Evaluation of platelet adhesion and activation on materials for an implantable centrifugal blood pump

A totally implantable centrifugal artificial heart has been developed in which a pivot bearing supported centrifugal pump is used as a blood pump. The following have been adopted as blood contacting materials in our pump: titanium alloy (Ti-6Al-4V) for the housing and impeller, alumina ceramic (Al₂O₃) for the male pivots, and ultrahigh molecular weight polyethylene (PE) for the female pivots. Greater antithrombogenicity is required for an implantable blood pump. To examine the thrombogenicity of these materials, we evaluated in vitro platelet adhesion and activation, which may play key roles in thrombogenesis on foreign surfaces. Ti-6Al-4V, Al₂O₃, and PE were compared with polycarbonate (PC), silicone carbide (SiC), and pure titanium (pTi). Platelet adhesion was assessed using monoclonal antibody (CD61) directed against glycoprotein IIIa. Platelet activation was evaluated by measuring P-selectin (GMP-140) released from irreversibly activated platelets. Each material with a surface area of 16.6 cm² was incubated with 2.5 ml of plasma or 2.5 ml of heparinized fresh whole blood for 3 h at 37°C. The optical density (OD) at a wavelength of 450 nm for CD61 was 0.93 ± 0.35 in PC, 0.34 ± 0.13 in PE, 0.27 ± 0.13 in pTi, 0.26 ± 0.01 in Al₂O₃, 0.21 ± 0,04 in SiC, and 0.12 ± 0.12 in Ti-6Al-4V. The GMP-140 levels of the tested materials were not significantly different from the control value (45.9 ± 7.2 ng/ml). These results indicate that Al₂O₃, PE, and Ti-6Al-4V, which are incorporated into our implantable centrifugal pump, have satisfactory antithrombogenic properties in terms of platelet adhesion. However, platelet activation by any material was not observed under the static condition in this study.