Platelet adhesion on hard material coatings and bonding agents for ventricular assist devices in a flow chamber

Rotary blood pumps (RBPs), used as Ventricular assist devices (VADs), feature a suspended impeller (rotor) within a housing (stator). Titanium alloys are mostly used for those parts, but their limited wear resistance in critical contact areas, leading to scratches and promoting thrombus formation. Therefore, hard material coatings (HMCs) can be applied to increase wear resistance and bonding agents ensure stable coatings on the bulk material. Still, coating damage may occur and expose the material to blood, requiring hemocompatibility assessment. Therefore, their hemocompatibility must be evaluated as well as that of the HMCs. Platelet adhesion as thrombus formation indicator was investigated using an in vitro flow chamber and fluorescence microscopy for the following materials: Silicon diamond-like carbon (SiDLC), titanium nitride with and without droplets (TiN_D, TiN), bonding agents chrome (Cr), chrome nitride (CrN), uncoated Ti6Al4V (Ti), and aluminum (Alu) as positive control. CFD simulations determined wall shear rates, averaging 5730.5 1/s on the evaluated area. The normalized percentage of the covered surface (NCSA) area was statistically evaluated (p-values, Wilcoxon effect size). NCSA analysis showed that Alu had the highest value (8.7), significantly exceeding CrN and SiDLC (both 0.3, p < 0.05). Cr (3.6) exhibited significantly more platelets than CrN with a medium effect compared to CrN, Ti (0.2), TiN (0.3), and SiDLC, and a weak effect compared to TiN_D (0.4) and Alu. No significant differences were observed among HMCs, Ti, and CrN. This study highlights Cr's elevated thrombogenicity, whereas the other surfaces (except Alu) showed hemocompatibility comparable to Ti, supporting their use in VADs.