Cluster Secondary Ion Mass Spectrometry (cluster SIMS) employing an SF5+ polyatomic primary ion sputter source in conjunction with a Bi3+ analysis source was used to obtain 3-dimensional molecular information in polymeric-based drug eluting stent (DES) coatings. The formulations of the coatings varied from 0% to 50% (w/w) rapamycin drug in poly(lactic-co-glycolic acid) (PLGA) and were prepared both on MP35N metal alloy coupons and bare metal stents. All cluster SIMS depth profiles obtained indicated a drug-enriched surface region, followed by a drug-depletion region, and finally a constant bulk composition region, similar to previous data obtained in polymeric blend systems. The overlayer thickness was determined to increase with increasing rapamycin content. Sample temperature was determined to play an important role in the resulting depth profiles, where it was shown that the best profiles were obtained at low temperatures (-100 oC). At these temperatures, molecular signals typically remained constant through the entire depth of the film (~6.5 m) in some cases, as opposed to the typical (1-2) m depth limit which is achievable at room temperature. The 3-D imaging capabilities of cluster SIMS were successfully demonstrated and indicated a significant amount of subsurface domain formation in the 25% and 50% rapamycin samples, but not in the 5% sample, which was homogeneous. These results clearly illustrate the utility of cluster SIMS for probing the 3-D structure in polymeric based drug delivery devices.
Citation: Analytical Chemistry
Pub Type: Journals
Bi, cardiac, cluster SIMS SF5+, depth profile, drug delivery, polymers, SIMS, stent, TOF-SIMS