Chemical images of the surfaces and the interiors of coatings of rapamycin in poly(lactic-co-glycolic acid) (PLGA) obtained by mass spectrometry and light scattering methods reveal a three dimensional picture of the chemical morphology of drug eluting coatings before, during, and after drug elution. The coating formulations examined ranged from 5 to 50 wt% rapamycin in PLGA with and without a top layer ( capcoat ) of PLGA. Surface sensitive electron spectroscopy for chemical analysis (ESCA) and time-of-flight secondary ion mass spectrometry (TOF-SIMS) indicate that the outer surface of the coatings (without a PLGA capcoat) were drug-rich prior to elution. Upon sputtering with SF5+ ion clusters, TOF-SIMS probed into the coating interior revealing that the thickness of the drug-enriched region on the non-capcoated coatings ranged from 5 to 115 nm. The chemical morphology of the rapamycin/PLGA coatings on stents was determined using scanning confocal Raman microscopy, from the surface through the bulk of the coatings. Images of the coatings on stents show a homogeneous distribution of rapamycin for the coatings with low concentration of drug and more particle-like concentrations of rapamycin for the coating with high concentration of drug. As the drug elution proceeded, images from the interior of the films show rapamycin diffused out of the coating but also became more segregated (particle-like) in the polymer matrix. Optical interferometry measurements of coating thickness suggested that PLGA eroded from the coating during the elution experiment.
Citation: Journal of Controlled Release
Pub Type: Journals
characterization, drug, elution, imaging, stent