scholarly journals Actuators for MRE: New Perspectives With Flexible Electroactive Materials

2021 ◽  
Vol 9 ◽  
Author(s):  
Jean-Lynce Gnanago ◽  
Jean-Fabien Capsal ◽  
Tony Gerges ◽  
Philippe Lombard ◽  
Vincent Semet ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Magnetic Resonance ◽  
Electromagnetic Compatibility ◽  
Tissue Characterization ◽  
Physiological State ◽  
Shear Stiffness ◽  
Biological Tissues ◽  
Ease Of Use ◽  
Mechanical Coupling ◽  
Electroactive Materials

Since 1995, Magnetic Resonance Elastography (MRE) has been constantly developed as a non-invasive diagnostic tool for quantitative mapping of mechanical properties of biological tissues. Indeed, mechanical properties of tissues vary over five orders of magnitude (the shear stiffness is ranging from 102 Pa for fat to 107 Pa for bones). Additionally, these properties depend on the physiological state which explains the granted benefit of MRE for staging liver fibrosis and its potential in numerous medical and biological domains. In comparison to the other modalities used to perform such measurement, Magnetic Resonance (MR) techniques offer the advantages of acquiring 3D high spatial resolution images at high penetration depth. However, performing MRE tissue characterization requires low frequency shear waves propagating in the tissue. Inducing them is the role of a mechanical actuator specifically designed to operate under Magnetic Resonance Imaging (MRI) specific restrictions in terms of electromagnetic compatibility. Facing these restrictions, many different solutions have been proposed while keeping a common structure: a vibration generator, a coupling device transmitting the vibration and a piston responsible for the mechanical coupling of the actuator with the tissue. The following review details the MRI constraints and how they are shaping the existing actuators. An emphasis is put on piezoelectric solutions as they solve the main issues encountered with other actuator technologies. Finally, flexible electroactive materials are reviewed as they could open great perspectives to build new type of mechanical actuators with better adaptability, greater ease-of-use and more compactness of dedicated actuators for MRE of small soft samples and superficial organs such as skin, muscles or breast.

scholarly journals Magnetic resonance assessment of parenchymal elasticity in normal and edematous, ventilator-injured lung

2012 ◽  
Vol 113 (4) ◽  
pp. 666-676 ◽  
Author(s):  
Kiaran P. McGee ◽  
Yogesh K. Mariappan ◽  
Rolf D. Hubmayr ◽  
Rickey E. Carter ◽  
Zhonghao Bao ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Magnetic Resonance ◽  
Ex Vivo ◽  
Spin Echo ◽  
Shear Stiffness ◽  
Normal Lung ◽  
Imaging Method ◽  
Filling Material ◽  
Sprague Dawley ◽  
Normal Lungs

Magnetic resonance elastography (MRE) is a MR imaging method capable of spatially resolving the intrinsic mechanical properties of normal lung parenchyma. We tested the hypothesis that the mechanical properties of edematous lung exhibit local properties similar to those of a fluid-filled lung at transpulmonary pressures (Ptp) up to 25 cm H2O. Pulmonary edema was induced in anesthetized female adult Sprague-Dawley rats by mechanical ventilation to a pressure of 40 cm H2O for ∼30 min. Prior to imaging the wet weight of each ex vivo lung set was measured. MRE, high-resolution T1-weighted spin echo and T2* gradient echo data were acquired at each Ptp for both normal and injured ex vivo lungs. At Ptps of 6 cm H2O and greater, the shear stiffness of normal lungs was greater than injured lungs ( P ≤ 0.0003). For Ptps up to 12 cm H2O, shear stiffness was equal to 1.00, 1.07, 1.16, and 1.26 kPa for the injured and 1.31, 1.89, 2.41, and 2.93 kPa for normal lungs at 3, 6, 9, and 12 cm H2O, respectively. For injured lungs MRE magnitude signal and shear stiffness within regions of differing degrees of alveolar flooding were calculated as a function of Ptp. Differences in shear stiffness were statistically significant between groups ( P < 0.001) with regions of lower magnitude signal being stiffer than those of higher signal. These data demonstrate that when the alveolar space filling material is fluid, MRE-derived parenchymal shear stiffness of the lung decreases, and the lung becomes inherently softer compared with normal lung.

Tire Treadwear — A Comprehensive Evaluation of the Factors: Generic Type, Aspect Ratio, Tread Pattern, and Tread Composition Part IV: Laboratory Measurement of Mechanical Properties and Mechanical Actions of Tires Relating to Treadwear

1986 ◽  
Vol 14 (4) ◽  
pp. 264-291
Author(s):  
K. L. Oblizajek ◽  
A. G. Veith
Keyword(s):  
Mechanical Properties ◽  
Shear Stress ◽  
Contact Zone ◽  
Flexural Rigidity ◽  
Comprehensive Evaluation ◽  
Shear Stiffness ◽  
Shear Stresses ◽  
Lateral Shear ◽  
Band Bending ◽  
Tread Rubber

Abstract Treadwear is explained by specific mechanical properties and actions of tires. Rubber shear stresses in the contact zone between the tire and the road become large at large slip angles. When normal stresses are insufficient to prevent sliding at the rear of the footprint, wear occurs at a rate that depends on test severity. Two experimental approaches are described to relate treadwear to tire characteristics. The first uses transducers imbedded in a simulated road surface to obtain direct measurements of contact stresses on the loaded, freely-rolling, steered tires. The second approach is developed with the aid of a simple carcass, tread-band, tread-rubber tire model. Various tire structural configurations; characterized by carcass spring rate, edgewise flexural band stiffness, and tread rubber shear stiffness; are simulated and lateral shear stress response in the contact zone is determined. Tires featuring high band stiffness and low carcass stiffness generate lower lateral shear stress levels. Furthermore, coupling of tread-rubber stiffness and band flexural rigidity are important in determining level of shear stresses. Laboratory measurements with the described apparatus produced values of tread-band bending and carcass lateral stiffness for several tire constructions. Good correlation is shown between treadwear and a broad range of tire stiffness and test course severities.

scholarly journals Beam Theory of Thermal–Electro-Mechanical Coupling for Single-Wall Carbon Nanotubes

Nanomaterials ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 923
Author(s):  
Kun Huang ◽  
Ji Yao
Keyword(s):  
Mechanical Properties ◽  
Carbon Nanotubes ◽  
Beam Theory ◽  
Bending Stiffness ◽  
Single Wall Carbon Nanotubes ◽  
Beam Model ◽  
Euler Beam ◽  
New Model ◽  
Mechanical Coupling ◽  
Electrostatic Fields

The potential application field of single-walled carbon nanotubes (SWCNTs) is immense, due to their remarkable mechanical and electrical properties. However, their mechanical properties under combined physical fields have not attracted researchers’ attention. For the first time, the present paper proposes beam theory to model SWCNTs’ mechanical properties under combined temperature and electrostatic fields. Unlike the classical Bernoulli–Euler beam model, this new model has independent extensional stiffness and bending stiffness. Static bending, buckling, and nonlinear vibrations are investigated through the classical beam model and the new model. The results show that the classical beam model significantly underestimates the influence of temperature and electrostatic fields on the mechanical properties of SWCNTs because the model overestimates the bending stiffness. The results also suggest that it may be necessary to re-examine the accuracy of the classical beam model of SWCNTs.

scholarly journals Nonlinear modelling of the seismic response of masonry structures: Calibration strategies

2021 ◽  
Author(s):  
Antonio Maria D’Altri ◽  
Francesco Cannizzaro ◽  
Massimo Petracca ◽  
Diego Alejandro Talledo
Keyword(s):  
Mechanical Properties ◽  
Numerical Models ◽  
Shear Stiffness ◽  
Model Material ◽  
National Standards ◽  
National Standard ◽  
Masonry Structures ◽  
Nonlinear Modelling ◽  
Various Boundary Conditions ◽  
Panel Stiffness

AbstractIn this paper, a simple and practitioners-friendly calibration strategy to consistently link target panel-scale mechanical properties (that can be found in national standards) to model material-scale mechanical properties is presented. Simple masonry panel geometries, with various boundary conditions, are utilized to test numerical models and calibrate their mechanical properties. The calibration is successfully conducted through five different numerical models (most of them available in commercial software packages) suitable for nonlinear modelling of masonry structures, using nonlinear static analyses. Firstly, the panel stiffness calibration is performed, focusing the attention to the shear stiffness. Secondly, the panel strength calibration is conducted for several axial load ratios by attempts using as reference the target panel strength deduced by well-known analytical strength criteria. The results in terms of panel strength for the five different models show that this calibration strategy appears effective in obtaining model properties coherent with Italian National Standard and Eurocode. Open issues remain for the calibration of the post-peak response of masonry panels, which still appears highly conventional in the standards.

scholarly journals Diagnostic Role of Cardiovascular Magnetic Resonance Imaging in Dilated Cardiomyopathy

2021 ◽  
Author(s):  
Nehal Singla ◽  
Shibani Mehra ◽  
Umesh C. Garga
Keyword(s):  
Cardiac Magnetic Resonance ◽  
Magnetic Resonance ◽  
Dilated Cardiomyopathy ◽  
Tissue Characterization ◽  
Ventricular Dysfunction ◽  
Intravenous Contrast ◽  
Morphologic Characteristics ◽  
Myocardial Tissue Characterization ◽  
Diagnostic Role ◽  
Appropriate Therapy

Abstract Aims The purpose of the study was to compare the accuracy of cardiac magnetic resonance (CMR) with echocardiography for the evaluation of ventricular dysfunction in patients of dilated cardiomyopathy (DCM). Further, we evaluated the potential of CMR for myocardial tissue characterization. Design Prospective observational. Materials and Methods A total of 30 patients with suspected DCM prospectively underwent cardiac magnetic resonance (MR) using a 1.5 Tesla MR scanner, with appropriate phased-array body coils. Dynamic sequences after injection of 0.1 mmol/kg of body weight of gadolinium-based intravenous contrast (Magnevist) were acquired for each patient, after which delayed images were obtained at an interval of 12 to 15 minutes. Myocardial tagging was performed in all patients for assessment of wall motion abnormalities. Each MR examination was interpreted with two radiologists for chamber dimensions and ventricular dysfunction as well as morphologic characteristics with disagreement resolved by consensus. All patients included in the study were taken up for MR evaluation after cardiological evaluation through echocardiography and the results for both the studies were compared. Data were analyzed through standard statistical methods. Conclusion CMR is a comprehensive diagnostic tool, which can estimate the ventricular function more precisely than echocardiography. CMR reliably differentiates between ischemic and nonischemic etiologies of DCM based on patterns of late gadolinium enhancement (LGE) and based on the presence or absence of LGE, which helps to estimate the degree of myocardial fibrosis. Thereby it can be a useful tool in establishing risk stratification, predicting prognosis, and thus instituting appropriate therapy in DCM patients.

scholarly journals Lorentz force induced shear waves for magnetic resonance elastography applications

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Guillaume Flé ◽  
Guillaume Gilbert ◽  
Pol Grasland-Mongrain ◽  
Guy Cloutier
Keyword(s):  
Magnetic Resonance ◽  
Shear Wave ◽  
Lorentz Force ◽  
Wave Attenuation ◽  
Shear Waves ◽  
Estimation Method ◽  
Biological Tissues ◽  
Magnetic Resonance Elastography ◽  
Motion Generation ◽  
Wave Source

AbstractQuantitative mechanical properties of biological tissues can be mapped using the shear wave elastography technique. This technology has demonstrated a great potential in various organs but shows a limit due to wave attenuation in biological tissues. An option to overcome the inherent loss in shear wave magnitude along the propagation pathway may be to stimulate tissues closer to regions of interest using alternative motion generation techniques. The present study investigated the feasibility of generating shear waves by applying a Lorentz force directly to tissue mimicking samples for magnetic resonance elastography applications. This was done by combining an electrical current with the strong magnetic field of a clinical MRI scanner. The Local Frequency Estimation method was used to assess the real value of the shear modulus of tested phantoms from Lorentz force induced motion. Finite elements modeling of reported experiments showed a consistent behavior but featured wavelengths larger than measured ones. Results suggest the feasibility of a magnetic resonance elastography technique based on the Lorentz force to produce an shear wave source.

scholarly journals Protein Hydrogels: The Swiss Army Knife for Enhanced Mechanical and Bioactive Properties of Biomaterials

Nanomaterials ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 1656
Author(s):  
Carla Huerta-López ◽  
Jorge Alegre-Cebollada
Keyword(s):  
Mechanical Properties ◽  
Tissue Engineering ◽  
Polymer Networks ◽  
Biological Tissues ◽  
Modern Medicine ◽  
Body Parts ◽  
Biomedical Sciences ◽  
Protein Hydrogels ◽  
Large Water ◽  
Design Options

Biomaterials are dynamic tools with many applications: from the primitive use of bone and wood in the replacement of lost limbs and body parts, to the refined involvement of smart and responsive biomaterials in modern medicine and biomedical sciences. Hydrogels constitute a subtype of biomaterials built from water-swollen polymer networks. Their large water content and soft mechanical properties are highly similar to most biological tissues, making them ideal for tissue engineering and biomedical applications. The mechanical properties of hydrogels and their modulation have attracted a lot of attention from the field of mechanobiology. Protein-based hydrogels are becoming increasingly attractive due to their endless design options and array of functionalities, as well as their responsiveness to stimuli. Furthermore, just like the extracellular matrix, they are inherently viscoelastic in part due to mechanical unfolding/refolding transitions of folded protein domains. This review summarizes different natural and engineered protein hydrogels focusing on different strategies followed to modulate their mechanical properties. Applications of mechanically tunable protein-based hydrogels in drug delivery, tissue engineering and mechanobiology are discussed.

scholarly journals Concomitant control of mechanical properties and degradation in resorbable elastomer-like materials using stereochemistry and stoichiometry for soft tissue engineering

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Mary Beth Wandel ◽  
Craig A. Bell ◽  
Jiayi Yu ◽  
Maria C. Arno ◽  
Nathan Z. Dreger ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Drug Delivery ◽  
Soft Tissue ◽  
Tissue Regeneration ◽  
Biological Tissues ◽  
Soft Tissue Regeneration ◽  
Soft Tissue Engineering ◽  
Degradation Properties ◽  
Enhance Cell Adhesion

AbstractComplex biological tissues are highly viscoelastic and dynamic. Efforts to repair or replace cartilage, tendon, muscle, and vasculature using materials that facilitate repair and regeneration have been ongoing for decades. However, materials that possess the mechanical, chemical, and resorption characteristics necessary to recapitulate these tissues have been difficult to mimic using synthetic resorbable biomaterials. Herein, we report a series of resorbable elastomer-like materials that are compositionally identical and possess varying ratios of cis:trans double bonds in the backbone. These features afford concomitant control over the mechanical and surface eroding degradation properties of these materials. We show the materials can be functionalized post-polymerization with bioactive species and enhance cell adhesion. Furthermore, an in vivo rat model demonstrates that degradation and resorption are dependent on succinate stoichiometry in the elastomers and the results show limited inflammation highlighting their potential for use in soft tissue regeneration and drug delivery.

scholarly journals Cardiac magnetic resonance imaging in differential diagnosis of cardiac masses

2021 ◽  
Vol 22 (Supplement_1) ◽  
Author(s):  
EC D"angelo ◽  
P Paolisso ◽  
L Bergamaschi ◽  
A Foa ◽  
I Magnani ◽  
...  
Keyword(s):  
Differential Diagnosis ◽  
Cardiac Magnetic Resonance ◽  
Magnetic Resonance ◽  
Pericardial Effusion ◽  
Tissue Characterization ◽  
Descriptive Analysis ◽  
Gadolinium Enhancement ◽  
Malignant Lesions ◽  
T1 And T2 ◽  
Cardiac Masses

Abstract Funding Acknowledgements Type of funding sources: Public hospital(s). Main funding source(s): S. Orsola Hospital Background  Differential diagnosis of cardiac masses represents a challenging issue with important implications for therapeutic management and patient’s prognosis. Cardiac Magnetic Resonance (CMR) is a non-invasive imaging technique used to characterize morphologic and functional features of masses. Integration of these information can lead an accurate diagnosis. Purpose  To evaluate the diagnostic role of CMR in defining the nature of cardiac masses. Methods : Ninety-three patients with cardiac masses evaluated with CMR were enrolled. All masses had histological certainty. CMR sequences allowed a qualitative morphologic description as well as tissue characterization. Evaluation of masses morphology included localization, size and borders assessment, detection of potential multiple lesions and pericardial effusion. Tissue characterization resulted from an estimation of contrast enhancement - early gadolinium enhancement (EGE) and late gadolinium enhancement (LGE) sequences - and tissue homogeneity in T1 and T2 weighted acquisitions. The descriptive analysis was carried out by comparing benign vs malignant lesions as well as dividing patients into 4 subgroups: primitive benign tumours, primitive malignant tumours, metastatic tumours and pseudotumours.  Results  The descriptive analysis of the morphologic features showed that diameter &gt; 50mm, invasion of surrounding planes, irregular margins and presence of pericardial effusion were able to predict malignancy (p &lt; 0.001). As for tissue characteristics, heterogeneous signal intensity - independently from T1 and T2 weighted acquisitions - and EGE were more common in malignant lesions (p &lt;0.001). When analysing the four subgroups, CMR features did not discriminate between primitive malignant masses and metastasis. Conversely, hyperintensity signal and EGE were able to distinguish benign primitive lesions from pseudotumors (p = 0.002).  Furthermore, using classification and regression tree (CART) analysis, we developed an algorithm to differentiate masses: invasion of surrounding planes was a common characteristic of malignancy and identifies itself malignant tumors. In the absence of invasive features, gadolinium enhancement was evaluated: the lack of contrast uptake was able to exclude a pseudotumor diagnosis and reduced the probability of a primary benign tumor.  Conclusions Cardiac magnetic resonance is a very powerful diagnostic tool for differential diagnosis of cardiac masses as it correctly addresses malignancy. Furthermore, an accurate evaluation of the several CMR features, may discriminate primary benign masses and pseudotumours. Abstract Figure. Benign and malignant cardiac masses

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