ADHESION AND ACTIVATION OF PLATELETS AND POLYMORPHONUCLEAR GRANULOCYTE CELLS AT TIO2 SURFACES

The initial reactions of two TiO2 surfaces with blood were investigate d by short-time exposure to capillary blood and analysis of surface-ad sorbed plasma proteins and surface-adhering cells by using immunofluor escence techniques. Antibodies directed against platelet membrane anti gen and P-selectin were used to visualize platelet adhesion and activa tion. Acridine orange and anti-CD11b were used to detect adhesion and activation of polymorphonuclear granulocytes (PMNs). Antibodies agains t thrombospondin were used as markers for platelet alpha-granules. The fluorescence intensity was quantitated by computer-aided image analys is. Commercially pure, polished sheet titanium was oxidized in two dif ferent ways: (1) the natural oxide was dissolved with hydrofluoric aci d and a new oxide layer was grown by oxidation in nitric acid, or (2) annealing was performed at 700 degrees C in air. Auger electron spectr oscopy and x-ray photoelectron spectroscopy showed that both surfaces had similar composition consisting of TiO2 covered by a carbonaceous s urface contamination layer. The thickness of the oxide layer was 4 nm on the acid-oxidized surface and 39 nm on the annealed surface. Optica l profilometry and scanning electron microscopy showed that the acid-o xidized surface was rough and the annealed surface was smooth. The fib rinogen/prothrombin-thrombin ratio in the initial protein film differe d between the surfaces. The number of adhering platelets was larger at the surface with a high surface concentration of adsorbed fibrinogen. Platelet activation (CD62) and priming of PMNs (CD 11b) were also sig nificantly higher on the acid-oxidized surface. The results indicate t hat non-self recognition of biomaterials is an array of transient reac tions comprising protein-material, protein-cell, and cell-cell interac tions.