Summary
Titanium has superior osteointegrating properties compared to other biomaterials.
The mechanism for this is unknown. During the initial phase of bone implantation the
biomaterial comes into direct contact with whole blood. In this study we use a newly
developed in vitro chamber model to compare different commonly used biomaterials in
contact with whole blood. These materials were selected with respect to their different
osteointegrating properties in order to correlate these properties with the response
to whole blood. In the presence of 3 IU/ml of heparin only titanium induced macroscopic
clotting. This was reflected by the generation of thrombin-antithrombin which was
much increased in blood in contact with titanium compared with steel and PVC. The
coagulation activation caused by titanium was triggered by the intrinsic pathway because
the generation of FXIIa-AT/C1 esterase inhibitor paralleled that of thrombin-antithrombin,
and both thrombinantithrombin complex and FXIIa-AT/C1 esterase inhibitor generation
were abrogated by corn trypsin inhibitor, which is a specific inhibitor of FXIIa.
The binding of platelets was increased on the titanium surface compared to the other
biomaterial surfaces and the state of platelet activation was much more pronounced
as reflected by the levels of β-thromboglobulin and PDGF. This study indicates that
titanium is unsuitable as a biomaterial in devices which are in direct contact with
blood for a prolonged period. Furthermore, PDGF and other α-granule proteins e.g.
TGF-β, are known to be potent promotors of osteogenesis which suggests that the pronounced
thrombogenic properties of titanium might contribute to the good osteointegrating
properties.
