Protection mechanism investigation of a protective coating on magnesium alloy stents via deformation model construction and the simulation of cellular automata.

Abstract

The most significant challenge facing magnesium alloy stents is their ability to withstand complex deformation during their application. To gain a deeper understanding of the impact of stent deformation on the protective capabilities of the coating, this paper presents an amplified stent deformation model. The models were coated with either a low elongation material-Poly(D, L-lactide) (PDLLA) or a high elongation material-Poly(butylene adipate-co-terephthalate) (PBAT), followed by the application of a rapamycin-loaded PLGA as drug-eluting layer. Coating integrity and thickness were examined via scanning electron microscopy (SEM), while electrochemical impedance spectroscopy and long-term immersion tests assessed corrosion behavior on the deformation model. Finite element analysis using Comsol simulated the stress-strain distribution during compression and tension, and cellular automata (CA) models were employed to simulate the corrosion process. The drug release tests were conducted in vitro, and in vivo performance was evaluated through stent implantation in rabbit carotid arteries using optical coherence tomography, SEM, and histological analysis. Results demonstrated that PBAT coatings maintained structural integrity without apparent microcracks after deformation, whereas PDLLA coatings exhibited significant cracking and significantly reduced charge transfer resistance. This reduction in protective performance is observed to occur predominantly in regions of strain concentration with more porosity during the deformation process. CA simulations and immersion tests confirmed slower degradation rates under PBAT. Moreover, PBAT-coated stents achieved larger luminal areas, reduced neointimal formation, and lower restenosis rates compared to PDLLA-coated counterparts in vivo. In conclusion, PBAT coatings offer robust protection against deformation-induced damage and corrosion, representing a promising strategy for enhancing the long-term performance of Mg alloy stents.