Background and aim of the study: A novel trileaflet polymer valve, which is a composite design of a biostable and biocompatible polymer poly(styrene-block-isobutylene-block-styrene) (SIBS) with an embedded reinforcement polyethylene terephthalate (PET) fabric, is being developed with the intention of providing a valve that has low thrombogenicity, high durability and favorable hemodynamic performance. The study aim was to investigate the biocompatibility and performance of this SIBS valve prototype under physiological loading conditions similar to humans, using a large-animal model.
Methods: Four SIBS valves (two with surface modification using dimyristoyl phosphatidylcholine, DMPC), and two commercial Magna tissue valves, were implanted into sheep. Hemodynamic and blood chemistry measurements were performed periodically during the postoperative period. The explanted SIBS valves were extensively evaluated using macroscopic, histological, radiographical and scanning electron microscopy/energy-dispersive spectroscopy analysis.
Results: Three animals, one with the DMPC-coated SIBS valve, and two with the Magna valves, reached the end of the study in satisfactory clinical condition, and were euthanized after 20 weeks. The other three animals (two with SIBS valves, one with a DMPC-coated SIBS valve) died at 6, 6.5, and 10 weeks due either to material failure or myocardial infarction. The explanted valves exhibited stent deformation and cracks on the leaflets, which exposed the underlying PET fabric and resulted in severe blood and tissue reactions. Extrinsic calcification was identified on the leaflets, and was associated with the regions of surface cracks.
Conclusion: The SIBS valve failed in animal testing because of material failure and calcification. The physical properties of SIBS must be improved in order to provide the structural integrity required for long-term in-vivo use in the form of a heart valve.