Classification of DLC films in terms of biological response

In this study, various kinds of diamond-like carbon (DLC) films were classified in terms of their biological responses (specifically the number of adhering cells). Forty three kinds of DLC samples that had been deposited on Si substrate by various physical vapor deposition (PVD) and chemical vapor deposition (CVD) system equipment were obtained at random from coating companies, universities, and public organizations in Japan. Mouth fibroblasts (NIH-3T3) were used to estimate the cellular responses on the DLC samples. During the cell culture, 12 of the DLC samples were peeled off from the Si substrates. As a result, the remaining 31 DLC samples with a wide range of properties were classified into four groups in terms of their number of adhering cells. Group 1 (high density, low sp2 content, and low hydrogen contents) and Group 2 (low or medium density, high sp2 content, and low hydrogen contents) had a low number of adhering cells. Group 3 (medium density, and medium sp2 content, and relatively high hydrogen contents) and Group 4 (low sp2 content, low density, and a wide range of hydrogen contents) had a wide range of number of adhering cells. Especially, 7 DLC samples in Group 4 had good cell growth. It was shown that this classification is one of the design criteria of DLC film deposition for biomaterials regardless of the various deposition system equipment. It is expected that ordinary DLC users can carefully select a DLC film for specific applications to medical devices using the classification.