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The state of stress induced by the plane frictionless cylindrical contact. I. The case of elastic similarity
Full text linkThe contact problem between cylindrical conformal surfaces, modelling for instance a fastener joint, is studied. A closed form solution is obtained in Part I of the paper for the case of elastic similarity, improving(i) the solution obtained by Persson (On the Stress Distribution of Cylindrical Elastic Bodies in Contact, Ph.D. dissertation, 1964), which was also limited to identical materials, and(ii) the results of Noble and Hussain (Int. J. Engng. Sci. 7 (1969) 1149), which were limited to the case of perfect fit of contacting materials.The variation of the contact area, pressure distribution and maximum sustainable load is given for the complete range of possible dimensionless loading parameter E1*?R/Q and first Dundurs' material parameter, ?.Under conditions of initial clearance, the contact area arc, var epsilon, increases with load from zero to a limiting value, var epsilonlim, which depends only on the material parameter ?. Vice versa, under conditions of initial interference, the contact is complete until there is detachment and the contact area starts to decrease with load up to the same limiting value, var epsilonlim, which is also the only possible value of contact area for neat-fit conditions, under any applied load.Finally, a complete assessment of the strength of the contact is given for the entire range of working conditions. As expected, the strength of the joint decreases rapidly if the extent of the contact area reduces, and finally tends to the limit predicted by the Hertzian theory when the arc of contact is smaller than about 30°. The optimal conditions for avoiding yielding are reached for a contact arc smaller than the limiting arc var epsilonlim: this means that it is not possible to reach the optimum from a configuration of initial interference
An implantable device for localized drug delivery, uses thereof and a manufacturing method thereof
No full textThe state of stress induced by the plane frictionless cylindrical contact. II. The general case (elastic dissimilarity)
Full text linkIn Part I of the paper, the authors have studied the contact problem between a pin and an infinite plate containing a conforming hole, in the absence of friction and in the case of elastic similarity, obtaining a closed form result which generalizes the identical materials analysis of Persson (On the stress distribution of cylindrical elastic bodies in contact, Ph.D. dissertation, 1964).Here, in Part II, the general case of contacting materials is first studied numerically, finding that the effect of elastic dissimilarity (i.e. the second Dundurs' constant not being zero) is negligible for the dimensionless pressure distribution, the maximum influence being less than 2%. Vice versa, the influence on the relation between the contact area arc semi-width, ?, and the dimensionless loading parameter E1*?R/Q is indeed significant; however, considering as an approximate pressure distribution the one of the elastically similar case, an extremely good approximation is obtained for the general relation ? vs. E1*?R/Q which can now take into account of both Dundurs' elastic parameters. In particular, the limiting value for ? lim, towards which the contact tends under very high loads both under initial clearance or interference (or for any load for the perfect fit limiting case) is given as a function of both Dundurs' elastic parameters, ?, ? as well as the load when complete contact is lost in an interference contact, ? compl.Hence, a complete assessment of the strength of the contact can be obtained directly from the results of Part I of the paper, given that for a certain contact area extension, the correct value of load is used. <br/
The transport of nanoparticles in blood vessels: the effect of vessel permeability and blood rheology
No full textThe longitudinal transport of nanoparticles in blood vessels has been analyzed with blood described as a Casson fluid. Starting from the celebrated Taylor and Aris theory, an explicit expression has been derived for the effective longitudinal diffusion (Deff) depending non-linearly on the rheological parameter xi(c), the ratio between the plug and the vessel radii; and on the permeability parameters pi and omega, related to the hydraulic conductivity and pressure drop across the vessel wall, respectively. An increase of xi(c) or pi has the effect of reducing Deff, and thus both the rheology of blood and the permeability of the vessels may constitute a physiological barrier to the intravascular delivery of nanoparticles
Stress distribution retrieval in granular materials: A multi-scale model and digital image correlation measurements
No full textThe promise of nanotechnology lies in the possibility of engineering matter on the nanoscale and creating technological interfaces that, because of their small scales, may directly interact with biological objects, creating new strategies for the treatment of pathologies that are otherwise beyond the reach of conventional medicine. Nanotechnology is inherently a multiscale, multiphenomena challenge. Fundamental understanding and highly accurate predictive methods are critical to successful manufacturing of nanostructured materials, bio/mechanical devices and systems. In biomedical engineering, and in the mechanical analysis of biological tissues, classical continuum approaches are routinely utilized, even if these disregard the discrete nature of tissues, that are an interpenetrating network of a matrix (the extra cellular matrix, ECM) and a generally large but finite number of cells with a size falling in the micrometer range. Here, we introduce a nano-mechanical theory that accounts for the-non continuum nature of bio systems and other discrete systems. This discrete field theory, doublet mechanics (DM), is a technique to model the mechanical behavior of materials over multiple scales, ranging from some millimeters down to few nanometers. In the paper, we use this theory to predict the response of a granular material to an external applied load. Such a representation is extremely attractive in modeling biological tissues which may be considered as a spatial set of a large number of particulate (cells) dispersed in an extracellular matrix. Possibly more important of this, using digital image correlation (DIC) optical methods, we provide an experimental verification of the model
Time dependent dispersion of nanoparticles in blood vessels
No full textThe dispersion of intravasculary injected nanoparticles can be efficiently described by introducing an effective diffusion coefficient Deff which quantifies the longitudinal mass transport in blood vessels. Here, the original work of Gill and Sankarasubramanian was modified and extended to include 1) the variati- on over time of Deff; 2) the permeability of the blood vessels and 3) non-Newtonian rheology of blood. A general solution was provided for Deff depending on space (x), time (t), plug radius (xc) and a subset of permeability parameters. It was shown that increasing the vessel plug radius (thus hematocrit) or permeability leads to a reduction in Deff, limiting the transport of nanoparticles across those vessels. It was also shown that the asymptotic time beyond which the solution attains the steady state behaviour is always independent of the plug radius and wall permeability. The analysis presented can more accurately predict the transport of nanoparticles in blood vessels, compared to previously developed models
A combined Lattice Boltzmann and Immersed boundary approach for predicting the vascular transport of differently shaped particles
No full textModelling the vascular transport and adhesion of man-made particles is crucial for optimizing their efficacy in the detection and treatment of diseases. Here, a Lattice Boltzmann and Immersed Boundary methods are combined together for predicting the near wall dynamics of particles with different shapes in a laminar flow. For the lattice Boltzmann modelling, a Gauss-Hermite projection is used to derive the lattice equation; wall boundary conditions are imposed through the Zou-He framework; and a moving least squares algorithm accurately reconstructs the forcing term accounting for the immersed boundary. First, the computational code is validated against two well-known test cases: the sedimentation of circular and elliptical cylinders in a quiescent fluid. A very good agreement is observed between the present results and those available in the literature. Then, the transport of circular, elliptical, rectangular, square and triangular particles is analyzed in a Couette flow, at Re=20. All particles drifted laterally across the stream lines reaching an equilibrium position, independently of the initial conditions. For this large Reynolds number, the particle shape has no significant effect on the final equilibrium position but it does affect the absolute value and periodicity of the angular velocity. Specifically, elongated particles show longer oscillation periods and, most interestingly, larger variations in angular velocity. The longest particles exhibit a zero angular velocity for almost the whole rotational period. Collectively, this data demonstrates that the proposed approach can be efficiently used for predicting complex particle dynamics in biologically relevant flows. This computational strategy could have significant impact in the field of computational nanomedicine for optimizing the specific delivery of therapeutic and imaging agents
On the axonal transport of lipid nanoparticles in primary hippocampal neurons
Full text linkAxonal transport is a crucial process in healthy neurons as it supports the intra-cellular movement of nutrients, endogenous substances, and vesicles regulating a broad set of biological functions. Notably, this physiological mechanism is efficiently exploited by a variety of viruses to infect multiple cells within the central nervous system and, thus, it has been proposed as a strategy to enhance the brain penetrance of macromolecules and nanoparticles. In this work, the retrograde and anterograde transport of lipid nanoparticles (LNP) is systematically analyzed in primary hippocampal neurons cultured in compartmentalized microfluidic chips, where neurites are left to grow within 150 μm-long channels connecting the somal and synaptic compartments. After characterizing the physico-chemical properties, toxicological profile, and cell internalization efficiency, the axonal trafficking of fluorescently labeled LNP was monitored over time via live-cell microscopy. Both naïve LNP and apolipoprotein E-coated LNP (ApoE-LNP) were considered under two different experimental configurations, with the LNP being either added to the somal or the synaptic compartment for anterograde or retrograde transport analyses, respectively. ApoE-LNP only were very efficiently uptaken by neurons and rapidly relocated in a perinuclear position. Also, ApoE-LNP incubated in the somal compartment did not translocate along the neurites (null anterograde transport), whereas ApoE-LNP added to the synaptic compartment were detected near the soma already at 30 min post incubation demonstrating retrograde transport velocities up to ∼ 160 nm/s. This preliminary study suggests that ApoE-LNP could be efficiently used to rapidly transport a variety of therapeutic and imaging cargos from the synaptic cleft to the somal compartment
The margination propensity of spherical particles for vascular targeting in the microcirculation
No full textThe propensity of circulating particles to drift laterally towards the vessel walls (margination) in the microcirculation has been experimentally studied using a parallel plate flow chamber. Fluorescent polystyrene particles, with a relative density to water of just 50 g/cm3comparable with that of liposomal or polymeric nanoparticles used in drug delivery and bio-imaging, have been used with a diameter spanning over three order of magnitudes from 50 nm up to 10 mum. The number n approximately s MathType@MTEF@5@5@+=feaagaart1ev2aaatCvAUfKttLearuWrP9MDH5MBPbIqV92AaeXatLxBI9gBaebbnrfifHhDYfgasaacPC6xNi=xH8viVGI8Gi=hEeeu0xXdbba9frFj0xb9qqpG0dXdb9aspeI8k8fiI+fsY=rqGqVepae9pg0db9vqaiVgFr0xfr=xfr=xc9adbaqaaeGaciGaaiaabeqaaeqabiWaaaGcbaGafmOvayLbaGaadaWgaaWcbaGaem4Camhabeaaaaa@2EB4@ of particles marginating per unit surface have been measured through confocal fluorescent microscopy for a horizontal chamber, and the corresponding total volume V approximately s MathType@MTEF@5@5@+=feaagaart1ev2aaatCvAUfKttLearuWrP9MDH5MBPbIqV92AaeXatLxBI9gBaebbnrfifHhDYfgasaacPC6xNi=xH8viVGI8Gi=hEeeu0xXdbba9frFj0xb9qqpG0dXdb9aspeI8k8fiI+fsY=rqGqVepae9pg0db9vqaiVgFr0xfr=xfr=xc9adbaqaaeGaciGaaiaabeqaaeqabiWaaaGcbaGafmOvayLbaGaadaWgaaWcbaGaem4Camhabeaaaaa@2EB4@ of particles has been calculated. Scaling laws have been derived as a function of the particle diameter d. In horizontal capillaries, margination is mainly due to the gravitational force for particles with d > 200 nm and V approximately s MathType@MTEF@5@5@+=feaagaart1ev2aaatCvAUfKttLearuWrP9MDH5MBPbIqV92AaeXatLxBI9gBaebbnrfifHhDYfgasaacPC6xNi=xH8viVGI8Gi=hEeeu0xXdbba9frFj0xb9qqpG0dXdb9aspeI8k8fiI+fsY=rqGqVepae9pg0db9vqaiVgFr0xfr=xfr=xc9adbaqaaeGaciGaaiaabeqaaeqabiWaaaGcbaGafmOvayLbaGaadaWgaaWcbaGaem4Camhabeaaaaa@2EB4@ increases with d4; whereas for smaller particles V approximately s MathType@MTEF@5@5@+=feaagaart1ev2aaatCvAUfKttLearuWrP9MDH5MBPbIqV92AaeXatLxBI9gBaebbnrfifHhDYfgasaacPC6xNi=xH8viVGI8Gi=hEeeu0xXdbba9frFj0xb9qqpG0dXdb9aspeI8k8fiI+fsY=rqGqVepae9pg0db9vqaiVgFr0xfr=xfr=xc9adbaqaaeGaciGaaiaabeqaaeqabiWaaaGcbaGafmOvayLbaGaadaWgaaWcbaGaem4Camhabeaaaaa@2EB4@ increases with d3. In vertical capillaries, since the particles are heavier than the fluid they would tend to marginate towards the walls in downward flows and towards the center in upward flows, with V approximately s MathType@MTEF@5@5@+=feaagaart1ev2aaatCvAUfKttLearuWrP9MDH5MBPbIqV92AaeXatLxBI9gBaebbnrfifHhDYfgasaacPC6xNi=xH8viVGI8Gi=hEeeu0xXdbba9frFj0xb9qqpG0dXdb9aspeI8k8fiI+fsY=rqGqVepae9pg0db9vqaiVgFr0xfr=xfr=xc9adbaqaaeGaciGaaiaabeqaaeqabiWaaaGcbaGafmOvayLbaGaadaWgaaWcbaGaem4Camhabeaaaaa@2EB4@ increasing with d9/2. However, the margination in vertical capillaries is predicted to be much smaller than in horizontal capillaries. These results suggest that, for particles circulating in an external field of volume forces (gravitation or magnetic), the strategy of using larger particles designed to marginate and adhere firmly to the vascular walls under flow could be more effective than that of using particles sufficiently small (d < 200 nm) to hopefully cross a discontinuous endothelium
A doublet mechanics model for the ultrasound characterization of malignant tissues
No full textNon invasive ultrasound-based imaging systems are being more commonly used in clinical bio-microscopy applications for both ex vivo and in vivo analysis of tissue pathological and physiological states. These modalities usually employ high-frequency ultrasound systems to overcome spatial resolution limits of conventional clinical diagnostic approaches. Biological tissues are non continuous, non homogeneous and exhibit a multiscale organization from the sub-cellular level (<1 mm) to the organ level (<1 cm). When the ultrasonic wavelength used to probe the tissues becomes comparable with the tissue’s microstructure scale, the propagation and reflection of ultrasound waves cannot be fully interpreted employing classical models developed within the continuum assumption. In this study, we present a multiscale model for analyzing the mechanical response of a non-continuum double-layer system exposed to an ultrasound source. The model is developed within the framework of the Doublet Mechanics theory and can be applied to the non-invasive analysis of complex biological tissues
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