Recent Developments in Lyotropic Liquid Crystals as Drug Delivery Vehicles - Self-Assembled Supramolecular Architectures: Lyotropic Liquid Crystals - page 229

(a) (b)

100

0.6
0.5
0.4
0.3
0.2
0.1
0

80

60

40

20

0

0 5 10

Time (h)

15 20 25

Na-DFC RALA PEN NONA

Figure 8.10 (a) Na-DFC cumulative skin permeation quantity vs. time in the different
systems: control (Na-DFC only) ( ), RALA - loaded ( ), PEN - loaded (

), and NONA-
loaded ( ). (b) The calculated permeability coeffi cient ( K p ) based on the diffusion rate
of 1.0 wt % Na-DFC via Franz diffusion cells as affected by the different peptides
added to the mesophase (Cohen-Avrahami et al., 2011).

Δ

The Higuchi diffusion equation was applied to analyze Na-DFC release
from the examined mesophases. The Higuchi model implies that drug release
is primarily controlled by diffusion through the matrix and can be described
by the following equation:

QD ACCt = [ ( 2 − )] /

12

m d d

where Q is the mass of drug released at time t and is proportional to the appar-
ent diffusion coeffi cient of the drug in the matrix, D m ; the initial amount of
drug in the matrix, A ; and the solubility of the drug in the matrix, C d . The slope
of a linear fi t of the data from this plot is proportional to the “apparent diffu-
sion coeffi cient” for the drug in the matrix and permits preliminary assessment
of diffusion as the primary means of drug release from the correlation coef-
fi cient for the linear fi t and also as a means to compare the diffusion of a drug
from the different matrices into the release medium. The linearity of the plots
was found to be

0.95 for all CPPs, indicating the existence of a diffusion-
controlled transport mechanism (Fig. 8.11). The slope was the greatest for the
blank system, 2.8 h − 1/2 , and it decreased to 2.0, 1.3, and 1.2 in the PEN, NONA,
and RALA systems, respectively.
The “blank” systems released the highest amounts of Na-DFC, and the
release from the CPP-loaded systems was much lower. The order of Higuchi
slopes was exactly the same; blank

>

> PEN > N O N A > RALA, and their values

were 3.0, 0.9, 0.7, and 0.6 h − 1/2 , respectively.
Considering the Na-DFC's amphiphilic nature and the H II mesophase
structure, in which the aqueous phase is tightly packed within the lipid
structure, with the limited accessibility to the surrounding media, one can
assume that the drug diffusion out of the mesophase occurs through the lipo-
philic oily regions. The CPPs incorporated within the mesophase slowed the