Early scaffold strut coverage in ultra-high molecular weight amorphous PLLA sirolimus-eluting bioresorbable scaffolds: impact of strut thickness assessed in normal porcine coronary arteries

Introduction

The first FDA-approved bioresorbable scaffold (BRS) Absorb BVS (Abbott Vascular, USA) demonstrated a higher rate of scaffold thrombosis when compared to current-generation metallic drug-eluting stents (DES) [1]. It is believed that the bulky strut thickness of 156 µm, exceeding nearly twice that of contemporary metallic DES, is responsible for the higher thrombotic potential of this technology [2].
The speed and quality of stent/scaffold strut coverage by tissue are strongly impacted by strut thickness and shape, which influence shear stress and blood flow dynamics, affecting platelet accumulation and endothelial cell growth [3–5]. Regardless of strut height, non-streamlined scaffold struts influence blood flow recirculation and low flow shear rates and prolong particulate residence time [6]. Low endothelial shear stress influences endothelialization rates, and taller strut height induces an environment of procoagulant and pro­inflammatory elements, which can lead to a greater quantity of thrombus and also accelerate turnover of endothelial cells, making re­endothelialization more difficult [7, 8]. Preclinical studies demonstrated that strut thickness influences thrombogenicity, with struts that are < 100 µm having smaller thrombi than struts that are > 100 µm [9]. Therefore, the reduction in strut thickness resulting in improved vascular healing with neointimal strut coverage is a crucial concept in developing new BRS.
In this study we aimed to evaluate the short-term healing response using optical coherence tomography (OCT) following implantation of a new-generation sirolimus-eluting amorphous PLLA-based BRS (Amaranth Medical, USA) with ultra-thin strut (98-µm, AMA-98) and thin strut (115-µm, AMA-115) thickness in porcine coronary arteries.

Material and methods

Device description

Scaffolds used in this study have almost identical ring design and different strut thicknesses: the ultra-thin strut AMA-98, with strut thickness of 98 µm; and the thin strut AMA-115, with strut thickness of 115 µm. The only difference between the 2 versions is a slightly increased surface area coverage at rated burst pressure in AMA-98 when compared to AMA-115 (respectively: 22% vs. 21% for 3.0 mm scaffolds). Both scaffolds were manufactured by the same company (Amaranth Medical, USA) using an ultra-high molecular weight bioresorbable polylactide-based polymer. Devices are coated with a matrix consisting of a 1 :...


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