Biomedical Engineering Reference
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(a)
120
100
80
60
40
in pH 7.4 phosphate buffer
20
in pH 3 HCl
0
0
60
120
Time (min)
180
240
(b)
120
100
80
60
40
in pH 7.4 phosphate buffer
20
in pH 3 HCl
0
0
60
120
Time (min)
180
240
300
Figure 6.14
Release profiles of diclofenac (a) and salicylic acid (b) from washed chitosan micro/nanoparticles in different
media. (From Boonsongrit, Y., Mitrevej, A., and Mueller, B. W. 2006.
Eur J Pharm Biopharm
62: 267-274. With
permission.)
hydrogel to help it achieve the goal [111-113]. Particle-based drug delivery vehicles, that is,
micro/nanoparticles, have a proven capacity for long-term release. As a result, growing
i interest has focused on overcom i ng the i n herent pharmacolog ical lim itat ions of bulk hydro -
gels by coformulating particulate systems into the hydrogel matrix to form composite
hydrogel networks [10]. In the composite hydrogel, apart from the advantages that particles
bring about, micro/nanoparticles can also be sheltered and protected by the bulk hydrogel
from uncontrolled movement [114]. In typical composite systems for drug release, therapeu-
tics can be loaded into micro/nanoparticles prior to hydrogel encapsulation [112,113].
Alternatively, particles can be designed to be charged; drugs with opposite charge are
loaded via electrostatic interactions with particles in a bulk hydrogel. As reported by Tang
et al. recently, a thermosensitive chitosan/PVA hydrogel containing chitosan derivative
nanoparticles with different charges was prepared for delivering propranolol and diclofenac
sodium. They showed that releases of the two drugs were both the fastest with pure hydro-
gels, indicating that the electrostatic effect between nanoparticles and drugs reduced the
burst release and the addition of nanoparticles was helpful in slowing the suitable drug
release (
cf
.
Figure 6.16)
[111].
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