Material-specific thrombin generation following contact between metal surfaces and whole blood

Little is known about the blood compatibility of metals used in various medical devices. We have previously shown that titanium and derivatives thereof are among the most thrombogenic materials which may explain its outstanding osteointegrating properties. The aim of the present study was to characterize the thrombogenic and complement-activating properties of various metals used today in medical applications. Polyester chips were coated with 50- to 100-nm thick layers of aluminium, iridium, indium, nickel, tantalum, tin, titanium, or zirconium using magnetron sputtering. The metal-coated chips were then incubated in direct contact with whole blood in an in vitro chamber model, and the blood was then analyzed for platelet counts, thrombin-antithrombin (AT), fXIIa-AT, fXIa-AT and fXIIa-C1INH complexes and the complement parameters C3a and sC5b-9. Titanium, tantalum and indium were found to exhibit pronounced thrombogenic properties, whereas aluminium, nickel and, in particular, iridium were essentially non-thrombogenic. Tin and zirconium were intermediate activators. All metals activated complement to a similar degree, with the exception of aluminium, which had more pronounced activating properties. This study clearly indicates that metals indeed have varying thrombogenic and complement activating properties. These studies have implications for the selection of metals intended for medical applications.