Comparative Study of Anti-Thrombotic Behavior Between Nitrogen-Doped and Nitrogen-Free Hydrogenated Amorphous Carbon Films Fabricated by PIII-D

The usual failure of blood-contacting biomedical materials and devices arises from thrombogenesis and it has prompted researchers to develop new materials and improve the fabrication processes. Amorphous carbon films are being developed to take advantage of their good biocompatibility in blood contacting devices such as rotary blood pumps, artificial heart, mechanical heart valves, and coronary artery stents. Recently, carbon nitride films have received much attention because of their good properties similar to DLC films. In this work, we compare the anti-thrombotic properties between nitrogen-doped and nitrogen-free hydrogenated amorphous carbon (a-C:H:N and a-C:H) films as potential blood-contacting biomedical materials. Nitrogen-doped and nitrogen-free hydrogenated amorphous carbon (a-C:H:N and a-C:H) films were deposited by plasma immersion ion implantation-deposition (PIII-D) using Ar/C₂H₂ and N₂/C₂H₂ gas mixtures, respectively. The deposition was carried out at a constant RF power of 500 W. Surface thrombogenicity of the two films was evaluated by using the in vitro tests. The platelet adhesion test was used to examine the behavior of platelets attached to the film surfaces. The activated partial thromboplastin time (aPTT) test was used to examine the coagulation behavior of the endogenesis clotting system in contact with the film surfaces. The results show that the anti-thrombotic property of the films was improved by nitrogen doping. This improvement was due to the change of the film wettability caused by nitrogen doping. The structure differences between the two films were also investigated using micro-Raman and Fourier transform infrared spectroscopy (FTIR). Incorporation of nitrogen in the films causes the evolution of the D peak in the Raman spectra due to the formation of aromatic rings and inclusion of nitrogen into the sixfold carbon ring structure in a-C:H breaks the symmetry in the sp² domains, which affect the wettability of the film.