An in vivo method for testing hemocompatibility of materials used in prosthetic heart valves

An in vivo method for testing hemocompatibility of materials used in mechanical heart valves was developed.

Discs of test materials were glued to specially designed plastic (Delrin) buttons and implanted into the superior and inferior venae cavae of sheep through a right thoracotomy. The button and disc had such configuration that the blood flow was minimally disturbed. Up to four different materials could be tested simultaneously in each animal: two in superior vena cava and two in inferior vena cava. The materials and their respective implantation sites were changed between different animals according to the Latin square principle. Ten animals were used. Three materials currently used in mechanical heart valve prostheses-titanium, cobalt-chromium alloy (Haynes 25) and pyrolytic carbon (Pyrolite)--together with a surface modified (methylated) titanium were evaluated. No heparin was given during the experiment. After two hours of testing the discs were explanted and evaluated for hemocompatibility. The thrombus area on each disc was measured with photography and planimetry. Platelet and leukocyte adhesion on the surfaces were quantitatively assessed by scanning electron microscopy (SEM). The results showed that there were significant differences in thrombus formation (p = 0.001) and leukocyte adhesion (p = 0.002) between the materials tested. There was no difference between implantation sites but significant differences between individual animals (p < 0.05).

The results indicate that the method can be used to evaluate early hemocompatibility of biomaterials.