Cell adhesion to nitrogen-doped DLCs fabricated by plasma-based ion implantation and deposition method using toluene gas

Diamond-like carbon (DLC) is a kind of carbon materials and it is considered to have an excellent biocompatibility. DLC coating to the surface of various materials was proposed to improve the biocompatibility of materials. It is possible that DLC is able to apply to biomaterials such as artificial vessel, tooth root and joint in the future. However, the relationship between fine structure, morphology, element doping, etc. in DLCs and the biocompatibility is not clear yet. As a kind of barometer of the biocompatibility, in this study, we have investigated the cell adhesion to nitrogen-doped DLCs fabricated by the PBIID method using toluene gas.The cell adhesion percentage for a non-doped DLC was 75.6%. That for nitrogen-doped DLCs increased monotically from 78.3% to 87.6% with an increasing nitrogen concentration, up to 0.7%. However, when the nitrogen concentration was more than 0.7%, the adhesion percentage saturated at about 87%. As a result, the cell adhesion percentage for nitrogen-doped DLCs was enhanced more than 10% in comparison with that for a non-doped DLC. It is considered that the cell adhesion percentage is improved due to C–N and N–H bonds that promoted the protein adsorption on the surface of the sample, and that the surface became hydrophilic excessively at the nitrogen concentration more than 0.7% and the electrostatic effects were cancelled.