Biomedical Engineering Reference
In-Depth Information
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Figure 9.13
Schematic illustration of complex micelles with thermally induced PEG
channels
for
controlled
drug
release
and
protecting
PLA
against
enzymatic degradation.
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PNIPAM content. A decreased ibuprofen release rate with increasing
PNIPAM content in the micelle shell was observed, which was ascribed to
an enhanced retardation effect on drug diffusion from the micelle core by the
collapsed PNIPAM and decreased amounts of PEG channels for drug release.
Lin et al.
18
have reported a new type of complex micelle with a
poly(propylene oxide) (PPO) core and a mixed shell consisting of poly(
L
-
glutamic acid) (PLGA) and PEG for drug delivery applications, as illustrated
in Figure 9.14. The micelles were prepared through a co-micellization of
PLGA-b-PPO-b-PLGA and PEG-b-PPO in water. In acidic conditions, PLGA
undergoes a transformation from water-soluble random coils to a water-
insoluble a-helix, leading to microphase separation in the mixed micelle shell.
The PLGA chains collapse on the surface of the PPO core, forming patchy or
continuous domains that are impermeable for drugs. The PEG chains with
higher solubility connect the micelle core and the outer milieu, serving as
channels for a rapid diffuse of loaded drugs. The drug release profile can be
manipulated by tuning the composition of the mixed shell. An accelerated drug
release rate is observed at the initial stage of increasing the PLGA in the mixed
shell, which is suggested to be due to an increased stress of collapsed PLGA
chains on the micelle core, which give rise to a core distortion inducing a
leakage of loaded drugs. A higher content of PLGA chains can generate a
higher stress force, but results in a smaller domain of PEG channels. Above
Figure 9.14
Schematic representation of the release mechanism proposed for the
PLGA-b-PPO-b-PLGA/PEG-b-PPO drug-loaded complex micelles.
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