which a maximum of 1324 Mpa was found. CONCLUSIONS: Mushroom loops are capable to produce tension levels in an elastic range and could be safely activated up to 5.0mm.


Asunto(s)
Agaricales , Incisivo , Fenómenos Biomecánicos , Módulo de Elasticidad , Análisis de Elementos Finitos , Estrés Mecánico
4.
Zhongguo Gu Shang ; 33(8): 766-70, 2020 Aug 25.
Artículo en Chino | MEDLINE | ID: mdl-32875770

RESUMEN

OBJECTIVE: To establish a 3D finite element model of normal knee joint involved its meniscus, which can be used to simulate the anatomical morphology and characteristics of human knee joint, to verify the validity of the model by preliminary FEA mechanical analysis, and explain partially biomechanical mechanisms of meniscus. METHODS: CT and MRI data were harvested by scanning the knee joint of a healthy male volunteer, and then these data were imported into Mimics 10.01 software and Geomagic Studio software to constructed the 3D models of tissue structures of knee joint. These models were combined to constructed the 3D model of intact knee joint and meshed in ANSA software. Therefore the finite element model of intact knee joint was established. Finally, after the definitionof its material behavior, boundary conditions and loading. The finite element model of knee joint was analyzed and verified using ANSYS software. Meanwhile The biomechanical properties of meniscus were analyzed. RESULTS: The complete knee finite element model composed of bone, meniscus, articular cartilage, and major ligaments was established. It could effectively simulate the anatomical morphology and characteristics of knee joint and its meniscus. The contact area of medial meniscus was 771.05 mm2, while the contact area of lateral meniscus was 634.31 mm2, and the ratio was 1.216. The stress distribution was uniform, but the stress of the medial meniscus was higher than that of the lateral meniscus, and the peak stress located in the posterior horn of the medial meniscus and the anterior horn of the lateral meniscus, respectively, and the peak stress value was 4.11 MPa. The maximum displacement of the meniscus was located in body, and the displacement of the medial meniscus was more remarkable than that of the lateral meniscus, and the maximum displacement value is 0.33 mm. The obtained finite element analysis results corresponded to that reported in the literature, which mean the model's reliability. CONCLUSION: The established finite element model of knee joint are proved to be have validity, and is a useful model for finite element analysis of meniscus tear and menisectomy. The results of finite element analysis can explain partially biomechanical mechanisms of meniscus which can provide theoretical guidance for clinical treatment of meniscus injury.


Asunto(s)
Menisco , Fenómenos Biomecánicos , Análisis de Elementos Finitos , Humanos , Articulación de la Rodilla , Masculino , Meniscos Tibiales , Reproducibilidad de los Resultados , Estrés Mecánico
5.
Int J Prosthodont ; 33(5): 523-526, 2020.
Artículo en Inglés | MEDLINE | ID: mdl-32956433

RESUMEN

PURPOSE: To investigate the three-point flexural strength of a novel CAD/CAM fiber-reinforced composite (FRC) material following different aging conditions. MATERIALS AND METHODS: The specimens were randomly assigned to one of five groups based on aging condition: (1) control (no treatment); (2) short-term water storage; (3) thermal degradation with autoclaving; (4) chemical degradation with hydrochloric acid; and (5) chemical degradation with citric acid (n = 10 per group). The specimens in the control group received no treatment. Following each treatment protocol, the three-point bending test was used to calculate the flexural strength. Data were statistically analyzed (α = .05), and scanning electron microscopy (SEM) analysis of the specimens was conducted. RESULTS: No significant differences in flexural strength were observed among the groups (P = .199). In addition, no distinct morphologic differences were detected in the SEM images of the specimens. CONCLUSION: The flexural strength of this novel CAD/CAM FRC material was unaffected by different aging methods.


Asunto(s)
Resinas Compuestas , Resistencia Flexional , Diseño Asistido por Computadora , Ensayo de Materiales , Microscopía Electrónica de Rastreo , Proyectos Piloto , Docilidad , Estrés Mecánico , Propiedades de Superficie
6.
J Cardiovasc Magn Reson ; 22(1): 67, 2020 09 10.
Artículo en Inglés | MEDLINE | ID: mdl-32912285

RESUMEN

BACKGROUND: The posterior wall of the proximal internal carotid artery (ICA) is the predilection site for the development of stenosis. To optimally prevent stroke, identification of new risk factors for plaque progression is of high interest. Therefore, we studied the impact of carotid geometry and wall shear stress on cardiovascular magnetic resonance (CMR)-depicted wall thickness in the ICA of patients with high cardiovascular disease risk. METHODS: One hundred twenty-one consecutive patients ≥50 years with hypertension, ≥1 additional cardiovascular risk factor and ICA plaque ≥1.5 mm thickness and < 50% stenosis were prospectively included. High-resolution 3D-multi-contrast (time of flight, T1, T2, proton density) and 4D flow CMR were performed for the assessment of morphological (bifurcation angle, ICA/common carotid artery (CCA) diameter ratio, tortuosity, and wall thickness) and hemodynamic parameters (absolute/systolic wall shear stress (WSS), oscillatory shear index (OSI)) in 242 carotid bifurcations. RESULTS: We found lower absolute/systolic WSS, higher OSI and increased wall thickness in the posterior compared to the anterior wall of the ICA bulb (p < 0.001), whereas this correlation disappeared in ≥10% stenosis. Higher carotid tortuosity (regression coefficient = 0.764; p < 0.001) and lower ICA/CCA diameter ratio (regression coefficient = - 0.302; p < 0.001) were independent predictors of increased wall thickness even after adjustment for cardiovascular risk factors. This association was not found for bifurcation angle, WSS or OSI in multivariate regression analysis. CONCLUSIONS: High carotid tortuosity and low ICA diameter were independent predictors for wall thickness of the ICA bulb in this cross-sectional study, whereas this association was not present for WSS or OSI. Thus, consideration of geometric parameters of the carotid bifurcation could be helpful to identify patients at increased risk of carotid plaque generation. However, this association and the potential benefit of WSS measurement need to be further explored in a longitudinal study.


Asunto(s)
Enfermedades de las Arterias Carótidas/diagnóstico por imagen , Arteria Carótida Interna/diagnóstico por imagen , Hemodinámica , Angiografía por Resonancia Magnética , Anciano , Enfermedades de las Arterias Carótidas/fisiopatología , Arteria Carótida Interna/fisiopatología , Estudios Transversales , Femenino , Humanos , Masculino , Persona de Mediana Edad , Placa Aterosclerótica , Valor Predictivo de las Pruebas , Pronóstico , Estudios Prospectivos , Flujo Sanguíneo Regional , Factores de Riesgo , Estrés Mecánico
7.
Nat Commun ; 11(1): 4828, 2020 09 24.
Artículo en Inglés | MEDLINE | ID: mdl-32973141

RESUMEN

ATR responds to mechanical stress at the nuclear envelope and mediates envelope-associated repair of aberrant topological DNA states. By combining microscopy, electron microscopic analysis, biophysical and in vivo models, we report that ATR-defective cells exhibit altered nuclear plasticity and YAP delocalization. When subjected to mechanical stress or undergoing interstitial migration, ATR-defective nuclei collapse accumulating nuclear envelope ruptures and perinuclear cGAS, which indicate loss of nuclear envelope integrity, and aberrant perinuclear chromatin status. ATR-defective cells also are defective in neuronal migration during development and in metastatic dissemination from circulating tumor cells. Our findings indicate that ATR ensures mechanical coupling of the cytoskeleton to the nuclear envelope and accompanying regulation of envelope-chromosome association. Thus the repertoire of ATR-regulated biological processes extends well beyond its canonical role in triggering biochemical implementation of the DNA damage response.


Asunto(s)
Proteínas de la Ataxia Telangiectasia Mutada/metabolismo , Núcleo Celular/metabolismo , Estrés Mecánico , Citoesqueleto de Actina , Animales , Proteínas de la Ataxia Telangiectasia Mutada/genética , Encéfalo , Cromatina , Citoplasma , Citoesqueleto/metabolismo , Daño del ADN , Ratones Noqueados , Metástasis de la Neoplasia , Neurogénesis , Membrana Nuclear/metabolismo
8.
Nan Fang Yi Ke Da Xue Xue Bao ; 40(6): 911-915, 2020 Jun 30.
Artículo en Chino | MEDLINE | ID: mdl-32895206

RESUMEN

OBJECTIVE: To analyze the biomechanics of cystic lesions in the mandibular body in a three-dimensional (3D) finite element model. METHODS: A 3D finite element model of cystic lesion of the mandibular body was constructed based on the CT images of the mandible of a healthy adult female volunteer with normal occlusion. The size of the cyst and the residual bone wall were analyzed when the lesion area approached the stress peak under certain constraints and loading conditions. RESULTS: When the size of the cyst reached 37.63 mm×11.32 mm×21.45 mm, the maximal von Mises stress in the lesion area reached 77.295 MPa, close to the yield strength of the mandible with a risk of pathological fracture. At this point, the remaining bone thickness of the buccal and lingual sides and the lower margin of the mandible in the lesion area was 1.52 mm, 0.76 mm and 1.04 mm, respectively. CONCLUSIONS: Residual bone mass is an important factor to affect the risk of pathological fracture after curettage of cystic lesions. A thickness as low as 1 mm of the residual bone cortex in the cystic lesion area of the mandibular body can be used as the threshold for a clinical decision on one-stage windowing decompression combined with two- stage curettage.


Asunto(s)
Imagenología Tridimensional , Mandíbula , Adulto , Fenómenos Biomecánicos , Femenino , Análisis de Elementos Finitos , Humanos , Estrés Mecánico
9.
J Oral Sci ; 62(4): 420-422, 2020 Sep 26.
Artículo en Inglés | MEDLINE | ID: mdl-32908079

RESUMEN

This study compared the mechanical properties and molecular distribution of a polymethyl methacrylate (PMMA) block (Dry) with specimens that were fabricated by a conventional method and cured in a wet environment (Control). Two specimen types were fabricated with heat-curing denture base resin. Dry specimens were polymerized at high pressure and in a dry system, while Control specimens were polymerized with a heat-curing method, in accordance with the manufacturer's recommended procedures. Specimens from each group were evaluated for three-point bending, water sorption and solubility, and color change, and by gel permeation chromatography (GPC). Mean values for the flexural strengths and moduli of the Dry specimens were significantly higher than those of the Control specimens (P > 0.05). Water sorption and discoloration values of the Dry group were significantly lower than those of the Control group. Mean weight-average molecular weights of the Dry group were higher than those of the Control group. As compared with the conventional method, the present method of fabricating PMMA blocks under high pressure yields superior mechanical properties for the denture base.


Asunto(s)
Diseño Asistido por Computadora , Polimetil Metacrilato , Bases para Dentadura , Dentaduras , Ensayo de Materiales , Estrés Mecánico , Propiedades de Superficie
10.
Nat Commun ; 11(1): 4902, 2020 09 29.
Artículo en Inglés | MEDLINE | ID: mdl-32994402

RESUMEN

Living cells and tissues experience various complex modes of forces that are important in physiology and disease. However, how different force modes impact gene expression is elusive. Here we apply local forces of different modes via a magnetic bead bound to the integrins on a cell and quantified cell stiffness, chromatin deformation, and DHFR (dihydrofolate reductase) gene transcription. In-plane stresses result in lower cell stiffness than out-of-plane stresses that lead to bead rolling along the cell long axis (i.e., alignment of actin stress fibers) or at different angles (90° or 45°). However, chromatin stretching and ensuing DHFR gene upregulation by the in-plane mode are similar to those induced by the 45° stress mode. Disrupting stress fibers abolishes differences in cell stiffness, chromatin stretching, and DHFR gene upregulation under different force modes and inhibiting myosin II decreases cell stiffness, chromatin deformation, and gene upregulation. Theoretical modeling using discrete anisotropic stress fibers recapitulates experimental results and reveals underlying mechanisms of force-mode dependence. Our findings suggest that forces impact biological responses of living cells such as gene transcription via previously underappreciated means.


Asunto(s)
Cromatina/química , Fibras de Estrés/química , Tetrahidrofolato Deshidrogenasa/genética , Transcripción Genética/fisiología , Regulación hacia Arriba/fisiología , Animales , Anisotropía , Fenómenos Biomecánicos/genética , Células CHO , Cromatina/metabolismo , Cricetulus , Compuestos Heterocíclicos de 4 o más Anillos/farmacología , Microscopía Intravital , Microscopía Fluorescente , Miosina Tipo II/antagonistas & inhibidores , Miosina Tipo II/metabolismo , Fibras de Estrés/efectos de los fármacos , Fibras de Estrés/metabolismo , Estrés Mecánico , Transcripción Genética/efectos de los fármacos , Regulación hacia Arriba/efectos de los fármacos
11.
Nat Commun ; 11(1): 3802, 2020 07 30.
Artículo en Inglés | MEDLINE | ID: mdl-32732903

RESUMEN

The Sec translocon moves proteins across lipid bilayers in all cells. The Sec channel enables passage of unfolded proteins through the bacterial plasma membrane, driven by the cytosolic ATPase SecA. Whether SecA generates mechanical force to overcome barriers to translocation posed by structured substrate proteins is unknown. Here, we kinetically dissect Sec-dependent translocation by monitoring translocation of a folded substrate protein with tunable stability at high time resolution. We find that substrate unfolding constitutes the rate-limiting step during translocation. Using single-molecule force spectroscopy, we also define the response of the protein to mechanical force. Relating the kinetic and force measurements reveals that SecA generates at least 10 piconewtons of mechanical force to actively unfold translocating proteins, comparable to cellular unfoldases. Combining biochemical and single-molecule measurements thus allows us to define how the SecA motor ensures efficient and robust export of proteins that contain stable structure.


Asunto(s)
Proteínas de Escherichia coli/metabolismo , Escherichia coli/metabolismo , Desplegamiento Proteico , Canales de Translocación SEC/metabolismo , Proteína SecA/metabolismo , Estrés Mecánico , Membrana Celular/metabolismo , Escherichia coli/genética , Proteínas de Escherichia coli/genética , Membrana Dobles de Lípidos/metabolismo , Proteínas de Transporte de Membrana/metabolismo , Metotrexato/metabolismo , NADP/metabolismo , Transporte de Proteínas , Proteína SecA/genética , Tetrahidrofolato Deshidrogenasa/metabolismo
12.
Nat Commun ; 11(1): 4032, 2020 08 12.
Artículo en Inglés | MEDLINE | ID: mdl-32788575

RESUMEN

Hydrogel-based devices are widely used as flexible electronics, biosensors, soft robots, and intelligent human-machine interfaces. In these applications, high stretchability, low hysteresis, and anti-fatigue fracture are essential but can be rarely met in the same hydrogels simultaneously. Here, we demonstrate a hydrogel design using tandem-repeat proteins as the cross-linkers and random coiled polymers as the percolating network. Such a design allows the polyprotein cross-linkers only to experience considerable forces at the fracture zone and unfold to prevent crack propagation. Thus, we are able to decouple the hysteresis-toughness correlation and create hydrogels of high stretchability (~1100%), low hysteresis (< 5%), and high fracture toughness (~900 J m-2). Moreover, the hydrogels show a high fatigue threshold of ~126 J m-2 and can undergo 5000 load-unload cycles up to 500% strain without noticeable mechanical changes. Our study provides a general route to decouple network elasticity and local mechanical response in synthetic hydrogels.


Asunto(s)
Reactivos de Enlaces Cruzados/química , Hidrogeles/química , Poliproteínas/química , Estrés Mecánico , Resinas Acrílicas/química , Fluorescencia , Fenómenos Mecánicos
13.
J Cardiovasc Magn Reson ; 22(1): 59, 2020 08 10.
Artículo en Inglés | MEDLINE | ID: mdl-32772927

RESUMEN

BACKGROUND: Anatomically pre-shaped sinus prostheses (SP) were developed to mimic the aortic sinus with the goal to preserve near physiological hemodynamic conditions after valve-sparing aortic root replacement. Although SP have shown more physiological flow patterns, a comparison to straight tube prosthesis and the analysis of derived quantitative parameters is lacking. Hence, this study sought to analyze differences in aortic wall shear stress (WSS) between anatomically pre-shaped SP, conventional straight tube prostheses (TP), and age-matched healthy subjects) using time-resolved 3-dimensional flow cardiovascular magnetic resonance (4D Flow CMR). Moreover, the WSS gradient was introduced and analyzed regarding its sensitivity to detect changes in hemodynamics and its dependency on the expression of secondary flow patterns. METHODS: Twelve patients with SP (12 male, 62 ± 9yr), eight patients with TP (6 male, 59 ± 9yr), and twelve healthy subjects (2 male, 55 ± 6yr) were examined at 3 T with a 4D Flow CMR sequence in this case control study. Six analysis planes were placed in the thoracic aorta at reproducible landmarks. The following WSS parameters were recorded: WSSavg (spatially averaged over the contour at peak systole), max. WSSseg (maximum segmental WSS), min. WSSseg (minimum segmental WSS) and the WSS Gradient, calculated as max. WSSseg - min. WSSseg. Kruskal-Wallis- and Mann-Whitney-U-Test were used for statistical comparison of groups. Occurrence and expression of secondary flow patterns were evaluated and correlated to WSS values using Spearman's correlation coefficient. RESULTS: In the planes bordering the prosthesis all WSS values were significantly lower in the SP compared to the TP, approaching the physiological optimum of the healthy subjects. The WSS gradient showed significantly different values in the four proximally localized contours when comparing both prostheses with healthy subjects. Strong correlations between an elevated WSS gradient and secondary flow patterns were found in the ascending aorta and the aortic arch. CONCLUSION: Overall, the SP has a positive impact on WSS, most pronounced at the site and adjacent to the prosthesis. The WSS gradient differed most obviously and the correlation of the WSS gradient with the occurrence of secondary flow patterns provides further evidence for linking disturbed flow, which was markedly increased in patients compared to healthy sub jects, to degenerative remodeling of the vascular wall.


Asunto(s)
Aorta Torácica/diagnóstico por imagen , Aorta Torácica/cirugía , Válvula Aórtica/diagnóstico por imagen , Implantación de Prótesis Vascular/instrumentación , Prótesis Vascular , Hemodinámica , Imagen por Resonancia Magnética , Imagen de Perfusión/métodos , Diseño de Prótesis , Adulto , Anciano , Aorta Torácica/fisiopatología , Válvula Aórtica/fisiopatología , Técnicas de Imagen Sincronizada Cardíacas , Estudios de Casos y Controles , Electrocardiografía , Femenino , Humanos , Masculino , Persona de Mediana Edad , Valor Predictivo de las Pruebas , Flujo Sanguíneo Regional , Estrés Mecánico , Resultado del Tratamiento
14.
PLoS One ; 15(8): e0236802, 2020.
Artículo en Inglés | MEDLINE | ID: mdl-32785277

RESUMEN

The static mechanical properties of coal rock show anisotropism, which makes the permeability have anisotropic characteristics partly. The dynamic impact mechanical characteristics of structural anisotropic coal under low and medium strain rates were studied by using self-made vertical Split Hopkinson Bar (SHPB) equipment. The peak stress, the strain rate, dynamic elastic modulus and failure characteristics of raw coal with three coring directions were analyzed under the influence of five impact loads and structural anisotropy. The peak stress increases linearly with impact load, and the maximum strain rate and the dynamic elastic modulus increase exponentially with impact load. The coal samples display anisotropic mechanical characteristics. The values of maximum strain rate, peak stress and dynamic elastic modulus are ranked with directions by the perpendicular to bedding direction (Z direction), the parallel to bedding direction (X direction), and the oblique 45° to bedding direction (Y direction). Dynamic mechanical properties of structural anisotropic coal provide a theoretical basis for gas seepage in far-blasting field.


Asunto(s)
Carbón Mineral/análisis , Módulo de Elasticidad , Gases/química , Estrés Mecánico
15.
Nat Commun ; 11(1): 4321, 2020 08 28.
Artículo en Inglés | MEDLINE | ID: mdl-32859904

RESUMEN

Bacterial colonization of the human intestine requires firm adhesion of bacteria to insoluble substrates under hydrodynamic flow. Here we report the molecular mechanism behind an ultrastable protein complex responsible for resisting shear forces and adhering bacteria to cellulose fibers in the human gut. Using single-molecule force spectroscopy (SMFS), single-molecule FRET (smFRET), and molecular dynamics (MD) simulations, we resolve two binding modes and three unbinding reaction pathways of a mechanically ultrastable R. champanellensis (Rc) Dockerin:Cohesin (Doc:Coh) complex. The complex assembles in two discrete binding modes with significantly different mechanical properties, with one breaking at ~500 pN and the other at ~200 pN at loading rates from 1-100 nN s-1. A neighboring X-module domain allosterically regulates the binding interaction and inhibits one of the low-force pathways at high loading rates, giving rise to a catch bonding mechanism that manifests under force ramp protocols. Multi-state Monte Carlo simulations show strong agreement with experimental results, validating the proposed kinetic scheme. These results explain mechanistically how gut microbes regulate cell adhesion strength at high shear stress through intricate molecular mechanisms including dual-binding modes, mechanical allostery and catch bonds.


Asunto(s)
Adhesión Bacteriana/fisiología , Microbioma Gastrointestinal/fisiología , Fenómenos Mecánicos , Fenómenos Físicos , Bacterias , Adhesión Bacteriana/genética , Proteínas de Ciclo Celular , Proteínas Cromosómicas no Histona , Tracto Gastrointestinal/microbiología , Técnicas de Inactivación de Genes , Humanos , Cinética , Simulación de Dinámica Molecular , Método de Montecarlo , Unión Proteica , Conformación Proteica , Imagen Individual de Molécula , Estrés Mecánico
16.
PLoS One ; 15(8): e0237997, 2020.
Artículo en Inglés | MEDLINE | ID: mdl-32836226

RESUMEN

For the first time, ten frequentist estimation methods are considered on stress-strength reliability R = P(Y < X) when X and Y are two independent Weibull distributions with the same shape parameter. The start point to estimate the parameter R is the maximum likelihood method. Other than the maximum likelihood method, a nine frequentist estimation methods are used to estimate R, namely: least square, weighted least square, percentile, maximum product of spacing, minimum spacing absolute distance, minimum spacing absolute-log distance, method of Cramér-von Mises, Anderson-Darling and Right-tail Anderson-Darling. We also consider two parametric bootstrap confidence intervals of R. We compare the efficiency of the different proposed estimators by conducting an extensive Mont Carlo simulation study. The performance and the finite sample properties of the different estimators are compared in terms of relative biases and relative mean squared errors. The Mont Carlo simulation study revels that the percentile and maximum product of spacing methods are highly competitive with the other methods for small and large sample sizes. To show the applicability and the importance of the proposed estimators, we analyze one real data set.


Asunto(s)
Ingeniería , Distribuciones Estadísticas , Estrés Mecánico , Intervalos de Confianza , Análisis de los Mínimos Cuadrados , Ensayo de Materiales , Método de Montecarlo
17.
PLoS One ; 15(8): e0238112, 2020.
Artículo en Inglés | MEDLINE | ID: mdl-32857805

RESUMEN

This longitudinal study was performed to evaluate the feasibility of detecting the interaction between wall shear stress (WSS) and plaque development. 20 ApoE-/- mice were separated in 12 mice with Western Diet and 8 mice with Chow Diet. Magnetic resonance (MR) scans at 17.6 Tesla and histological analysis were performed after one week, eight and twelve weeks. All in vivo MR measurements were acquired using a flow sensitive phase contrast method for determining vectorial flow. Histological sections were stained with Hematoxylin and Eosin, Elastica van Gieson and CD68 staining. Data analysis was performed using Ensight and a Matlab-based "Flow Tool". The body weight of ApoE-/- mice increased significantly over 12 weeks. WSS values increased in the Western Diet group over the time period; in contrast, in the Chow Diet group the values decreased from the first to the second measurement point. Western Diet mice showed small plaque formations with elastin fragmentations after 8 weeks and big plaque formations after 12 weeks; Chow Diet mice showed a few elastin fragmentations after 8 weeks and small plaque formations after 12 weeks. Favored by high-fat diet, plaque formation results in higher values of WSS. With wall shear stress being a known predictor for atherosclerotic plaque development, ultra highfield MRI can serve as a tool for studying the causes and beginnings of atherosclerosis.


Asunto(s)
Aorta/diagnóstico por imagen , Imagen por Resonancia Magnética , Placa Aterosclerótica/diagnóstico por imagen , Animales , Aorta/patología , Aorta/fisiopatología , Apolipoproteínas E/deficiencia , Apolipoproteínas E/genética , Aterosclerosis/diagnóstico por imagen , Aterosclerosis/patología , Aterosclerosis/fisiopatología , Peso Corporal , Dieta Occidental , Modelos Animales de Enfermedad , Estudios de Factibilidad , Femenino , Estudios Longitudinales , Imagen por Resonancia Magnética/instrumentación , Imagen por Resonancia Magnética/métodos , Ratones Noqueados , Placa Aterosclerótica/patología , Placa Aterosclerótica/fisiopatología , Distribución Aleatoria , Flujo Sanguíneo Regional , Estrés Mecánico
18.
J Oral Sci ; 62(4): 377-381, 2020 Sep 26.
Artículo en Inglés | MEDLINE | ID: mdl-32741850

RESUMEN

In this study, analytic models were used to simulate marginal resection in the area of the second premolar to the second molar region, and the mechanical effects on the mandible of residual bone mass, a maxillofacial prosthesis, and a reconstruction plate were evaluated by three-dimensional finite element analysis. As residual bone mass decreased, maximum principal stress increased near the anterior ramus of the mandible, and maximum shear stress increased at the anterior buccal region of the resected area. In the mandible with a maxillofacial prosthesis, the maximum principal stress distribution at the anterior ramus was lower, and the distribution of maximum shear stress at the anterior buccal region of the resected area was higher. When a reconstruction plate was used, maximum principal stress and maximum shear stress were lower. Thus, lower residual bone mass was associated with increased mandible deflection and torsion. In addition, presence of a maxillofacial prosthesis decreased deflection but increased torsion, and presence of a reconstruction plate decreased deflection and greatly decreased torsion. These findings suggest that decreased residual bone mass and maxillofacial prostheses increase fracture risk; however, presence of a reconstruction plate was effective in decreasing torsional stress, thereby reducing fracture risk in the mandible.


Asunto(s)
Placas Óseas , Prótesis Maxilofacial , Fenómenos Biomecánicos , Análisis de Elementos Finitos , Mandíbula/cirugía , Estrés Mecánico
19.
Eur J Vasc Endovasc Surg ; 60(4): 539-547, 2020 Oct.
Artículo en Inglés | MEDLINE | ID: mdl-32741677

RESUMEN

OBJECTIVE: The rupture of abdominal aortic aneurysms (AAAs) is associated with high mortality despite surgical developments. The determination of aneurysm diameter allows for follow up of aneurysm growth but fails in precisely predicting aneurysm rupture. In this study, time resolved three dimensional ultrasound (4D ultrasound) based wall motion indices (WMIs) are investigated to see if they are capable of distinguishing between uneven affected regions of the aneurysm wall. METHODS: In a prospective study, 56 patients with an AAA were examined using 4D ultrasound. Local longitudinal, circumferential, and shear strains were computed using custom methods. The deformation of the neck and sac of each aneurysm was characterised by statistical indices of the obtained distributions of local wall strains (WMIs): mean and peak strain, heterogeneity index, and local strain ratio. The locations of regions with highest local peak strain were determined. RESULTS: Compared with the aneurysm neck, the sac is characterised by low mean strain, but highly heterogeneous deformation, described by high local strain ratio and heterogeneity index. Differences were highly significant (p < .001) for all strain components. The regions with the highest circumferential peak strain were found more often in the posterior part of the aneurysm neck (p < .050) and sac (p < .001) regions, compared with other wall regions. No statistically significant correlation was found between the WMIs and maximum AAA diameter, except for longitudinal mean strain, which decreased with the increasing diameter (rho = -.42, p < .010). CONCLUSION: Characterisation of wall kinematics by 4D ultrasound based WMIs provides a new and independent criterion for the distinction of diseased tissue in the AAA sac and the less affected neck region. This is a promising step towards the establishment of new biomarkers to differentiate between the mechanical instability of the AAA and rupture risk.


Asunto(s)
Aorta Abdominal/diagnóstico por imagen , Aneurisma de la Aorta Abdominal/diagnóstico por imagen , Interpretación de Imagen Asistida por Computador , Modelos Cardiovasculares , Modelación Específica para el Paciente , Ultrasonografía , Anciano , Anciano de 80 o más Años , Aorta Abdominal/fisiopatología , Aneurisma de la Aorta Abdominal/complicaciones , Aneurisma de la Aorta Abdominal/fisiopatología , Rotura de la Aorta/diagnóstico por imagen , Rotura de la Aorta/etiología , Rotura de la Aorta/fisiopatología , Fenómenos Biomecánicos , Femenino , Hemodinámica , Humanos , Masculino , Persona de Mediana Edad , Valor Predictivo de las Pruebas , Pronóstico , Estudios Prospectivos , Factores de Riesgo , Estrés Mecánico
20.
PLoS One ; 15(8): e0237040, 2020.
Artículo en Inglés | MEDLINE | ID: mdl-32764823

RESUMEN

As type-I-allergies show an increasing prevalence in the general populace, orthodontic patients may also be affected by histamine release during treatment. Human periodontal ligament fibroblasts (PDLF) are regulators of orthodontic tooth movement. However, the impact of histamine on PDLF in this regard is unknown. Therefore PDLF were incubated without or with an orthodontic compressive force of 2g/cm2 with and without additional histamine. To assess the role of histamine-1-receptor (H1R) H1R-antagonist cetirizine was used. Expression of histamine receptors and important mediators of orthodontic tooth movement were investigated. PDLF expressed histamine receptors H1R, H2R and H4R, but not H3R. Histamine increased the expression of H1R, H2R and H4R as well as of interleukin-6, cyclooxygenase-2, and prostaglandin-E2 secretion even without pressure application and induced receptor activator of NF-kB ligand (RANKL) protein expression with unchanged osteoprotegerin secretion. These effects were not observed in presence of H1R antagonist cetirizine. By expressing histamine receptors, PDLF seem to be able to respond to fluctuating histamine levels in the periodontal tissue. Increased histamine concentration was associated with enhanced expression of proinflammatory mediators and RANKL, suggesting an inductive effect of histamine on PDLF-mediated osteoclastogenesis and orthodontic tooth movement. Since cetirizine inhibited these effects, they seem to be mainly mediated via histamine receptor H1R.


Asunto(s)
Histamina/farmacología , Ligamento Periodontal/efectos de los fármacos , Ligamento Periodontal/fisiología , Técnicas de Movimiento Dental , Células Cultivadas , Cetirizina/farmacología , Fibroblastos/citología , Fibroblastos/efectos de los fármacos , Fibroblastos/fisiología , Expresión Génica/efectos de los fármacos , Histamina/fisiología , Antagonistas de los Receptores Histamínicos H1/farmacología , Humanos , Mediadores de Inflamación/metabolismo , Modelos Biológicos , Osteogénesis/efectos de los fármacos , Osteogénesis/fisiología , Osteoprotegerina/genética , Osteoprotegerina/metabolismo , Ligamento Periodontal/citología , Ligando RANK/genética , Ligando RANK/metabolismo , Receptores Histamínicos H1/fisiología , Estrés Mecánico
SELECCIÓN DE REFERENCIAS
DETALLE DE LA BÚSQUEDA