scholarly journals Mathematical Model of Macromolecular Drug Transport in a Partially Liquefied Vitreous Humor

2021 ◽  
Author(s):  
Anahid Khoobyar ◽  
Anita Penkova ◽  
Mark S. Humayun ◽  
Satwindar Singh Sadhal
Keyword(s):  
Porous Medium ◽  
Drug Transport ◽  
Three Dimensional ◽  
Building Blocks ◽  
Vitreous Humor ◽  
Convective Transport ◽  
Three Dimensional Model ◽  
Ocular Drugs ◽  
Retinal Region ◽  
Flow Convergence

Abstract The purpose of this study is to investigate the effect of partial liquefaction (due to ageing) of the vitreous humor on the transport of ocular drugs. In our model, the gel part of the vitreous is treated as a Darcy-type porous medium. A spherical region within the porous part of vitreous is in a liquid state which, for computational purposes, is also treated as a porous medium but with a much higher permeability. Using the finite element method, a time-dependent, three-dimensional model has been developed to computationally simulate (using the Petrov-Galerkin method) the transport of intravitreally injected macromolecules where both convection and diffusion are present. From a fluid physics and transport phenomena perspective, the results show many interesting features. For pressure-driven flow across the vitreous, the flow streamlines converge into the liquefied region as the flow seeks the fastest path of travel. Furthermore, as expected, with increased level of liquefaction, the overall flow rate increases for a given pressure drop. We have quantified this effect for various geometrical considerations. The flow convergence into the liquefied region has important implication for convective transport. One effect is the clear diversion of the drug as it reaches the liquefied region. In some instances, the entry point of the drug in the retinal region gets slightly shifted due to liquefaction. While the model has many approximations and assumptions, the focus is illustrating the effect of liquefaction as one of the building blocks towards a fully comprehensive model.

A three-dimensional thermal study of a mercury discharge lamp with double envelope for different orientations

2014 ◽  
Vol 81 (2) ◽  
Author(s):  
Mohamed Bechir Ben Hamida ◽  
Kamel Charrada
Keyword(s):  
Steady State ◽  
Transport Phenomena ◽  
Three Dimensional ◽  
Convective Transport ◽  
Thermal Study ◽  
Mercury Lamp ◽  
Dimensional Model ◽  
Three Dimensional Model ◽  
Discharge Lamp ◽  
Double Envelope

This paper is devoted to study the dynamics of a discharge lamp in different position. As an example of application, we chose the mercury lamp. For this, we realized a three-dimensional model, steady state. After the validation of this model, we used it to reproduce the influence of some parameters that have appeared on major transport phenomena of mass and energy in studying the lamp operating in different positions. Indeed, the pressure and the orientation of the lamp are modified. The effect of convective transport and the accumulation of mercury behind the electrodes are studied.

scholarly journals Potential impact of iodinated replacement compounds CF<sub>3</sub>I and CH<sub>3</sub>I on atmospheric ozone: a three-dimensional modeling study

2010 ◽  
Vol 10 (20) ◽  
pp. 10129-10144 ◽  
Author(s):  
D. Youn ◽  
K. O. Patten ◽  
D. J. Wuebbles ◽  
H. Lee ◽  
C.-W. So
Keyword(s):  
Transport Model ◽  
Stratospheric Ozone ◽  
Vertical Mixing ◽  
Three Dimensional ◽  
Convective Transport ◽  
Atmospheric Ozone ◽  
Dimensional Model ◽  
Three Dimensional Model ◽  
Model Calculations ◽  
The Tropics

Abstract. The concept of Ozone Depletion Potentials (ODPs) is extensively used in policy considerations related to concerns about the effects of various halocarbons and other gases on stratospheric ozone. Many of the recent candidate replacement compounds have atmospheric lifetimes shorter than one year in order to limit their environmental effects, especially on stratospheric ozone. Using a three-dimensional global chemistry-transport model (CTM) of the troposphere and the stratosphere, the purpose of this study is to evaluate the potential effects of several very short-lived iodinated substances, namely iodotrifluoromethane (CF3I) and methyl iodide (CH3I), on atmospheric ozone. Like other chemicals with extremely short lifetimes, the stratospheric halogen loading and resulting ozone effects from these compounds are strongly dependent on the location of emissions. For CF3I, a possible replacement candidate for bromotrifluoromethane (CF3Br), ODPs derived by the three-dimensional model are 0.008 with chemical lifetime of 5.03 days and 0.016 with a lifetime of 1.13 days for emissions assumed to be evenly distributed over land surfaces at mid-latitudes and the tropics, respectively. While this is the first time the ODPs have been evaluated with a three-dimensional model, these values are in good agreement with those derived previously. The model calculations suggest that tropical convection could deliver a larger portion of the gas and their breakdown products to the upper troposphere and lower stratosphere if emission source is located in the tropics. The resulting ODP for CH3I, emitted from mid-latitudes, is 0.017 with lifetime of 13.59 days. Valid simulations of convective transport, vertical mixing and degradation chemistry of CH3I are shown that have good qualitative agreement between the model derived distribution of background CH3I, based on global source emission fluxes from previous studies, and available observations especially in vertical profiles.

scholarly journals Analytical and Computational Modeling of Sustained-Release Drug Implants in the Vitreous Humor

2021 ◽  
Author(s):  
Anahid Khoobyar ◽  
Amin Naghdloo ◽  
Anita Penkova ◽  
Mark S. Humayun ◽  
Satwindar Singh. Sadhal
Keyword(s):  
Fluid Flow ◽  
Sustained Release ◽  
Analytical Model ◽  
Drug Transport ◽  
Transfer Problem ◽  
Vitreous Humor ◽  
Convective Transport ◽  
Time Dependent ◽  
Flow Process ◽  
Dependent Mass

Abstract Sustained ocular drug delivery systems are necessary for patients needing regular drug therapy since frequent injection is painful, undesirable and risky. One type of sustained-release systems includes pellets loaded with the drug, encapsulated in a porous shell that can be injected into the vitreous humor. There the released drug diffuses while the physiological flow of water provides the convective transport. The fluid flow within the vitreous is described by Darcy's equations for the analytical model and Brinkman flow for the computational analysis, while the drug transport is given by the classical convection-diffusion equation. Since the timescale for the drug depletion is quite large, for the analytical model we consider the exterior surrounding the capsule to be quasi-steady and the interior is time dependent. In the vitreous, the fluid-flow process is relatively slow, and meaningful results can be obtained for small Peclet number whereby a perturbation analysis is possible. For an isolated capsule, with approximately uniform flow in the far-field around it, the mass-transfer problem requires singular perturbation with inner and outer matching. The computational model, besides accommodating the ocular geometry, allows for a fully time-dependent mass-concentration solution and also admits moderate Peclet numbers. As expected, the release rate diminishes with time as the drug depletion lowers the driving potential. The predictive results are sufficient general for a range of capsule permeability values and are useful for the design of the sustained-release microspheres as to the requisite permeability for specific drugs.

scholarly journals Discovering the Latest Scientific Pathways on Tissue Spheroids: Opportunities to Innovate

2021 ◽  
Vol 7 (1) ◽  
pp. 331
Author(s):  
Marisela Rodriguez-Salvador ◽  
Baruc Emet Perez-Benitez ◽  
Karen Marcela Padilla-Aguirre
Keyword(s):  
Three Dimensional ◽  
Building Blocks ◽  
Scientometric Analysis ◽  
Three Dimensional Model ◽  
Scientific Publications ◽  
Technology Intelligence ◽  
Innovative Solutions ◽  
Subject Areas ◽  
Tissue Models ◽  
Rapid Transformation

Tissue spheroids consist of a three-dimensional model of cells which is capable of imitating the complicated composition of healthy and unhealthy human tissue. Due to their unique properties, they can bring innovative solutions to tissue engineering and regenerative medicine, where they can be used as building blocks for the formation of organ and tissue models used in drug experimentation. Considering the rapid transformation of the health industry, it is crucial to assess the research dynamics of this field to support the development of innovative applications. In this research, a scientometric analysis was performed as part of a Competitive Technology Intelligence methodology, to determine the main applications of tissue spheroids. Papers from Scopus and Web of Science published between 2000 and 2019 were organized and analyzed. In total, 868 scientific publications were identified, and four main categories of application were determined. Main subject areas, countries, cities, authors, journals, and institutions were established. In addition, a cluster analysis was performed to determine networks of collaborations between institutions and authors. This article provides insights into the applications of cell aggregates and the research dynamics of this field, which can help in the decision-making process to incorporate emerging and innovative technologies in the health industry.

Numerical Modeling of Non-Newtonian Fluid Flow in a Porous Medium Using a Three-Dimensional Periodic Array

1998 ◽  
Vol 120 (1) ◽  
pp. 131-135 ◽  
Author(s):  
Masahiko Inoue ◽  
Akira Nakayama
Keyword(s):  
Porous Medium ◽  
Fluid Flow ◽  
Pressure Drop ◽  
Pressure Gradient ◽  
Newtonian Fluid ◽  
Three Dimensional ◽  
Dimensional Model ◽  
Three Dimensional Model ◽  
Inertia Effects ◽  
Flow Through

Three-dimensional numerical experiments have been conducted to investigate the viscous and porous inertia effects on the pressure drop in a non-Newtonian fluid flow through a porous medium. A collection of cubes placed in a region of infinite extent has been proposed as a three-dimensional model of microscopic porous structure. A full set of three-dimensional momentum equations is treated along with the continuity equation at a pore scale, so as to simulate a flow through an infinite number of obstacles arranged in a regular pattern. The microscopic numerical results, thus obtained, are processed to extract the macroscopic relationship between the pressure gradient-mass flow rate. The modified permeability determined by reading the intercept value in the plot showing the dimensionless pressure gradient versus Reynolds number closely follows Christopher and Middleman’s formula based on a hydraulic radius concept. Upon comparing the results based on the two- and three-dimensional models, it has been found that only the three-dimensional model can capture the porous inertia effects on the pressure drop, correctly. The resulting expression for the porous inertia possesses the same functional form as Ergun’s, but its level is found to be only one third of Ergun’s.

scholarly journals 3D modelling of drug-coated balloons for the treatment of calcified superficial femoral arteries

PLoS ONE ◽  
2021 ◽  
Vol 16 (10) ◽  
pp. e0256783
Author(s):  
Monika Colombo ◽  
Anna Corti ◽  
Scott Berceli ◽  
Francesco Migliavacca ◽  
Sean McGinty ◽  
...  
Keyword(s):  
Drug Concentration ◽  
Vessel Wall ◽  
Drug Transport ◽  
Three Dimensional ◽  
Diffusion Reaction ◽  
Three Dimensional Model ◽  
Femoral Arteries ◽  
Drug Concentrations ◽  
Drug Coated Balloon ◽  
Bound Drug

Background/Objectives Drug-coated balloon therapy for diseased superficial femoral arteries remains controversial. Despite its clinical relevance, only a few computational studies based on simplistic two-dimensional models have been proposed to investigate this endovascular therapy to date. This work addresses the aforementioned limitation by analyzing the drug transport and kinetics occurring during drug-coated balloon deployment in a three-dimensional geometry. Methods An idealized three-dimensional model of a superficial femoral artery presenting with a calcific plaque and treated with a drug-coated balloon was created to perform transient mass transport simulations. To account for the transport of drug (i.e. paclitaxel) released by the device, a diffusion-reaction equation was implemented by describing the drug bound to specific intracellular receptors through a non-linear, reversible reaction. The following features concerning procedural aspects, pathologies and modelling assumptions were investigated: (i) balloon application time (60–180 seconds); (ii) vessel wall composition (healthy vs. calcified wall); (iii) sequential balloon application; and (iv) drug wash-out by the blood stream vs. coating retention, modeled as exponential decay. Results The balloon inflation time impacted both the free and specifically-bound drug concentrations in the vessel wall. The vessel wall composition highly affected the drug concentrations. In particular, the specifically-bound drug concentration was four orders of magnitude lower in the calcific compared with healthy vessel wall portions, primarily as a result of reduced drug diffusion. The sequential application of two drug-coated balloons led to modest differences (~15%) in drug concentration immediately after inflation, which became negligible within 10 minutes. The retention of the balloon coating increased the drug concentration in the vessel wall fourfold. Conclusions The overall findings suggest that paclitaxel kinetics may be affected not only by the geometrical and compositional features of the vessel treated with the drug-coated balloon, but also by balloon design characteristics and procedural aspects that should be carefully considered.

scholarly journals Turbulent Flow through and over a Compact Three-Dimensional Model Porous Medium: An Experimental Study

Fluids ◽  
2021 ◽  
Vol 6 (10) ◽  
pp. 337
Author(s):  
James Kofi Arthur
Keyword(s):  
Porous Medium ◽  
Porous Media ◽  
Turbulent Flow ◽  
Turbulent Flows ◽  
Large Scale ◽  
Three Dimensional ◽  
Compact Model ◽  
Three Dimensional Model ◽  
Filling Fraction ◽  
Flow Through

There are several natural and industrial applications where turbulent flows over compact porous media are relevant. However, the study of such flows is rare. In this paper, an experimental investigation of turbulent flow through and over a compact model porous medium is presented to fill this gap in the literature. The objectives of this work were to measure the development of the flow over the porous boundary, the penetration of the turbulent flow into the porous domain, the attendant three-dimensional effects, and Reynolds number effects. These objectives were achieved by conducting particle image velocimetry measurements in a test section with turbulent flow through and over a compact model porous medium of porosity 85%, and filling fraction 21%. The bulk Reynolds numbers were 14,338 and 24,510. The results showed a large-scale anisotropic turbulent flow region over and within the porous medium. The overlying turbulent flow had a boundary layer that thickened along the stream by about 90% and infiltrated into the porous medium to a depth of about 7% of the porous medium rod diameter. The results presented here provide useful physical insight suited for the design and analyses of turbulent flows over compact porous media arrangements.

scholarly journals Using Cellular Automata as a Basis for Procedural Generation of Organic Cities

2020 ◽  
Vol 5 (12) ◽  
pp. 116-120
Author(s):  
Melek B. Temuçin ◽  
İlker Kocabaş ◽  
Kaya Oğuz
Keyword(s):  
Cellular Automata ◽  
Computer Games ◽  
Three Dimensional ◽  
Building Blocks ◽  
Three Dimensional Model ◽  
Procedural Content Generation ◽  
Fractal Properties ◽  
Heterogeneous Structures ◽  
Virtual City ◽  
The City

Procedural content generation (PCG) methods are commonly employed in computer games, simulations, and other related industries. While these methods are used for levels, terrains, stories and missions, their usage for procedural city generation is relatively rare because cities are heterogeneous structures with different components such as roads, layouts and buildings that depend on and affect each other. Additionally, ancient cities grew organically to areas that are safe and to those that provide food and water. This resulted in cities that do not have apparent regular patterns, such as rectangular building blocks. We propose an approach that uses cellular automata (CA) that generates clusters of areas. The CA is repeated for each cluster to hierarchically create different levels of the city. This procedure creates an organic city layout with fractal properties. The layout specifies the building blocks, main roads, and foliage. We also present a set of methods that can transform this layout into a three-dimensional model of the city. The results are promising; cities can be created in under a minute with minimal required input, and the resulting virtual city looks organic, rather than an algorithmic layout that has repeating patterns.  

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