Correlation Between Optical Constants and Cell Adhesion on Diamond-Like Carbon Films

Although diamond -like carbon (DLC) films have a wide range of potential applications, the lack of objective assessment indices has limited the manufacturing and applicability of DLC films. In this study, we deposited four types of DLC films -a-C, graphite film, a-C:H, and polymer -like -onto a cover glass as per ISO 23216:2021 and assessed the adhesion of NIH-3T3 cells onto their surfaces. The optical constants (refractive indices and extinction coefficients) were measured via spectroscopic ellipsometry. The relative hydrogen content was examined via glow discharge optical emission spectrometry (GD-OES), while the surface properties were assessed via X-ray photoelectron spectroscopy (XPS). a-C:H and polymer -like DLC films, on which the formation of cell aggregates was observed, had relatively low extinction coefficients and higher hydrogen content than other DLC films; moreover, the formation of oxygen -containing functional groups on the surfaces of a-C:H and polymer -like DLC films was minimal. The extinction coefficients of the DLC films comprehensively reflected the basic structures and surface characteristics of the DLC films, thus indicating that extinction coefficients could potentially act as an index of cell aggregation.