Comparison of the Thrombogenicity of a Bare and Antithrombogenic Coated Flow Diverter in an In Vitro Flow Model

Abstract

Background: Dual antiplatelet therapy is a pre-requisite for flow diverter (FD) implantation. The purpose of this study was to assess the thrombogenicity of the p48 FD, coated with the newly developed phenox Hydrophilic Polymer Coating (p48_HPC, phenox GmbH, Germany) in comparison with uncoated p48 FDs in an in vitro flow model (Chandler Loop).

Methods: p48 and p48_HPC FDs were implanted into silicon tubes filled with whole human blood and incubated at 37 °C under pulsating flow. After 120 min, platelet count was determined in the blood. Platelet activation markers (PAR1) and formation of microparticles were analyzed in a flow cytometer. Fluorescence microscopy of CD42a positive cells and scanning electron microscopy was used to detect adherent platelets on the wire surface.

Results: Platelets in contact with the uncoated p48 FDs are significantly more activated than those incubated with p48_HPC (73 ± 9% vs. 65 ± 6%, p < 0.05) and release more microparticles (1.8 ± 0.5 vs. 1.4 ± 0.4, p < 0.05). The platelet count after 120-min circulation in the Chandler Loop was significantly lower for the uncoated p48 compared to the p48_HPC indicating significantly greater adherence of the platelets to the p48 (71 ± 8% vs. 87 ± 5%, p < 0.05). SEM and fluorescent antibody imaging revealed minimal platelet adherence to the surface of the p48_HPC compared to the uncoated p48.

Conclusion: The pHPC coating significantly reduces thrombogenicity of the p48 FD. This may help to reduce the risk of thromboembolic complications when using these devices. A reduction in antiplatelet therapy may be possible.

Keywords: Antithrombogenic; Chandler loop; Coating; Flow diverter; HPC; p48.

Fig. 1

Schematic representation of the experimental setup (Chandler Loop model). The devices are incubated in rotating tubes in a cell culture incubator at 37 °C

Fig. 2

Thrombocyte activation after 120 min circulation in the Chandler Loop. The cleavage of the thrombin receptor PAR1 is used as an activation marker (A). In B, platelet microparticle release is used as a marker of platelet activation. PAR1 reactivity and microparticle release is shown relative to the control (blood directly after blood sampling). Thrombocyte activation is reduced significantly by the pHPC coating (Mean ± SD, asterisks denote significance at p ≤ 0.05; n = 5; t-test)

Fig. 3

The platelet count after 120-min circulation in the Chandler Loop in percent of control. The “missing” thrombocytes remain in the tube or on the stent. The platelet count of the uncoated p48 is significantly reduced compared to the pHPC-coated p48 (mean ± SD, asterisks denote significance at p ≤ 0.05; n = 5; t-test)

Fig. 4

Representative fluorescence micrographs of uncoated (bare) and pHPC-coated p48 flow diverter stents. The specimens were incubated in whole blood for 120 min in the Chandler Loop under dynamic conditions. Adherent platelets were stained with a CD42a antibody (yellow fluorescence). While the coating almost completely prevents the adhesion of cells on the stent surface (upper row), the uncoated stent has a thick layer of platelets encapsulated inside a fibrin clot (lower row)

Fig. 5

SEM micrographs of pHPC-coated (A + B) and uncoated (C + D) p48 flow diverter stents. The specimens were incubated in whole blood for 120 min in the Chandler Loop under dynamic conditions. Stents and adherent cells were fixated and sputtered with gold. The rectangle indicates the area shown under a higher magnification. While the coating almost completely prevents the adhesion of cells on the stent surface (A + B), the uncoated stent shows clot formation on and between the struts (C + D)