Enhanced osteoblast function on ultraviolet light-treated zirconia

Unlike titanium, surface roughening of zirconia for enhanced bone integration has been technically challenging. The photochemical reaction of semiconductor oxides, e.g., titanium dioxide, has earned considerable and broad interest in environmental and clean energy sciences. This study determined whether ultraviolet (UV) light treatment of zirconia enhances its bioactivity on osteoblasts. Machined zirconia disks were treated with UV light for various time periods up to 48 h. UV light treatment for 48 h increased the rates of attachment, spread, and proliferation of rat bone marrow-derived osteoblasts. Alkaline phosphatase-positive and mineralized nodule areas doubled on UV light-treated zirconia. The expression of osteoblastic genes, such as osteopontin and osteocalcin, was not modulated by UV light treatment. X-ray diffraction and X-ray photoelectron spectroscopy analyses showed that zirconia disks consisted of monoclinic and tetragonal phases of ZrO2 and Y2O3 having a wide light absorption band of 200–400 nm with its peak at <250 nm. UV light treatment transformed the zirconia surface from hydrophobic to hydrophilic status and reduced the atomic percentage of surface carbon in a UV light dose-dependent manner. These results suggest that UV treatment of yttrium-containing partially stabilized zirconia enhances its bioactivity on osteoblasts, in terms of their attachment, proliferation, and eventually mineralization. This biofunctionalization was associated with UV light-catalytic hydrophilic conversion of zirconia surfaces and progressive removal of hydrocarbons.