Polyurethanes in heart valve replacement

There are three types of prosthetic heart valves  

The main problems related to bioprosthetic heart valves are due to calcification and tissue failure. However, compared to MHVs, these valves offer a physiological flow pattern and require less anticoagulation than mechanical valves. 

The disadvantage of polymeric heart valves is their susceptibihty to biodegradation and mineralization. This has somewhat limited the use of PUR for prosthetic heart valves. 

Different types of biostable PURs have been used in heart valve components, including polyether urethanes (PEUs), polyether urethane ureas (PEUUs), polycarbonate urethane (PCUs), polycarbonate urethane ureas (PCUUs), polycarbonate-based materials that contain polyhedral oligomeric silsequioxane nanoparticles (POSS) (Ghanbari et al., 2010 Kidane et al 2009b), and those that contain polysiloxane soft segments (Bezuidenhout et al 2015). 

PEUs were used since they have excellent hydrolytic stabihty. In the 1980s two types of trileaflet PUR valves made of Biomer (Ethicon) and Lycra Spandex (DuPont) were developed. The Lycra valves showed low regurgitation in vitro, and lasted for one year or more in large animal models, but calcification and thrombosis became evident in growing sheep (Wisman et al., 1982). Calcification was also seen with Biomer valves in juvenile sheep (Hilbert et al., 1987). 

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