Scanning electron microscopic assessment of the biodegradable coating on expanded biolimus-eluting stents

Aims: Biodegradable coatings on drug-eluting stents (DES) may help to avoid adverse long-term effects of DES such as late/very late stent thrombosis which is partly attributed to durable polymers. As the post-expansion morphology of biodegradable coatings is greatly unknown, we investigated the polylactic acid coating on biolimus-eluting BioMatrix stents. Methods and results: Scanning electron microscopy (SEM) was used to carefully examine five 3.5 mm stents following expansion at 6-14 atm (maximum 7% overstretch). SEM examination demonstrated only mild cracks of the coating after stent expansion at 6 atm. An increase in expansion pressure, associated with mild stent overstretch, resulted in more severe cracks. Lifting of the coating together with few sites of partial detachment of fragments was noticed after stent expansion in water at 14 atm; these irregularities further increased after aggressive oversized partial postdilatation with a 5.0 mm non-compliant balloon with additional secondary cracks. Conclusions: SEM assessment suggests a relatively low elasticity of the biodegradable coating on BioMatrix stents. At nominal pressure, stents showed predominantly mild cracks of the coating, while cracks increased after slight overstretch. Aggressive overexpansion of the stent, such as sometimes required in left main bifurcation stenting, worsened cracks and led to some detachment of fragments of the coating in vitro.