A COMPARATIVE STUDY OF THE BIOACTIVITY OF TITANIUM AND ZIRCONIUM MICROPARTICLES AS A FUNCTION OF TIME

Titanium (Ti) and Zirconium (Zr) are metallic biomaterials employed for biomedical implants. Given that corrosion leads to the release of ions and/or particles to the bio-environment, potential adverse effects must be considered in the choice of metals employed in prosthetic structures. The aim of the present study was to evaluate and compare, as a function of time (0, 3, 6 and 18 months) the distribution, destination and potential risk of Titanium and Zirconium particles that might result from the corrosion process. Male Wistar rats were injected intraperitoneally (i.p.) with a Titanium Dioxide suspension (Group Ti) (1.60g/100g body weight) or Zirconium Dioxide (Group Zr) at equal doses or saline solution (Group C). The following end-points were evaluated at 0, 3, 6 and 18 months: a) the presence of particles in blood cells employing blood smears, b) titanium and zirconium deposits in histological sections of liver and lung, quantitative evaluation of deposits by Atomic Emission Spectroscopy, c) oxidant-antioxidant balance in tissue homogenates by TRAP (Total radical-trapping anti-oxidant parameter analysis), Superoxide Dismutase (SOD) and TBARS (thiobarbituric acid reactive substances), and d) generation of the anion superoxide (O2-) by nitroblue tetrazolium reduction in alveolar macrophages (AM). The presence of Ti and Zr particles was detected in mononuclear phagocytic cells in blood smears and in organ parenchyma. Ti content was higher than Zr at equal doses and times post-administration, in keeping with the histological findings. At all the time-points, Group Ti lungs exhibited a marked reduction in the activity of the antioxidant enzymes SOD and TRAP, whereas liver only revealed SOD consumption. At 3, 6 and 18 months Group Zr showed a reduction only in SOD levels in both organs. The consumption of antioxidant enzymes was always greater in Group Ti compared to Group Zr. In lung, at all the experimental times evaluated, Ti elicited a significant rise in the generation of O2- whereas Zr induced a significant increase compared to control values only at 18 months. It is noteworthy that at earlier times Zr did not alter the redox metabolism in AM and that the increase in this oxidant specie observed at 18 months was significantly smaller than that induced by Ti. The present data suggest that the biocompatibility of Zr is better than that of Ti. Grants: ANPCyT PICT 33493, UBA O-020, CONICET PIP 6042, Fundación Roemmers.