  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.
