Biomedical Engineering Reference
In-Depth Information
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Figure 13.16
Cloud pressures of paclitaxel and PEG-b-PCL (5k-b-5k) in near-critical
dimethyl ether. The concentrations of polymer and drug in solution are
1 and 0.3 wt%, respectively.
implies that the drug is still likely to be in solution when the polymer is
precipitated. This leads to a low driving force for the drug to enter into the
micelle core. As expected from this low driving force, the corresponding drug
loading is about 3.3%, as shown in Figure 13.15 on the left, which is slightly
higher than that obtained from the conventional solvent evaporation method.
However, what would happen if the drug CP fell between the MP and the
CP of the polymer? As it turns out, paclitaxel satisfies this requirement with
PEG-b-PCL (5k-b-5k). Since paclitaxel does not dissolve in trifluoromethane
but easily dissolves in dimethyl ether, as shown in Figure 13.16, their mixture
(70% dimethyl ether) allows us to bring the drug CP to the desired pressure
range, between the copolymer CP and MP, as shown in Figure 13.17.
As a result, the drug precipitates from solution while micelles are present,
which should drive it to the micelle core. This higher driving force results in a
much higher drug-loading content, about 12.4%, as is seen from Figure 13.15
on the right. This is a substantial improvement over conventional solvent
evaporation, which yields about 2.6% drug-loading content. However, the
drug
release
profile,
as
seen
in
Figure 13.18,
still
exhibits
burst
release
