Some of these artificial vessels can last up to 15 years. This type of vessel can sometimes cause clotting if they are too small in diameter. This is because the flexibility between the polymer is different from that of the real vessel. In the case of smaller vessels, copolyurethanes are sometimes used. This material can pulsate better with the real vessel it is attached to.
Polyurethanes contain an amide-ester linkage and can be formed from a diisocyanate and a diol.
Depending on what groups are contained in each monomer, the polyurethane can be glassy and tough or as in this case, very elastic. The polyurethane is then reacted with another monomer to produce a copolyurethane. The task of trying to decide what type of material is needed for these organs is sometimes as difficult as producing the particular polymer itself. Discovering how the body will react with these materials over time will always be a topic of research.