1,721,144 research outputs found
Cornea modelling
Full text linkBackground Biomechanics introduces numerous technologies to support clinical practice in ophthalmology, with the goal of improving surgical outcomes and to develop new advanced technologies with minimum impact on clinical training. Unfortunately, a few misconceptions on the way that computational methods should be applied to living tissues contributes to a lack of confidence towards computer-based approaches. Methods Corneal biomechanics relies on sound theories of mechanics, including concepts of equilibrium, geometrical measurements, and complex material behaviors. The peculiarities of biological tissues require the consideration of multi-physics, typical of the eye environment, and to adopt customized geometrical models constructed on the basis of advanced optical imaging and in-vivo testing. Results Patient-specific models are able to predict the outcomes of refractive surgery and to exploit the results of in-vivo test to characterize the material properties of the corneal tissue. Conclusions Corneal biomechanics can become an important support to clinical practice, provided that methods are based on the actual multi-physics and use customized geometrical and mechanical models
Dietary Bioactives: Their Role in the Prevention and Treatment of Cardiovascular and Metabolic Bone Diseases
Full text linkCardiovascular and metabolic bone diseases are demanding health problems with high morbidity and mortality [...]
Analysis on the Dynamic Wave Attenuation Properties of Metaconcrete Considering a Quasi-Random Arrangement of Inclusions
Full text linkThe mitigation properties of metaconcrete cast with two types of resonant inclusions are assessed through wave transmission tests. Three cylindric metaconcrete specimens of regular size (20 cm height, 10 cm diameter), containing an equal number of different type of inclusions disposed in a semi-regular lattice, are tested in the longitudinal direction within the sonic range of frequencies. Inclusions, bi-material spheres consisting of a heavy core coated with a soft material, are characterized by a resonant behavior, evaluated numerically with a finite element modal analysis of a unit metaconcrete cell. Each metaconcrete specimen contains six layers consisting of six engineered aggregates of different type. Inclusions are disposed by rotating each layer with respect to the adjacent ones, as so as to create a pseudo-random arrangement. Specimens are excited by a sinusoidal signal of linearly growing frequency, sweeping a range centered at the translational eigenfrequency of the resonant inclusion. A standard plain concrete specimen is used as reference to define a transmissibility coefficient, that facilitates the quantification of the attenuation properties. With respect to plain concrete, all metaconcrete specimens show a marked (up to 80–90%) attenuation of the transmitted signal in proximity of the numerically estimated eigenfrequency of the inclusion. The intensity of the attenuation is weakly dependent on the type of the inclusion, while the frequency where the attenuation is observed depends markedly on the inclusion type. As a very positive quality in the view of practical applications, experimental results confirm that the attenuation effectiveness of metaconcrete is not related to the ordered microstructural arrangement
Use of effective multiscale cohesive models in the simulation of spall in metal plates
No full textDuctile fracture of metals is the net result of void nucleation, growth and coalescence mechanisms that operate at the microscale. Optimal scaling analysis provides the analytical form of the effective material law that models the ductile fracture phenomena at the macroscale. The upscaled model of ductile behavior assumes the form of a cohesive relation-surface traction versus displacement-of the power-law type with well-defined exponents. In the present work, we demonstrate how the effective cohesive law derived from optimal scaling can be conveniently inserted into macroscale calculations by recourse to cohesive elements. The plastic deformation outside the cohesive elements is of moderate size and can be modeled by means of conventional plasticity models. In particular, the mesh size is dictated by accuracy considerations at the macroscale structural level and is not in any way constrained by microscale features and mechanisms, which happen at the subgrid level and are accounted for by the effective cohesive law. We illustrate the multiscale paradigm by means of spall calculations
Fiber distributed hyperelastic modeling of biological tissues
No full textIn view of a more realistic description of the spatial distribution of the collagen fibers in soft biological tissues, for example the human cornea, we propose a material model alternative to the one based on generalized structure tensors, proposed by Gasser et al. (2006). We assume that the strain energy function depends on the mean value and on the variance of the pseudo-invariant (I) over bar (4) of the distribution of the fibers. Indeed, the mean value was the only term considered in the original generalized structure tensor model. We derive the expression of the stress and of the consistent tangent stiffness of the new model and compare its mechanical response with the one of the original model for standard uniaxial, shear and biaxial tests. The comparisons are made with reference to the response of the exact fiber dispersed model, based on the direct integration of the contribution of the fibers
A predictive model of UV-A-riboflavin crosslinking treatment on porcine corneas
Full text linkThe crosslinking technique (CXL) is an effective low-risk
therapeutic treatment of keratoconus and other
ectatic disorders of the human cornea. The effect
of corneal CXL is to increase the stiffness of the
stroma to prevent the progression of the cornea
distortion. Several clinical and experimental studies
have shown that the stiffening effects predominantly
localise on the anterior portion of the stroma and
that the in-depth stiffening distribution is highly
dependent on the duration of treatment. Yet, how
the stiffening effects distribute through the cornea
thickness as a function of the treatment duration is
an open question. Here we propose an analytical
model of the stiffening profile due to CXL-treatment
as a function of the irradiation time. We consider
linear and nonlinear variations of the crosslinking
effects across the thickness and implement them into
a finite element model of the porcine cornea. We
present a time-dependent in-depth stiffening profile
that allows us to predict the post-operative corneas
response to physiological intraocular pressure for
different irradiation times. We anticipate that this
predictive model will support the development of
patient specific 3D models that will allow clinicians
to design customised CXL treatment, thus enhancing
treatment outcomes
A multi-field model for charging and discharging of lithium-ion battery electrodes
Full text linkAn electrochemical–thermomechanical model for the description of charging and discharging processes in lithium electrodes is presented. Multi-physics coupling is achieved through the constitutive relations, obtained within a consistent thermodynamic framework based on the definition of the free energy density, sum of distinct contributions from different physics. The system is characterized by finite kinematics, under the assumption of locality of deformation, and the deformation gradient is decomposed into the product of elastic and inelastic parts. Specifically, a Taylor series expansion is used to approximate the inelastic deformation due to ion intercalation. The elastic part can be described alternatively by two finite kinematics models of neo-Hookean elasticity, and a Maxwell-type viscoelastic model accounts for time-dependent mechanical aspects. The model is implemented into a finite element code that uses B-spline basis functions. We illustrate the features of the model by means of selects examples, showing that chemo-mechanical interaction affects the equilibrium concentrations of the phases. The model captures the fundamental aspects of the anode charging and discharging processes. © 2020, The Author(s)
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