Band gap energies of the passive film on Ti are relatively small that is one factor generating the excellent biocompatibility. (Credit: Tokyo Medical and Dental University)

Scientists used photoelectrochemical measurement and x-ray photoelectron spectroscopy to clarify the source of titanium’s biocompatibility when implanted into the body, as with hip replacements and dental implants. They find that its reactivity with the correct ions in the extracellular fluid allows the body to recognize it. This work may lead to a new generation of medical implants that last longer.

The researchers tested thin disks of titanium in a solution containing ions meant to mimic the extracellular fluid of the body, as well as in saline. They measured how much photoelectrical current was generated when light of various wavelengths was illuminated on the disks. They also performed x-ray photoelectron spectroscopy to characterize the passive films that were naturally present on the surface of the titanium.

Passive films consisted of a very thin TiO2 layer containing small amounts of Ti2O3 and TiO, hydroxyl groups, and water. The reactivity of titanium with high corrosion resistance, as revealed in this experiment by its electronic band structure, is one of the primary reasons for its excellent biocompatibility among metals. This research may lead to safer and less-expensive implants for hip replacements or dental implants, because titanium is relatively rare and expensive.

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