NMP 2008
 |
Greg
Haugstad |
Characterization
Facility |
Probing Segregation in Polymer-Drug
Coatings with Advanced AFM and Confocal Raman Microscopy
Greg Haugstad, Charfac, U of MN and Klavs Wormuth, Surmodics
We report ongoing methodological developments
in digital pulsed force mode (D-PFM) AFM and confocal Raman microscopy
(and light and electron microscopy)
of model coatings containing the drug dexamethasone dispersed in poly(butylmethacrylate)
(PBMA), PBMA/poly(laurel methacrylate) (PLMA) blends, and polylactide (PLA).
Efforts include (1) direct comparison of the same sample regions with multiple
techniques; (2) comparing drug-polymer segregation in microsprayed versus
spin-cast coatings; and (3) water-immersion imaging for /in situ/ studies
of drug mobility and release. The latter study of dexamethasone/PBMA reveals
the rapid formation (seconds to minutes) of nanoscale surface holes matching
the size of protrusions in the as-cast films; the deepening and broadening
of these holes over a time frame of tens of minutes; the growth of subsurface
microscale agglomerates (i.e., pushing the surface up) over a period of
several hours; and the replacement of most of these agglomerated domains
by depleted regions (i.e., excess volume becoming reduced volume), over
~15 hours.