Biomedical Engineering Reference
In-Depth Information
4.2.1 Example of drug delivery model for suture
threads
The following example, developed by Perale
et al.
(2009), was performed
on a resorbable loaded polymeric device. The clarity of the mathematical
model confirms the points underlined in this chapter when considering the
irreversibility of drug delivery (Dantzig and Tucker, 2001). This assumption,
in thermodynamic terms, is true in an
in vivo
context where the drug is
immediately consumed by the body, and in fluid clearance. The concentration
of the drug outside the device could be considered as always being equal to
zero, and thus it cannot be treated as an equilibrium problem. A typical drug
delivery scenario consists of three components: a matrix structure, which
does not diffuse, thus having a diffusion coefficient of zero, water from the
external environment which moves inside matrix structure, and the drug, which
usually diffuses from the inner matrix to the external release environment.
The drug is usually entrapped as solid particles within the volume of the
porous polymer. Without loss of generality, drug particles are assumed to
be uniformly scattered in the entire cross-section of the examined device.
This hypothesis can be easily discarded when devices with non-uniform
distribution of the drug particles are under consideration. in that framework,
the drug release mechanism may be described through the following steps
illustrated in Fig. 4.4:
1.
Water diffuses through the polymeric matrix, wetting all its pores and
activating the polymer swelling.
2.
solid drug particles are then wetted by water.
N
particles cm
-3
Diffusion in liquid phase
Solubilisation
[
i
] [
i
]
*
Concentration
Reference volume
d
p
Polymer pore
Polymer matrix
4.4
Schematic representation of the solubilisation of solid drug
particles embedded in polymer matrix. Reprinted with permission
from Elsevier (Perale
et al.
, 2009).
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