On the research only original surface of the PBS immersed sample, the two ionic contributions are fitted with one broad structure. After 60 sec of sputtering all structure related to the surface modification is removed and only the contribution from the bulk remains. The outermost part of the oxidized layer on the bovine lubricated surfaces is terminated by a Cr hydroxide. After 30 sec of sputtering the hydroxide decreases in intensity and the surface is now terminated by Cr3+ oxide with trace of hydroxide still left. C 1s spectra from the bovine lubricated surfaces are displayed in Figure 5B. Spectra from the outermost surface obtained in and outside the wear track are decomposed into four and three peaks, respectively. The main peak at 284.5 (C1) can be associated to C�CC and C�CH bonds, the C2 peak shifted 1.

5 eV is associated to C�CO bonds, and the C3 component shifted 3.7 eV to N-C = O bonds.22,23 These structures are observed in the spectrum recorded in and outside the wear track of the original surfaces and after sputtering for 30 sec in the wear track. The C4 component shifted 6.4 eV relative to the main line is only observed in the spectrum from the wear track and is assigned to O = C-O bonds.24 The C4 structure shows that the normal peptide bonds have been partly oxidized in the wear track. Figure 5C shows the N 1s spectra from the bovine lubricated CoCr surface. The main peak is situated at 399.9 eV. The peak on the high energy side shifted 2.5 eV to higher energies is only observed in the spectra from the wear track. Si 2p spectra from Si3N4 samples lubricated with PBS solution and bovine serum are shown in Figure 6A.

All spectra were recorded in un-sputtered condition and have similar appearance with one bulk related component (SiB) at 101.3 eV and one surface related component SiS shifted 1.3 eV. The SiS component is associated with SiO2/SiOx-OHy. The binding energy value for the SiB component is lower than the values reported in the literature (102 eV25,26) while the energy shift to the oxide component is in line with earlier reported values for the SiO2/SiOx-OHy.26,27 Figure 6. XPS spectra obtained from bovine and PBS lubricated Si3N4 surfaces; (a) Si2p peak; (b) N 1s peak; (c); C 1s peak. The N 1s spectra are recorded from the wear track on samples that have been lubricated with either PBS solution or bovine serum, Figure 6.

In the case of PBS solution the spectrum can be fitted with one component and in the case of bovine serum the spectrum is composed of two distinct components. GSK-3 During sputtering of the bovine lubricated surface the N2 component diminish after around 60 sec (not shown). The N1 component at a binding energy of 397 eV is associated to the bulk material and the N2 component shifted 2.6 eV to the peptide containing tribosurface. Also here the binding energy of the bulk component is somewhat lower than the values reported in the literature.