Environmental Digital Pulsed Force Mode AFM in Biomedical Coatings Research
G. Haugstad, K. Wormuth
University of Minnesota, US
Keywords: AFM, drug elution, Raman spectroscopy, polymer, coating
Abstract:We report ongoing methodological developments using Digital Pulsed Force Mode AFM of model coatings containing the drug dexamethasone dispersed in polylactide (biodegradable), poly(butylmethacrylate) (PBMA), and PBMA/poly(laurel methacrylate) (PLMA) blends. Studies include (1) multi-technique analyses, understanding D-PFM AFM results in conjunction with electron, light and confocal-Raman microscopy; (2) comparing drug-polymer segregation in microsprayed and spin-cast coatings, to examine kinetic differences in coating application (i.e., of solvent evaporation); (3) aqueous AFM of drug elution, in conjunction with conventional drug-release profiles; and (4) elevated temperature and humidity as “knobs” to yield material contrast and mobilize drug. Corresponding results include (1) the identification of SEM e-beam modifications, and distinctly different surface vs. bulk (AFM vs. Raman) drug segregation, important to burst vs. longer term release; (2) dramatic differences in drug segregation in sprayed vs. spin-cast coatings; (3) rapid formation of nanoscale surface holes during burst phase, and subsurface drug aggregation then release over much longer times; (4) both humidity- and temperature-induced drug crystallization in the vicinity of rubbery polymer domains in which the drug is less miscible. We conclude that environmental D-PFM AFM is an extraordinarily powerful tool to assess myriad issues within drug-eluting coatings research and development.