Flow-Directed Loading of Block Copolymer Micelles
with Hydrophobic Probes in a Gas–Liquid Microreactor
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Abstract
We investigate the loading efficiencies
of two chemically distinct
hydrophobic fluorescent probes, pyrene and naphthalene, for self-assembly
and loading of polystyrene-<i>block</i>-poly(acrylic acid)
(PS-<i>b</i>-PAA) micelles in gas–liquid segmented
microfluidic reactors under different chemical and flow conditions.
On-chip loading efficiencies are compared to values obtained via off-chip
dropwise water addition to a solution of copolymer and probe. On-chip,
probe loading efficiencies depend strongly on the chemical probe,
initial solvent, water content, and flow rate. For pyrene and naphthalene
probes, maximum on-chip loading efficiencies of 73 ± 6% and 11
± 3%, respectively, are obtained, in both cases using the more
polar solvent (DMF), an intermediate water content (2 wt % above critical),
and a low flow rate (∼5 μL/min); these values are compared
to 81 ± 6% and 48 ± 2%, respectively, for off-chip loading.
On-chip loading shows a significant improvement over the off-chip
process where shear-induced formation of smaller micelles enables
increased encapsulation of probe. As well, we show that on-chip loading
allows off-chip release kinetics to be controlled via flow rate: compared
to vehicles produced at ∼5 μL/min, pyrene release kinetics
from vehicles produced at ∼50 μL/min showed a longer
initial period of burst release, followed by slow release over a longer
total period. These results demonstrate the necessity to match probes,
solvents, and running conditions to achieve effective loading, which
is essential information for further developing these on-chip platforms
for manufacturing drug delivery formulations