Scientists from the Tokyo Medical and Dental University (TMDU) 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 new generation medical implants that last longer.