Biomedical Engineering Reference
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conditions demonstrated a Fickian sustained release over 2
weeks. The Flory-Huggins interaction parameter is a useful tool
to understand thermodynamic affinity of a drug for a micelle core.
As the interaction parameter would likely decrease with increased
molecular weight of the PCL block[61], it is likely that DOX has a
higher value interaction parameter than cucurbitacin with PCL.
O
O
O
H
N
O
17
O
O
O
13
Br
N
N
O
H
O
H
O
O
OH
OH
O
O
a
b
OCONH
2
OCONH
2
Figure 3.3
(a) Geldanamycin, and its (b) bromoester prodrug, GA
17
¢
C16Br.
3.2.3
Drug Delivery from Triblock Copolymer Micelles of
PEO and PCL Blocks
The first triblock PCL-PEO-PCL micelles used as a delivery vehicle
were used to characterize the drug loading capacity and release of
the model drug clonazepam [62]. Three triblock copolymers were
investigated with each PCL chain being 2.4, 3.8, or 8.5 kDa and the
PEO block of 8 kDa was constant among this series. The synthesis and
preparation of the triblock copolymer micelles was similar to that
of diblock PEO-PCL micelles, except the initiation of polymerization
occurred on each end of the PEO chain. The loading efficiency of
clonazepam was shown to range from 12-26% depending on the
initial organic solvent. As expected the loading efficiency increased
with PCL block length. Also similar to the diblock PEO-PCL micelles,
these triblock micelles had CMC's on the order of 10
-7
-10
-8
M
and were 20-30 nm in diameter. Clonazepam was released in a
sustained Fickian manner over a period of 4 days. Similar release
behavior has been seen in other triblock micelles of PEO, PCL,
and PVL blocks with nimodipine [63], indomethacin [64], and 4
¢
-
demethylepipodophyllotoxin (DMEP) [65]. Although the triblock
micelles have larger lipophilic cores, the drug loading efficiencies,
capacities, and release behavior are not substantially improved
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