Thin film composites of nanocrystalline ZrO2 and diamond-like carbon: Synthesis, structural properties and bone cell proliferation

We report on the synthesis of thin composites of diamond-like carbon (DLC) and nanocrystalline ZrO2 deposited using pulsed direct current plasma-enhanced chemical vapor deposition at low temperatures (<120 °C). Films containing up to 21 at.% Zr were prepared (hydrogen was not included in the calculation) and their structural and surface properties were determined using a number of spectroscopic methods and contact angle measurements. Bone cell adhesion to the films was studied using a 3 day cell culture with osteoblasts. These nanocomposites (DLC–ZrO2) consist of tetragonal ZrO2 nanocrystals with an average size of 2–5 nm embedded in an amorphous matrix consisting predominantly of DLC. The surface water contact angle of the films increased from ∼60° to 80° as the Zr content increased from 0 to 21 at.%. The cell culture study revealed that although the cell counts were not significantly different, the morphology of the osteoblasts growing on the DLC–ZrO2 nanocomposites was markedly different from that of cells growing on DLC alone. Cells growing on the DLC–ZrO2 surfaces were less spread out and had a smaller cell area in comparison with those growing on DLC surfaces. In some areas on the DLC–ZrO2 surfaces, large numbers of cells appeared to coalesce. It is postulated that the difference in cell morphology between osteoblasts on DLC–ZrO2 surfaces and DLC surfaces is related to the presence of very small tetragonal nanocrystals of ZrO2 in the composite film.