Biomedical Engineering Reference
In-Depth Information
Figures 13.7-13.9 illustrate that NCM can produce polymeric micelles that
are recoverable in water and hence can be potentially useful for drug delivery.
However, the phase behavior of that early prototype system was not very
practical due to relatively high pressures. Thus, the next objective was to
understand how to reduce the NCM pressure, for example, by optimizing the
solvent composition effects.
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13.4 Optimizing the NCM Solvent
To address this challenge, Green et al.
19
chose trifluoromethane, 1,1,1,2-
tetrafluoroethane, hexafluoroethane, and dimethyl ether as model solvents,
and PEG-b-PCL as a model solute, in which the PCL block was substantially
larger than that used in the previous figures. Figure 13.10 illustrates sample
results for trifluoromethane, in which micelles are found above the CP curve
(the actual MP is beyond the pressure limit). Figure 13.11 illustrates that a new
solvent, dimethyl ether, is not selective enough for PEG-b-PCL to form
Figure 13.12
Pressure-composition phase diagram for PEG-b-PCL (5k-b-11k) in
near-critical mixtures of trifluoromethane and dimethyl ether at
various temperatures. The concentration of polymer in solution was
1 wt%. (Reproduced from Green et al.
19
with permission from the
American Chemical Society.)
