A HISTOMORPHOMETRIC COMPARISON OF THE MUSCULAR TISSUE REACTION TO STAINLESS-STEEL, PURE TITANIUM AND TITANIUM-ALLOY IMPLANT MATERIALS

The in vivo tissue reaction to titanium and titanium-based alloys using quantitative histomorphometry was investigated. According to the guidelines for biomaterials testing suggested by ISO, 2 mm x 6 mm cylindrical specimens of chemically pure (CP) Ti, TiO2, electrolytically coated Ti, Ti6Al4V, TiO2-coated Ti6Al4V, TiN physical vapour deposition-coated Ti6Al4V and Ti5Al2.5Fe were implanted in the paravertebral muscles of rats, for 1-52 weeks, 316L stainless steel being used as a control implant material. After PMMA embedding, electrochemical dissolution of the implants, microtome sectioning and Masson's trichrome staining, the tissue reaction was assayed using a semi-automatic method based on the digitization of both the encapsulating membrane contours and the different cell types located within it. All materials induced a close tissue reaction. There was no statistical difference between the tested materials regarding the time-evolution of the inflammatory cells. However, when comparing CP Ti with 316L, a significant difference was found in the fibrocyte kinetics: in the short term, fibrocyte densities were lower for 316L, while beyond 12 weeks, they exhibited higher values than CP Ti. To a lesser extent, a similar observation was made when comparing CP Ti with Ti5Al2.5Fe. No statistical difference was found in the comparison of CP Ti with Ti6Al4V. The membrane thickness was identical for all tested materials and appeared not to be time-dependent.