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Abstract
Introduction Endovascular flow diverters (FDs) and stents, comprised of shape memory (i.e. Nitinol) or cobalt alloys have limited long-term biocompatibility. Nitinol can leach genotoxic and allergy-inducing nickel ions. Current nitinol and metal alloys also exhibit inconsistent endothelialization across the aneurysm neck, often resulting in delayed aneurysm occlusion.
PPODA-QT (NeuroCURE®) is a biocompatible polymer under development for endosaccular treatment of intracranial aneurysms. ISO-certified biocompatibility testing confirms NeuroCURE exhibits superior hemocompatibility (prevents thrombosis) and promotes continuous endothelial growth over the aneurysm neck within the first 6-months. In this study, we chemically bound a monolayer of PPODA to Nitinol wires to enhance mechanical stability and biocompatibility.
Materials and Methods Oxygen-argon plasma treatment was used to prepare the surface of nitinol wires. Silanization with SH-PEG-Silane functionalized the surface to improve polymer adhesion. Inductively coupled plasma mass spectrometry (ICP-MS) and scanning electron microscopy (SEM) were used to verify presence of the silane layer.
Surface-modified wires were coated by running a basic solution containing PPODA over the wire surface (figure 1a). The terminal thiol groups of the silane reacted with PPODA (Michael addition reaction - figure 1b). ICP-MS and SEM were used to evaluate polymer continuity and thickness. Polymer properties were then compared to parylene, an established polymer control coating applied via vapor deposition.
The integrity of PPODA and parylene coatings was evaluated, via a DMA-rheometer (TA Instruments) in the Bioengineering Devices Lab (BDL) at Northern Arizona University (NAU). Shear, wire-on-wire delamination, and bending integrity at physiologically-relevant forces and shear rates were assessed, and SEM verified potential wire-polymer delamination effects.
Results and Discussion SEM images showed variation in continuity among the different surface coatings and the controls (with or without surface modification, PPODA versus parylene). Mechanical testing suggested significant variations in adhesion of different coatings, helping to optimize the coating technique. Future work will finalize coating optimization and assess biocompatibility of control (uncoated) versus coated wires for in vitro endothelial cell growth, implantation effects, hemocompatibility, and metal ion leaching (Time-of-Flight Secondary Ion Mass Spectrometry - ToF-SIMS).
Conclusion PPODA polymer coatings can improve biocompatibility and prevent thrombosis on FDs and stents by pre-coating wires for braiding or post-coating laser-cut stent devices. Future work will compare coating integrity and biocompatibility to established devices (i.e Pipeline Shield® and Fred-X®). Materials like PPODA may provide FDs and stents with a mechanically stable scaffold coating that promotes continuous re-endothelialization over an aneurysm neck, which can eliminate thrombosis and reduce recanalization rates.
SH-PEG-Silane and PPODA bound to a nitinol wire surface. Figure la is an SEM image of a nitinol wire with these polymers attached and Figure 1b is a graphic depiction of this attachment
Disclosures S. Robertson: 5; C; Northern Arizona University. W. Merritt: 1; C; SNIS Young Investigator Research Grant. 4; C; Aneuvas Technologies, Inc. 5; C; Aneuvas Technologies, Inc. T. Becker: 1; C; SNIS Young Investigator Research Grant. 2; C; United Biologics. 4; C; Aneuvas Technologies, Inc. 5; C; Northern Arizona University. A. Ducruet: 2; C; Medtronic, Penumbra, Oculus, Stryker, Balt, Koswire. 4; C; Aneuvas Technologies, Inc. 5; C; Barrow Neurological Institute.