Examinando por Autor "Simon, L."

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    The development of a peak-time criterion for designing controlled-release devices
    (ELSEVIER SCIENCE BV, 2016-08-25) Simon, L.; Ospina, J.; Simon, L.; Ospina, J.; Universidad EAFIT. Departamento de Ciencias; Lógica y Computación
    This work consists of estimating dynamic characteristics for topically-applied drugs when the magnitude of the flux increases to a maximum value, called peak flux, before declining to zero. This situation is typical of controlled- released systems with a finite donor or vehicle volume. Laplace transforms were applied to the governing equations and resulted in an expression for the flux in terms of the physical characteristics of the system. After approximating this function by a second-order model, three parameters of this reduced structure captured the essential features of the original process. Closed-form relationships were then developed for the peak flux and time-to-peak based on the empirical representation. Three case studies that involve mechanisms, such as diffusion, partitioning, dissolution and elimination, were selected to illustrate the procedure. The technique performed successfully as shown by the ability of the second-order flux to match the prediction of the original transport equations. A main advantage of the proposed method is that it does not require a solution of the original partial differential equations. Less accurate results were noted for longer lag times. (C) 2016 Elsevier B.V. All rights reserved.
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    Dynamics of an Electrochemical Biosensor for the Detection of Toxic Substances in Water
    (SPIE-INT SOC OPTICAL ENGINEERING, 2016-01-01) Simon, L.; Ospina, J.; Simon, L.; Ospina, J.; Universidad EAFIT. Departamento de Ciencias; Lógica y Computación
    A proposed analytical method focuses on electrolyte transport to the electrode of an electrochemical cell. The recombinant Escherichia coli whole-cell biosensor detects toxicity in water based on a set of biochemical reactors. Previous contributions elucidated the kinetics of product formation and validated a mathematical model for its diffusion in the chamber. This work introduces an approach to investigate the dynamics of the probe using Laplace transforms and an effective time constant. The transfer function between the electrolyte production and the total current revealed a faster response for larger electrode radii. Both the first-order and effective time constants increased with the chamber height and radius. Separation of variables yields closed-form solutions and helps estimate the kinetics of p-aminophenol generation. When the bacteria were exposed to phenol concentrations of 1.6, 8.3 and 16 ppm, the corresponding overall rate constants were 5.11x10(-7), 1.13x10(-6) and 1.99x10(-6) (product concentration unit/s(2)), respectively. In addition to parameter estimation, the method can be applied to perform sensitivity analysis and aid manufacturers in meeting design specifications of biosensors.
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    On the effusion time of drugs from the open pore of a spherical vesicle
    (ELSEVIER SCIENCE BV, 2016-06-01) Simon, L.; Ospina, J.; Simon, L.; Ospina, J.; Universidad EAFIT. Departamento de Ciencias; Lógica y Computación
    Solute permeation through a spherical liposomal vesicle was analyzed using Fick's second law and a mixed Neumann-Dirichlet boundary condition. The first-principles approach was necessary to help calculate the effusion time of a medication through a pore located on the surface of the device. An infinite series of Bessel functions represented the concentration in the Laplace domain. This method yielded closed-form expressions for the characteristic time and the Laplace-transformed fraction of drug released, which was approximated by the first term of the series. The time constant was inversely proportional to the diffusion coefficient in the system and decreased as the pore size increased. It took 4 times the effusion time to unload nearly ninety-eight percent of the pharmaceutical ingredient. (C) 2016 Elsevier B.V. All rights reserved.
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    Prediction of in-vivo iontophoretic drug release data from in-vitro experiments-insights from modeling
    (ELSEVIER SCIENCE INC, 2015-12-01) Simon, L.; Ospina, J.; Ita, K.; Simon, L.; Ospina, J.; Ita, K.; Universidad EAFIT. Departamento de Ciencias; Lógica y Computación
    A strategy was developed to predict in-vivo plasma drug levels from data collected during in-vitro transdermal iontophoretic delivery experiments. The method used the principle of mass conservation and the Nernst-Planck flux equation to describe molecular transport across the skin. Distribution and elimination of the drug in the body followed a one- or two-compartment open model. Analytical expressions for the relaxation constant and plasma drug concentration were developed using Laplace transforms. The steady-state dermal flux was appropriate for predicting drug absorption under in-vivo conditions only when the time constant in the skin was far greater than its value in the blood compartment. A simulation study was conducted to fully assess the performance of estimations based on the equilibrium flux approximation. The findings showed that the normalized integral of squared error decreased exponentially as the ratio of the two time constants (blood/skin) increased. In the case of a single compartment, the error was reduced from 0.15 to 0.016 when the ratio increased from 10 to 100. The methodology was tested using plasma concentrations of a growth-hormone releasing factor in guinea pigs and naloxone in rats. © 2015 Elsevier Inc. All rights reserved.
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    A three-dimensional semi-analytical solution for predicting drug release through the orifice of a spherical device
    (ELSEVIER SCIENCE BV, 2016-07-25) Simon, L.; Ospina, J.; Simon, L.; Ospina, J.; Universidad EAFIT. Departamento de Ciencias; Lógica y Computación
    Three-dimensional solute transport was investigated for a spherical device with a release hole. The governing equation was derived using the Fick's second law. A mixed Neumann-Dirichlet condition was imposed at the boundary to represent diffusion through a small region on the surface of the device. The cumulative percentage of drug released was calculated in the Laplace domain and represented by the first term of an infinite series of Legendre and modified Bessel functions of the first kind. Application of the Zakian algorithm yielded the time-domain closed-form expression. The first-order solution closely matched a numerical solution generated by Mathematica (R). The proposed method allowed computation of the characteristic time. A larger surface pore resulted in a smaller effective time constant. The agreement between the numerical solution and the semi-analytical method improved noticeably as the size of the orifice increased. It took four time constants for the device to release approximately ninety-eight of its drug content. © 2016 Elsevier B.V. All rights reserved.