FRETTING FATIGUE PROPERTIES OF TI-6AL-4V ALLOY IN PSEUDO-BODY FLUID AND EVALUATION OF BIOCOMPATIBILITY BY CELL-CULTURE METHOD

Plain and fretting fatigue tests of an annealed Ti-6A1-4V alloy were c arried out in ca. 150 mt of a pseudo-body fluid. A. phosphate-buffered saline without calcium and magnesium salts (PBS(-)) was used as a pse udo-body fluid, and nitrogen gas was bubbled into the saline during th e tests in order to reduce the concentration of dissolved oxygen in th e saline. The fretting fatigue strength in PBS(-) was lower than those in the air at higher and lower stress amplitudes ranges, while the fa tigue strengths in both environments were almost equivalent to each ot her. Released metallic ions and debris in PBS(-) recovered after frett ing fatigue tests under condition A (the stress amplitude, sigma(a) is set at 250 MPa) and B (sigma(a) is set at 131 MPa) were quantitativel y analyzed by graphite furnace atomic absorption spectrophotometry (GF AAS). Before the analysis, some volume of the recovered PBS(-) were fi ltered through a 0.22 mu m pore size filter. The unfiltered fluid of c ondition A contained iron, manganese, nickel, vanadium, chromium, alum inum and titanium in 42, 110, 110, 130, 970, 1150 and 2420 ppb (mu g/L ), respectively. Nickel, iron, aluminum and manganese in 24, 4, 3 and 2 ppb, respectively, were found in the filtered fluid of condition B, suggesting that corrosion by passive-active cell occurred between the fresh surface of crack-tips or fretting area and other surface covered by oxide films during the fretting fatigue test. Cytotoxicity of the fluids of conditions A and B was investigated using MC3T3-El cells. Bo th of the filtered and the unfiltered fluids of the condition B were t oxic for the cells, but only the unfiltered fluid of the condition A w ere toxic for the cells. These facts suggest that metallic substances in small concentrations as 10 ppb have cytotoxicity, and that not mere ly the amount but also the state of metallic elements affect the exten t of cytotoxicity of the fluids.