1,721,028 research outputs found
Biomechanical Growth Laws for Arterial Walls
No full textWe present some results concerning the remodeling of arterial vessels
having a capacity for adaptation in response to biomechanical stimuli. In
particular, we focus the attention on the mechanical feedback from the biochemical
control system described by outer accretive forces, and on the role
of these forces in driving the remodeling phenomena that compensate modifications
of blood flow or ageing processes
Models for striated muscles
No full textWe describe some known aspects of the mechanics of activated muscles
using a model for materials susceptible of remodeling. We present some
results on the mechanics and the energetics associated to different muscular
exercises as isotonic and isometric contractions. Moreover, we discuss
the modeling of some typical memory dependent phenomena such as force
enhancement/depression following stretching/shortening
Adaptive Remodelling of Arterial Walls
No full textWe present some results concerning the modelling of growth phenomena in an artery section.
In particular, we focus the attention on the role of the outer accretive forces, describing the
mechanical feedback from the biochemical control system, in the remodelling process. We view
such forces as the control parameters of the evolution of the relaxed state of the body and
prescribe them constitutively in such a way that the evolution process tend to a well-dened
limit (the so-called homeostatic conguration of the body
Cavitation-enhanced permeability in a vessel on a chip
Full text linkMethods combining ultrasound and microbubbles (USMB) offer the unique capability of non-invasively, locally and transiently increase endothelial permeability [1]. This is crucial for the delivery of pharmaceutical agents, injected into the blood circulation, since the real efficiency of a therapy depends on the rate and ability of a macromolecules to cross the endothelial barrier and reach the intended target. Molecule passage through this biological barrier is hampered by the endothelium, lining the innermost surface of blood vessels, consisting of a continuum layer of specialized cells close together to form a size-selective membrane. In this contest, cavitation-assisted permeation shows promise for reversibly altering the barrier integrity, opening gaps between endothelial cells and doing so facilitating the diffusion of pharmaceutical agents out of vessel.
Although acoustic cavitation is already exploited in in vivo animal models for drug delivery testing, the in vitro approach offers the possibility to obtain well-controlled procedures, saving in cost and time [2]. Here, a platform integrating in vitro blood vessels and acoustic cavitation is used to test the feasibility of micro bubbles (MBs) cavitation-enhanced endothelial permeability.
We induce MBs (Sonovue® contrast agent) stable cavitation, evoked by low-intensity ultrasound exposure (Mechanical Index (MI) = 0.4, 0.72), in a microfluidic device purposely designed [3] to mimic micro-blood vessel. The bio-inspired device consists in a PDMS microfluidic network with a central circular tissue compartment enclosed by two independent vascular channels mimicking the three-dimensional morphology, size and flow characteristics of a micro vessel in vivo. The device is previously cultured with Human Umbilical Vein Endothelial Cells (HUVECs) with a reliable and reproducible protocol [4] that allows endothelial cells to form a complete lumen under physiological shear stresses. Immunofluorescence microscopy is then exploited in order to monitor vascular integrity following vascular endothelial cadherin (VE-Cadherin), the most determinant protein for vascular permeability.
The endothelial membrane permeability is evaluated through a dedicated optical/acoustic set-up in presence of ultrasound-activated MBs driven by 1 MHz-unfocused transducer. The basic set up is designed and adapted to host the bio-inspired device, the piezoelectric transducers within a water-filled and temperature-controlled costume chamber located on the microscope stage.
Measurements of fluorescent dye diffusion towards the biological membrane has been carried out with a time lapse acquisition under a confocal microscope operated in epifluorescence mode. An
image analysis on the intensity change due to fluorescence accumulation in the tissue compartment is performed to obtain quantification of permeability.
Intercellular gaps were firstly identified by inspection using ImageJ software and then post-processed in order to increase the contrast and binarize the image using a threshold method with the same cut-off value for all Regions of Interest. The gap area was then quantified counting the black pixels of the central connected blob in each binarized image. The results show that MBs amplify the ultrasound effect, leading to the formation of inter-endothelial gaps, proportionally to the applied acoustic pressure, and causing barrier permeabilization. Moreover, endothelium recovery was completely achieved after 45 minutes from the USMB exposure with gap area distribution returning to the control levels.
To conclude, the proposed integrated platform allows for precise and repeatable in vitro measurements of cavitation-enhanced endothelium permeability providing a novel methodology for the quantitative understanding of cavitation assisted drug delivery.
[1] K. Kooiman, H. J. Vos, M. Versluis, and N. de Jong, “Acoustic behaviour of microbubbles and implications for drug delivery,” Advanced drug delivery reviews, vol. 72, pp. 28–48, 2014.
[2] Peruzzi, G. Perspective on cavitation enhanced endothelial layer permeabiliry, Colloids and surface B: biointerfaces 168 (2018), 3-93
[3] S.P.Deosarkar, et al. A novel dynamic neonatal blood-brain barrier on a chip, Plos One, 10(11) (2015), p. e014272
IDENTIFICAZIONE DEI PARAMETRI COSTITUTIVI DI TRAVI AFFINI
No full textSi presenta una procedura di identificazione che permette di derivare la prescrizione costitutiva
di un modello affine di trave nota quella del modello tridimensionale alla Cauchy.
A differenza di quanto si fa usualmente, la procedura si basa sulla richiesta che l’energia
complementare elastica dei due modelli sia la stessa quando valutata su stati di sollecitazione
corrispondenti. La definizione di stati di sollecitazione corrispondenti `e fondata su
una speciale classe di soluzioni del problema elastico del solido cilindrico tridimensional
How to model blood ow in distensible vessels.
No full textIn this paper, after a brief presentation of the basic ingredients of the theory, we concentrate on the strategy to use two disparate and dimensionally mismatched models: a standard three--dimensional continuum model for the fluid vs our one-dimensional continuum with affine microstructure for the vesse
Electromechanical modeling of anisotropic cardiac tissues
No full textWe model cardiac muscle contractions in the framework of finite elasticity with large distortions and couple a mechanical model with reaction–diffusion equations representing electrophysiological activity. Both models are implemented using anisotropic constitutive relations: we use stress–strain relations for fiber-reinforced materials, and anisotropic diffusion tensors for both the membrane potential and calcium ions. The effects of these choices on the electromechanical behavior are presented and discusse
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