Morphological changes occurring during thrombogenesis and embolization on biomaterials in a canine ex-vivo series...

An acute canine ex-vivo femoral A-V shunt technique was used to study thrombus formation and embolization on a number of porous and non-porous polymer surfaces over a one-hour blood contact period. The technique allows for simultaneous exposure of all the surfaces under similar physiological and hematological conditions. This makes comparisons between surfaces more reliable. SEM was used to study changes in the morphology of platelets and thrombi present on the polymer surfaces. Quantitative information was obtained using radiolabeled platelets. In general, platelet deposition, activation, and aggregation was followed by thrombus formation which peaked at about 15-30 minutes of blood contact. Thrombi were composed mainly of platelets with few leukocytes present. Embolization was observed on Silastic (SIL), polyvinylchoride (PVC), polyethylene (PE), and oxidized polyethylene (OX-PE) surfaces between 20 and 60 minutes of blood contact. The mechanism for embolization involved clot retraction under the influence of a shear field. Leukocytes did not appear to be necessary for the initiation of embolization but were present during the embolization phase on OX-PE, possibly due to chemotactic factors. Although extensive thrombus formation was observed on the porous PTFE materials (GORE-TEX and IMPRA), the thrombi formed were flat and did not significantly block the lumen. By 60 minutes of blood contact, only minimal embolization had occurred on the PTFE surfaces. SEM examination of the sequence of thrombus formation and embolization was found to correlate well with trends in platelet deposition measured using radiolabeling techniques.