Abstract
We report on the local microenvironment surrounding three small fluorescent
probe molecules (pyrene, [6-propionyl-2-(<i>N</i>,<i>N</i>-dimethylamino)
naphthalene] (PRODAN), and
[4-(dicyanomethylene)-2-methyl-6-(4dimethylaminostyryl)-4<i>H</i>-pyran] (DCM))
when they are sequestered at low concentration within thin biodegradable films
formed from poly( L lactic acid) (PLLA) and Pluronic P104 blends. Despite each probe
molecule being neutral, they sense and report from much different microenvironments
in comparison to each other. Specifically, the non-polar pyrene probe senses a
slightly more polar microenvironment as the PLLA content in the polymer blend
increases. In contrast, the polar PRODAN and DCM probes sense less polar
microenvironments as the PLLA content within the polymer blend increases.
Time-resolved fluorescence intensity decay experiments on pure PLLA films reveal
that each probe molecule encounters significant heterogeneity. Pyrene emits
simultaneously from three discrete microenvironments. This is consistent with pyrene
molecules reporting from crystalline, amorphous-crystalline intermediate, and
amorphous regions. PRODAN and DCM appear to emit from a continuum of
microenvironments. These results have ramifications on the performance of
biodegradable drug delivery platforms loaded with small drug molecules.
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