Biomedical Engineering Reference
In-Depth Information
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Figure 13.17
Cloud pressures of paclitaxel, PEG-b-PCL (5k-b-5k), and mixture and
micellization pressure (MP) of PEG-b-PCL (5k-b-5k) in near-critical
dimethyl ether/trifluoromethane (70/30) mixture. The concentrations
of polymer and drug in solution are 1.5 and 0.15 wt%, respectively.
The arrows indicate the pressure/time profile of the micellization/
depressurization
process
used
to
recover
drug-loaded
micelles.
al.
20
(Reproduced
from
Tyrrell
et
with
permission
from
the
American Chemical Society.)
characteristic of conventional approaches, which posed a new challenge for
NCM.
13.6 NCM: A Remedy for Burst Release?
Tyrrell et al.
21
attempted to address this burst release challenge using a triblock
copolymer. A simplistic idea underpinning the conventional methods is that,
when diblock micelles are formed in liquid solution, all the drug will be
encapsulated in the core of the micelle due to the core-forming block's higher
affinity for the drug. As suggested by Tyrrell et al.,
21
for all such conventional
methods, much of the drug can be deposited on the outside of the core, which
can lead to burst release.
By contrast, a triblock micelle, if made synchronously with drug
precipitation, forms a middle layer that can coat and hence protect the
