Hemocompatibility of pyrolytic carbon in comparison with other biomaterials

The present generation of mechanical heart-valves prostheses offers significantly improved blood compatibility, combined with appropriate physical and mechanical properties and durability; however, thromboembolism persists as a crucial clinical complication because of the key role played by adsorbed plasma proteins and adherent platelets in determining hemocompatibility. In the present work human plasma protein adsorption and platelet adhesion and activation were evaluated on four materials, selected according to their different physico-chemical and morphological properties: pyrolytic carbon (PyC), titanium alloy Ti–6Al–4V (Ti), tissue culture polystyrene (TCPS) and polystyrene sterilized by γ-irradiation (StPS). Morphological and chemical properties of surfaces were assessed by Time of Flight Secondary Ion Mass Spectrometry (Tof-SIMS), X-ray Photoemission Spectroscopy (XPS), Atomic Force Microscopy (AFM) and Contact Angle (CA) analysis, while protein adsorption and platelet adhesion and activation were evaluated by colorimetric and immunofluorescence tests and Scanning Electron Microscopy (SEM), respectively. Among the analyzed materials, PyC induced the lowest level of protein adsorption and platelet adhesion and activation. In particular, immunofluorescence analysis of fibronectin (FN), fibrinogen (FG), von Willebrand factor (vWF), Hageman factor (FXII) and albumin (ALB) showed that PyC surface was characterized by high levels of FG adsorption, low levels of FN, ALB and vWF and the absence of FXII. Finally, when analyzing the biological response as a function of surface properties, it was found that protein adhesiveness increased with increasing contact angle values. To the contrary, platelet activation related to the total amount of adherent proteins was poor while cell activation was possibly dependent on the detailed composition of the underlying protein layer. Furthermore, differences in surface roughness of the examined materials did not seem to influence the biological response in terms of platelet activation and protein adsorption.

Research highlights
► Protein multilayer found on all biomaterials after whole plasma incubation.
► Pyrolytic carbon adsorbs less proteins and titanium most.
► Fibrinogen adsorbed on pyrolytic carbon do not induce platelet adhesion.
► Greater platelet activation on polystyrenes.
► Good correlation between hydrophilicity and scarcity of proteins/platelets adsorption.