Physical testing of elastomers for cardiovascular applications

There are presently no short-term in vitro fatigue tests available that can predict long-term in vivo performance of elastomers in physiological environments. Thus, the introduction of new and better elastomers for cardiovascular applications is hampered in the development stage by lack of data about which materials should be commercialized. After development, new materials are also slow to be used because of the lack of comparative data on current elastomers. Thus, short-term fatigue tests are being developed in three U.S. laboratories. In our laboratory, a wide variety of fatigue tests has been conducted using a constant strain fatigue test machine. In most of these fatigue tests, the strain is increased daily until failure occurs. Although blood is generally considered to be a very corrosive environment, our tests indicate that it actually extends the fatigue life of elastomers, compared with air or water environments. A combination of fatigue tests using both cut-initiated and uncut test specimens appears to provide the most predictive information.