Biomedical Engineering Reference
In-Depth Information
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Figure 13.19
Cloud pressures of PCL, PLLA, PEG, and PDLLA in trifluoro-
methane. The concentrations in solution are 1 wt%. (Reproduced
from Tyrrell et al.
21
with permission from the American Chemical
Society.)
micellar solution, and one from micellar to bulk precipitation, as expected for a
diblock. The bottom plot for the PEG-b-PLLA-b-PCL triblock shows three
distinct transitions. The first transition is from homogenous to micellar state,
due to PCL aggregation. The second transition is from the micellar to another
micellar state, due to PLLA collapse onto the PCL core. The final one is from
micellar to bulk precipitation, due to micelle aggregation. These results for all
temperatures are summarized in Figure 13.21. The solvent composition was
chosen such that the drug CP fell between the micellization and middle block
collapse pressures. Figure 13.22 shows that such a sequential block collapse
indeed produces particles that exhibit very little, if any, burst release. This
confirms the hypothesis that a precise control of block collapse and drug
aggregation, which is virtually impossible with conventional preparation
methods but attainable with the NSM method, can indeed produce particles
made of FDA-approvable blocks that exhibit not only high drug-loading
content and efficiency but also burst-free release.
