Surface Engineered Thromboresistant Vascular Graft as an Arterial Conduit

There is an unmet clinical need for long-term thromboresistant vascular grafts in cardiovascular surgery as conduits for coronary bypass and peripheral vascular substitutes. Currently available small diameter synthetic vascular grafts fail because of rapid blood clotting (thrombosis) at the blood-material interface and occlusion of the graft lumen. We hypothesized that the surface physicochemical properties of the graft (surface charge, surface energy, and porosity) affect the blood clotting process. In this study, we present the fabrication of a synthetic vascular graft (henceforth referred to as zetagraft) with programmable physicochemical and mechanical properties and its in vitro capacity to prevent the blood component adsorption on the graft surface. We demonstrate the ex vivo hemocompatibility and resistance to blood clotting (thromboresistance) by whole blood perfusion studies. We further demonstrate the in vivo thromboresistance of the zetagraft in pig carotid artery replacement model.<br/><br/><b>Methods:</b> We fabricated small diameter zetagrafts (of 2- and 4-mm diameter) with polyvinyl alcohol dissolved in dimethyl sulfoxide by the solvent extraction driven self-assembly strategy using a tubular assembly device. Zetagrafts were characterized for the physicochemical and mechanical properties by FTIR spectroscopy, Micro CT, scanning electron microscopy, confocal fluorescence microscopy, surface pH, and surface energy by water contact angle measurements. Mechanical testing was performed to determine the stretchability and elastic modulus. In-vitro studies for biocompatibility and cell viability were performed on the zetagraft using fibroblast, HUVEC and HASMC cell lines. Ex vivo hemocompatibility and blood component adsorption studies were performed by circulating fresh porcine blood using a peristaltic pump. The zetagrafts were implanted in pig carotid artery replacement model to evaluate its thromboresistance.<br/><br/><b>Results:</b> The zetagraft was soft, uniform, highly stretchable. Laser confocal microscopy and scanning electron microscopy of a cross section of the zetagraft revealed circularly aligned fiber assembly along the graft’s lumen. The polymer fibers (of ~25 µm diameter) were tightly arranged forming a smooth luminal surface with no large spaces or pores. Morphometric analysis by micro-CT confirmed a uniform and smooth luminal surface with a wall thickness of ~1 mm. In this study, we fabricated zetagrafts of different surface charges (–4.2, –2.5, and –1.9 mV) and surface free energies (72.1, 72.9, and 73.5 mJ/m²). Ex vivo blood perfusion with pig whole blood followed by FT-IR analysis revealed no blood protein adsorption on the zetagraft luminal surface while the commercial grafts (Propaten, and Dacron) exhibited significant adsorption of blood proteins as broad peaks at 3500-3000 cm^-1 indicative of –OH and –NH₂ groups and two peaks at 1640 cm^-1 and 1580 cm^-1corresponding to amide I and amide II stretching bands confirming the presence of amide groups. These studies confirmed that the thromboresistance of the zetagraft is attributed to its high surface free energy (73.35 mJ/m²) that facilitates the formation of tightly bound hydrogen bonded water molecular layer on the zetagraft luminal surface. In comparison, PTFE, PEVA, and PET have low surface energies in the range of 19 to 42 mJ/m² exhibited significant adsorption of the blood components due to the absence of a hydrogen bonded water layer.<br/><br/><b>Conclusions:</b> In this study we demonstrated the development of a thromboresistant zetagraft. Currently we are evaluating its long-term thromboresistance in pig carotid artery replacement model. Our results are very promising and zetagraft will provide a novel small diameter vascular graft and thus fulfil an important unmet clinical need.