In vitro vs. ex vivo platelet deposition on polymer surfaces

The initial adherence and activation of platelets on a surface may be a major determinant of the thrombogenicity of that surface. The response of platelets to four polymers: polyethylene (PE), polyvinyl chloride (PVC), silicone rubber (SIL), and oxidized polyethylene (OX-PE) was studied in vitro with scanning electron microscopy. Platelets from mongrel canines and rhesus monkeys were obtained just prior to cannulation of the donor animal with an ex vivo arteriovenous series shunt evaluating the same four polymers. Thus, the in vivo response of circulating platelets could be compared to the in vitro response of purified platelets from the same animal. In the canine the in vitro response of individual platelets deposited on the four polymers studied was nearly the same as the ex vivo response although the extent of shape-change was usually somewhat greater ex vivo. Large numbers of fully spread platelets were seen on OX-PE and fewer numbers on PE both in vitro and ex vivo. Mixtures of platelets in all degrees of shape-change/activation wer characteristic on PVC, while platelets on SIL showed little shape-change over all time intervals. Rhesus platelet response was similar to the canines' except that fewer attached or shape-changed, and differences in responses to the four polymers were less pronounced. The similarity of the in vitro to the ex vivo response in each of the species suggests that this simple in vitro model can be informative in studying platelet shape-change/activation as a precursor to surface induced thrombosis with less complexity and expense than in vivo methods.