Ultraviolet Treatment Overcomes Time-Related Degrading Bioactivity of Titanium

The shelf life of titanium implant products, that is, a possible time-related change of their bioactivity, has rarely been addressed. The objective of this study was to examine the bioactivity of newly processed and aged titanium surfaces and determine whether ultraviolet (UV) light treatment of the titanium surface restores the possible adverse effects of titanium aging. Titanium disks, either acid-etched or sandblasted, were used immediately after processing (fresh surface) or after storing in dark for 4 weeks (aged surface). Some disks were treated with UV light for 48 h after 4 weeks of storage. Albumin adsorbed to the aged surfaces was only 15% of that adsorbed to the fresh surfaces during 2-h incubation, whereas UV-treated aged surfaces adsorbed equivalent amount of albumin to that for the fresh surfaces. During 24-h incubation, the number of human mesenchymal stem cells attached to the aged surfaces was less than half of that for the fresh surfaces, whereas UV treatment of the aged surfaces increased the number three times. Proliferation, alkaline phosphatase activity, and calcium deposition of the cells were substantially lower on the aged surfaces than on the fresh surfaces, while those on the UV-treated aged surfaces were higher than on the fresh surfaces. The strength of bone-implant integration evaluated at week 2 of healing in a rat femur model was reduced to half after 4 weeks of titanium aging, whereas UV treatment of the aged implants increased the strength to the level equivalent to or even higher than the freshly prepared implants. Fresh and UV-treated aged surfaces were superhydrophilic, while the aged surface was hydrophobic. The data suggest that bioactivity of titanium surfaces degrades with time and that UV treatment of the aged surface increases the bioactivity over the level of the freshly prepared surface.