Effect of the coexistence of albumin and H2O2 on the corrosion of biomedical cobalt alloys in physiological saline

Abstract

The corrosion of Co-28Cr-6Mo and Co-35Ni-20Cr-10Mo, as biomedical alloys, has been investigated for effects of typical species (albumin and H₂O₂) in physiological saline, with their coexistence explored for the first time. Electrochemical and long term immersion tests were carried out. It was found that Co alloys were not sensitive to the presence of albumin alone, which slightly promoted anodic dissolution of Co-35Ni-20Cr-10Mo without noticeably affecting Co-28Cr-6Mo and facilitated oxide film dissolution on both alloys. H₂O₂ led to a clear drop in corrosion resistance, favouring metal release and surface oxide formation and inducing much thicker but less compact oxide films for both alloys. The coexistence of both species resulted in the worst corrosion resistance and most metal release, while the amount and composition of surface oxide remained at a similar level as in the absence of both. The effect of H₂O₂ inducing low compactness of surface oxides should prevail on deciding the poor corrosion protection ability of passive film, while albumin simultaneously promoted dissolution or inhibited formation of oxides due to H₂O₂. Corrosion resistance was consistently lower for Co-35Ni-20Cr-10Mo under each condition, the only alloy where the synergistic effect of both species was clearly demonstrated. This work suggests that the complexity of the environment must be considered for corrosion resistance evaluation of biomedical alloys.

Fig. 1. Electrochemical test results of Co alloys in PS, PS + albumin, PS + H₂O₂ and PS + albumin + H₂O₂ at 37 °C, including 1 h OCP measurements (a and d), anodic polarisation curves (b and d) and cathodic polarisation curves (c and f); a–c are for Co–28Cr–6Mo and d–f are for Co–35Ni–20Cr–10Mo.

Fig. 2. Comparison of anodic polarisation curves of Co–28Cr–6Mo and Co–35Ni–20Cr–10Mo in (a) PS, (b) PS + albumin, (c) PS + H₂O₂ and (d) PS + albumin + H₂O₂.

Fig. 3. Comparison of cathodic polarisation curves of Co–28Cr–6Mo and Co–35Ni–20Cr–10Mo in (a) PS, (b) PS + albumin, (c) PS + H₂O₂ and (d) PS + albumin + H₂O₂.

Fig. 4. Nyquist plots and Bode plots of Co–28Cr–6Mo (a and b) and Co–35Ni–20Cr–10Mo (c and d) in PS, PS + albumin, PS + H₂O₂ and PS + albumin + H₂O₂ at 37 °C obtained after 1 hour open circuit immersion.

Fig. 5. Equivalent circuit applied to fit the EIS plots in Fig. 4.

Fig. 6. Metal release concentrations of (a) Co–28Cr–6Mo and (b) Co–35Ni–20Cr–10Mo after 4 months immersion in PS, PS + albumin, PS + H₂O₂ and PS + albumin + H₂O₂ at 37 °C.

Fig. 7. XPS peaks of (a) O1s and (b) C1s obtained from the surface of Co–28Cr–6Mo alloy in PS and (c) O1S and (d) C1s obtained from the surface of Co–35Ni–20Cr–10Mo alloy in PS after 4 months immersion at 37 °C.

Fig. 8. XPS peaks of Co2p on the surface of (a) Co–28Cr–6Mo and (b) Co–35Ni–20Cr–10Mo after 4 months immersion in PS, PS + albumin, PS + H2O2 and PS + albumin + H₂O₂ at 37 °C.

Fig. 9. XPS peaks of Cr2p on the surface of (a) Co–28Cr–6Mo and (b) Co–35Ni–20Cr–10Mo after 4 months immersion in PS, PS + albumin, PS + H₂O₂ and PS + albumin + H₂O₂ at 37 °C.

Fig. 10. XPS peaks of Mo3d on the surface of (a) Co–28Cr–6Mo and (b) Co–35Ni–20Cr–10Mo after 4 months immersion in PS, PS + albumin, PS + H₂O₂ and PS + albumin + H₂O₂ at 37 °C.

Fig. 11. XPS peaks of Ni2p on the surface of Co–35Ni–20Cr–10Mo after 4 months immersion in PS, PS + albumin, PS + H₂O₂ and PS + albumin + H₂O₂ at 37 °C.

Fig. 12. AFM images of the surface of Co–28Cr–6Mo discs in (a) PS, (b) PS + albumin, (c) PS + H₂O₂ and (d) PS + albumin + H₂O₂ and Co–35Ni–20Cr–10Mo in (e) PS, (f) PS + albumin, (g) PS + H₂O₂ and (h) PS + albumin + H₂O₂ after 4 months immersion at 37 °C.