Surface characterization of poly(lactic acid)/everolimus and poly(ethylene vinyl alcohol)/everolimus stents

Abstract

Two model drug eluting stents of poly(lactic acid) (PLA)/everolimus and poly(ethylene vinyl alcohol) copolymer (EVAL)/everolimus have been investigated using complementary surface analysis techniques including AFM, XPS, and ATR-IR to assess their structure and its relation to drug release. Different surface morphologies were observed for these stents, with phase separation evident on the PLA coating and a homogeneous system for the EVAL-based coating. This indicates a potentially different drug distribution for the different stents, although both showed a surface enrichment of the drug compared to the bulk. Dissolution studies for PLA/everolimus stents showed an immediate loss of drug from the surface as well as a longer term polymer matrix erosion. The EVAL/everolimus stent also displayed a loss of drug from its surface, but an intact surface after 28 days in dissolution media. These data are discussed in relation to the different release mechanisms occurring in the stents.

Stent elution rate determines drug deposition and receptor-mediated effects

“…Subsequently, imaging studies of CYPHER ® Stent coatings [20,21] and similar conformal coated DES [22–24] explained that drug distribution can deviate from the idealized layered designs due to the influence of mixing and drying that occurs during coating manufacture. Specifically, images of the coatings revealed significant concentrations of dispersed drug in the top-coat [21,24–26] that are inconsistent with the reservoir/membrane description and explain observations of early drug bursts from CYPHER ® Stents and other conformal coated stents[5,24,27]. In light of these studies, we idealize CYPHER ® Stent coatings as monolithic films that contain two pools of dispersed drug, one that is surface-connected and elutes through a percolating network of drug filled pores, and another that is embedded within the matrix and diffuses more slowly through the percolating polymer phase.…”

The stability of solid dispersions of felodipine in polyvinylpyrrolidone characterized by nanothermal analysis

“…The darker phase indicates more energy lost by the vibrating AFM cantilever, which can be due to, for example, increased probe-sample contact area, a softer surface or a more adhesive interaction compared to the brighter phase (Chen , 1998). Such phase imaging has been used extensively in the characterization of pharmaceuticals, for example in the identification of polymorphic forms (Danesh et al, 2000), to study the variations in the physico-mechanical properties of salbutamol sulfate crystals due to milling (Begat et al, 2003) and drug enriched regions within a polymeric coating of a drug eluting stent (Wu et al, 2010).…”

Volatile Acid-Solvent Evaporation (VASE): Molecularly Homogeneous Distribution of Acyclovir in a Bioerodable Polymer Matrix for Long-Term Treatment of Herpes Simplex Virus-1 Infections

“…Because of its presumably local targeting that avoids the need for gut absorption, ACV administered by these devices would lead to a lower daily dose and increased bioavailability. With the homogeneity of the novel VASE-created devices, we expect surface erosion instead of bulk erosion, causing improved stability, longevity of the vehicle, and improved kinetics of drug release [ 36 ].…”