Biomedical Engineering Reference
In-Depth Information
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Figure 13.18
Paclitaxel release from PEG-b-PCL micelles prepared by solvent
evaporation (open circles) and supercritical micellization (squares) into
distilled water at pH 5 7.4 and T 5 37 uC. Error bars represent the
standard deviation of n 5 4 experiments. (Reproduced from Tyrrell et
al.
20
with permission from the American Chemical Society.)
drug that failed to penetrate the core. This would require a sequential
collapse of blocks, which in turn requires a control of the phase behavior
that is simply unavailable by conventional methods, but attainable by the
NCM method.
Tyrrell et al.
21
chose to prove this concept using FDA-approvable blocks,
such as corona-forming PEG, core-forming PCL, and middle-layer-forming
poly(
L
-lactic acid) (PLLA) or poly(
D
,
L
-lactic acid) (PDLLA) or a random
copolymer of PLLA and PDLLA. Figure 13.19 suggests that trifluoro-
methane has a much lower capacity for PCL than for any of the other
homopolymers. In the temperature range of interest, 20-60 uC, PLLA has a
CP above that of PEG, and PDLLA has a CP below PEG. So, if the triblock
were to consist of a PEG block (to form the corona in water), a PCL block (to
form the core), and a middle block of PLLA, a sequential collapse may be
viable.
Such a sequential collapse is illustrated in Figure 13.20. The top plot for PEG-
b-(PCL-co-PDLLA) displays only two transitions: one from homogenous to
