Protein arrangement on modified diamond-like carbon surfaces – An ARXPS study

•DLC coatings were modified by Ar+ ion sputtering and laser graphitisation.•The surface properties of the coatings were measured, and it was found that the above methods increased sp2 content and altered surface energy.•ARXPS was used to observe protein arrangement on the surface.•Polar CO/CN groups were seen to be segregated towards the interface, indicating they play an important role in bonding.•This segregation increased with increasing polar surface energy, indicating an increased net attraction between polar groups. Understanding the nature of the interface between a biomaterial implant and the biological fluid is an essential step towards creating improved implant materials. This study examined a diamond-like carbon coating biomaterial, the surface energy of which was modified by Ar+ ion sputtering and laser graphitisation. The arrangement of proteins was analysed by angle resolved X-ray photoelectron spectroscopy, and the effects of the polar component of surface energy on this arrangement were observed. It was seen that polar groups (such as CN, CO) are more attracted to the coating surface due to the stronger polar interactions. This results in a segregation of these groups to the DLC–protein interface; at increasing takeoff angle (further from to DLC–protein interface) fewer of these polar groups are seen. Correspondingly, groups that interact mainly by dispersive forces (CC, CH) were found to increase in intensity as takeoff angle increased, indicating they are segregated away from the DLC–protein interface. The magnitude of the segregation was seen to increase with increasing polar surface energy, this was attributed to an increased net attraction between the solid surface and polar groups at higher polar surface energy (γSp).