141 research outputs found
Mathematical Modelling of Variable Porosity Coatings for Dual Drug Delivery
In this paper we describe a theoretical mathematical model of dual drug delivery from a durable
polymer coated medical device. We demonstrate how the release rate of each drug may in principle
be controlled by altering the initial loading configuration of the two drugs. By varying the underlying
microstructure of polymer coating, further control may be obtained, providing the opportunity to
tailor the release profile of each drug for the given application
A general model of coupled drug release and tissue absorption for drug delivery devices
In this paper we present a general model of drug release from a drug delivery device and the subsequent transport in biological tissue. The model incorporates drug diffusion, dissolution and solubility in the polymer coating, coupled with diffusion, convection and reaction in the biological tissue. Each layer contains bound and free drug phases so that the resulting model is a coupled two-phase two-layer system of partial differential equations. One of the novelties is the generality of the model in each layer. Within the drug coating, our model includes diffusion as well as three different models of dissolution. We show that the model may also be used in cases where dissolution is rapid or not relevant, and additionally when drug release is not limited by its solubility. Within the biological tissue, the model can account for nonlinear saturable reversible binding, with linear reversible binding and linear irreversible binding being recovered as special cases. The generality of our model will allow the simulation of the release from a wide range of drug delivery devices encompassing many different applications. To demonstrate the efficacy of our model we simulate results for the particular application of drug release from arterial stents
Drug delivery from microcapsules: how can we estimate the release time?
Predicting the release performance of a drug delivery device is an important
challenge in pharmaceutics and biomedical science. In this paper, we consider a
multi-layer diffusion model of drug release from a composite spherical
microcapsule into an external surrounding medium. Based on this model, we
present two approaches that provide useful indicators of the release time, i.e.
the time required for the drug-filled capsule to be depleted. Both approaches
make use of temporal moments of the drug concentration versus time curve at the
centre of the capsule, which provide useful insight into the timescale of the
process and can be computed exactly without explicit calculation of the full
transient solution of the multi-layer diffusion model. The first approach,
which uses the zeroth and first temporal moments only, provides simple
algebraic expressions involving the various parameters in the model (e.g. layer
diffusivities, mass transfer coefficients, partition coefficients) to
characterize the release time while the second approach yields an asymptotic
estimate of the release time that depends on consecutive higher moments.
Through several test cases, we show that both approaches provide a
computationally-cheap and useful measure to compare \textit{a priori} the
release time of different composite microcapsule configurations.Comment: 15 pages, 4 figures, submitte
Non-linear Langevin model for the early-stage dynamics of electrospinning jets
We present a non-linear Langevin model to investigate the early-stage
dynamics of electrified polymer jets in electrospinning experiments. In
particular, we study the effects of air drag force on the uniaxial elongation
of the charged jet, right after ejection from the nozzle. Numerical simulations
show that the elongation of the jet filament close to the injection point is
significantly affected by the non-linear drag exerted by the surrounding air.
These result provide useful insights for the optimal design of current and
future electrospinning experiments.Comment: 11 pages, 6 figures, 1 table. arXiv admin note: text overlap with
arXiv:1503.0469
A general model of coupled drug release and tissue absorption for drug delivery devices
In this paper we present a general model of drug release from a drug delivery device and the subsequent transport in biological tissue. The model incorporates drug diffusion, dissolution and solubility in the polymer coating, coupled with diffusion, convection and reaction in the biological tissue. Each layer contains bound and free drug phases so that the resulting model is a coupled two-phase two-layer system of partial differential equations. One of the novelties is the generality of the model in each layer. Within the drug coating, our model includes diffusion as well as three different models of dissolution. We show that the model may also be used in cases where dissolution is rapid or not relevant, and additionally when drug release is not limited by its solubility. Within the biological tissue, the model can account for non-linear saturable reversible binding, with linear reversible binding and linear irreversible binding being recovered as special cases. The generality of our model will allow the simulation of the release from a wide range of drug delivery devices encompassing many different applications. To demonstrate the efficacy of our model we simulate results for the particular application of drug release from arterial stents
Different regimes of the uniaxial elongation of electrically charged viscoelastic jets due to dissipative air drag
We investigate the effects of dissipative air drag on the dynamics of
electrified jets in the initial stage of the electrospinning process. The main
idea is to use a Brownian noise to model air drag effects on the uniaxial
elongation of the jets. The developed numerical model is used to probe the
dynamics of electrified polymer jets at different conditions of air drag force,
showing that the dynamics of the charged jet is strongly biased by the presence
of air drag forces. This study provides prospective beneficial implications for
improving forthcoming electrospinning experiments.Comment: 12 pages, 6 figure
Modelling functionalized drug release for a spherical capsule
Advances in material design has led to the rapid development of novel
materials with increasing complexity and functions in bioengineering. In
particular, functionally graded materials (FGMs) offer important advantages in
various fields of application. In this work, we consider a heterogeneous
reaction-diffusion model for an FGM spherical drug releasing system that
generalizes the multi-layer configuration to arbitrary spatially-variable
coefficients. Our model proposes a possible form for the drug diffusivity and
reaction rate functions exhibiting fixed average material properties and a drug
release profile that can be continuously varied between the limiting cases of a
homogeneous system (constant coefficients) and two-layer system (stepwise
coefficients). A hybrid analytical-numerical solution is then used to solve the
model, which provides closed-form expressions for the drug concentration and
drug release profiles in terms of generalized Fourier series. The resulting
concentration and mass profiles show how the release rate can be controlled and
continuously varied between a fast (homogeneous) and slow (two-layer) release.Comment: 16 pages, 10 figures, submitte
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