In vitro release study of sirolimus from a PDLLA matrix on a bioresorbable drug-eluting stent

Releasing the correct therapeutic drug dose from a bioresorbable drug-eluting stent (DES) is important for inhibiting smooth muscle cell growth, neointimal hyperplasia and in-stent restenosis (ISR). In this study, the in vitro release profiles of sirolimus-in-poly (D, l-lactide) (PDLLA) coatings were investigated under various conditions. First, single-layer, bilayer and various ratios of sirolimus/PDLLA coatings on biodegradable poly (l-lactide) (PLLA) stents and tubes were prepared. There was no apparent delamination or cracking on the stent coating surfaces that had undergone crimping and expansion. Second, the degradation performance of drug-free PDLLA films was investigated to analyse the effects of changes in molecular weight and mass loss. Finally, the in vitro sirolimus release profiles of various coating formulas in phosphate-buffered saline (PBS) were studied by high-performance liquid chromatography (HPLC). The results indicated that the profiles exhibited similar two-phase release kinetics, but the initial release rates were quite different. Moreover, coatings with polyethylene glycol (PEG) additives were prepared to assess their controlled release behaviours. The work reported herein represents a step towards establishing an in vitro release model, which will be verified in future works after comparison with in vivo release profiles.