The Electrochemical Behavior of Ti in Human Synovial Fluids

Abstract

In this study, we report results of the interaction of titanium (Ti) with human synovial fluids. A wide palette of electrochemical techniques was used, including open circuit potential, potentiodynamic methods, and electrochemical impedance. After the electrochemical testing, selected surfaces were analyzed using Auger Electron Spectroscopy to provide laterally resolved information on surface chemistry. For comparison purposes, similar tests were conducted in a series of simulated body fluids. This study shows that compared to the tested simulated body fluids, synovial liquids show a large patient variability up to one order of magnitude for some crucial electrochemical parameters such as corrosion current density. The electrochemical behavior of Ti exposed to human synovial fluids seems to be controlled by the interaction with organic molecules rather than with reactive oxygen species.

Keywords: Ti; electrochemistry; human synovial fluid.

Figure 1

(a) Schematic diagram of the three-electrode cell. A: working electrode, B: counter electrode, C: reference electrode, D: air evacuation hole, E: sealing O-ring, F: tested synovial fluid, G: vessel, H: injection hole, I: vessel cover. (b) The picture of the cell.

Figure 2

Experimental sequence.

Figure 3

Pictures of human synovial fluids inside the syringe before electrochemical measurements.

Figure 4

(a) Evolution of OCP with immersion time in the synovia from P2–4 and (b) stabilized OCP results of Ti after 20 minutes’ immersion in different synovial fluids from PS, TKA (P17), and R (P6) group.

Figure 5

(a) Rp measurement of Ti for P6 and (b) comparison of Rp value of Ti in all synovial fluids.

Figure 6

(a) Bode plot of Ti in synovia from P3 and (b) Rs of synovial fluids from different patients (initial: before potentiodynamic polarization, final: after all measurements completed).

Figure 7

Cathodic polarization curves (logarithmic scale of the absolute current density) of Ti tested in synovial fluids from PS, TKA (P17) and R (P6) group.

Figure 8

Anodic polarization curves (logarithmic scale of the absolute current density) of Ti tested in synovial fluids from PS, TKA (P17 with two repetitions), and R (P6) group.

Figure 9

AES analysis of Ti surfaces exposed at OCP to synovial fluid from patient 4 and 5. (a–c) are for P4; (d–f) are for P5; (a,d): secondary electron images and analyzed points; (b,e): depth profile on analysis point 1; (c,f): depth profile on analysis point 3; Differential intensity is plotted in the depth profile.

Figure 10

(a) Cathodic and (b) anodic polarization curves (logarithmic scale of the absolute current density) of Ti in simulated body fluid solutions.

Figure 11

Anodic polarization curves of Ti tested in simulated fluids and in synovial fluids.

Figure 12

Rp measurements of Ti tested in simulated fluids and in synovial fluids with a scan rate of 2 mV/s and 0.6 mV/s.