Biotribocorrosion of titanium implants: chronic effect of micro and nanoparticles.

Titanium biomedical implants remain in place in the patient’s body over extended periods of time, and it is therefore of interest to evaluate the tissue effects of titanium dioxide (TiO2) micro- (MPs) and nano-particles (NPs) that result from biotribocorrosion, at long-term experimental time points. OBJECTIVE: To evaluate biological response to titanium MPs and NPs in plasma, liver, lung, and kidney at 6 months. METHODS: Wistar rats (n=18) were intraperitoneally injected with a TiO2 suspension (0.16g/100g in 5ml of saline solution): Group NP5 (5nm), Group MP45 (45µm), and Control Group (vehicle). The organs were analyzed histologically. Titanium concentration (TiC) was determined in organs and plasma using spectrometry (ICP-MS). Functional capacity of the liver (ALT, AST, cholinesterase) and kidney (urea, creatinine) was evaluated. Superoxide anion (O2-) generation was assessed in lung alveolar macrophages using NBT (nitroblue tetrazolium). RESULTS: Histologic examination showed the presence of particle deposits in liver, lung, and kidney parenchyma in both experimental groups, with no associated structural alterations. Liver, lung, and plasma TiC was significantly higher in both experimental groups compared to control (p<0.05). In the lung, TiC was significantly higher in MP45 than in NP5 (p<0.05). In the kidney, TiC was significantly higher in the NP5 group than in the MP45 and control groups (p<0.05). Biochemical parameters showed that liver and kidney function remained unaffected. Staining with NBT showed that the percentage of reactive cells was significantly higher in NP5 than in MP45, and was higher in both experimental groups than in the control group (NP5:?:37.51±3.26%; MP45:?:19.24±3.33%; Control:?:7.89±3.4%; p<0.05). CONCLUSION: Although TiC was highest in the liver, and NPs showed highest biopersistence in the kidney, no functional damage was observed. Even though concentration of NPs was significantly lower than that of MPs in the lung, O2- generation by NPs was significantly higher, indicating greater reactivity. The obtained results suggest that biological response to chronic exposure to titanium particles depends not only on average particle size but also on the target organ where the particles deposit.