Assessment and comparison of surface chemical composition and oxide layer modification upon two different activation methods on a cocrmo alloy.

This study investigated the effect of two different activation methods on the surface chemical composition of a CoCrMo-alloy. The activation was performed with oxygen plasma (OP) or nitric acid (NA). The surface physical-chemical properties were thoroughly characterized by means of several analytical techniques: X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), zinc-complex substitution technique, contact angle, and interferometry. The surface modification was evaluated by assessing contamination removal, the "active" hydroxyl groups (OH-act) present at the surface, the metal oxide ratio (CoyO x (-) /CryO x (-) ) and changes in the chemical composition and topography of the oxide layer. XPS experimental data showed for both methods (OP and NA) a significant decrease of the carbon contents (C 1s) associated with contaminants and at the same time changes in the atomic composition of the oxide layer (O 1s). In addition, the O 1s XPS spectra showed differences between the percentage of OH(-) before and after OP or NA treatment, leading to the conclusion that both methods are effective for surface "cleaning" and activation. These results were further investigated and corroborated by ToF-SIMS analysis and zinc complex substitution technique. The general conclusion was that NA is more efficient in terms of contaminants removal and generation of accessible OH-act present at the surface and without altering the native metal oxide ratio (CoyO x (-) /CryO x (-) ) considered to be essential for biocompatibility.