Degradation of poly(L‐lactic acid) coating on permanent coronary metal stent investigated ex vivo by micro Raman spectroscopy

Abstract

Poly(lactic acid) (PLA) is a biodegradable polymer with a variety of applications, such as functional coatings on implants, due to its biodegradability, good biocompatibility and very low toxicity. In this study, the degradation behavior of high molecular weight poly(L‐lactic acid) (L‐PLA), which was used as polymer coating on permanent coronary metal stent, was investigated ex vivo. Poly(methyl methacrylate) (PMMA)‐embedded histological specimens of stented porcine coronary arteries (left anterior descending artery, left circumflex artery and right coronary artery) were used to follow the degradation at various implantation times (6, 12, 24 and 36 months). Micro Raman spectroscopy was applied as an alternative technique for the determination of the residual content of the L‐PLA coating. For this purpose, the PMMA‐embedded cross sections of stented porcine coronary arteries were characterized through a previously developed Raman method for in situ quantitative analysis of PLA in a PMMA matrix. The residual content of L‐PLA coating on the surface of the coronary metal stent was determined through the relative Raman band area ratio of the C–COO stretching band of PLA at 873 cm−1 and the C–O–C symmetric stretching band of PMMA at 813 cm−1. This study demonstrated that Raman spectroscopy provides an alternative, non‐destructive technique for quantification of L‐PLA coating on permanent coronary metal stent in an animal model. The results suggest that the complete absorption of the L‐PLA coating required more than 24 months for the layer thickness applied in this study and that the degradation of high molecular weight L‐PLA in a porcine model is carried out by a hydrolytic degradation through the bulk erosion mode. Copyright © 2017 John Wiley & Sons, Ltd.