Imparting biocompatibility to zirconia implants with nanosecond pulsed laser: Formation of microgrooves and investigation of heat effects

The purposes of this study were to evaluate the microstructures and chemical composition changes of the surface of tetragonal zirconia polycrystal ( TZP) after irradiation of nanosecond pulsed laser and to consider the effects for biocompatibility. Two types of zirconia ceramics, yttria-stabilized TZP ( Y-TZP) and ceria-stabilized TZP/alumina nanocomposite ( Ce-TZP), were irradiated. To evaluate microstructures, the irradiated samples were observed with a scanning electron microscope ( SEM). Laser irradiation blackened the surface of Ce-TZP; contrastingly, it gave no color change on that of Y-TZP. To identify the chemical composition changes, the samples were characterized using X-ray diffraction XRD), energy dispersive X-ray spectrometry ( EDX) and X-ray photoelectron spectroscopy ( XPS). To examine the changes in the surface chargeability of zirconia, zeta potential was determined. SEM images showed microgrooves, whose widths were the same as that of laser spot ( 30 μm), were formed on the surfaces of both samples, and the surfaces of the grooves were roughened by coagulation materials of a few micrometers in size. Such cell-sized grooves with rough surfaces are considered a favorable environment to help osteoblast cells to grow. XRD patterns showed that laser irradiation induced monoclinic-to-tetragonal phase transform. Because the monoclinic phase was induced by machining or polishing, this result means laser irradiation returned the crystal phase to the bulk state. However, XRD patterns did not reveal the reason of the color change. EDX result showed oxygen atoms decreased on the irradiated surface of both samples. In addition, XPS spectra of Zr3d from Ce-TZP showed a part of Zr4+ shifted to lower side after irradiation. Considering these points, the color change was caused by the generation of oxygen-defficient zirconia. After laser irradiation, zeta potential of Ce-TZP was decreased. This result suggests the possibility that the amount of deposition of ions and proteins in body liquid is decreased. It is concluded that the grooves to improve biocompatibility can be formed on TZP surfaces by nanosecond pulsed laser, but adverse chemical composition change can be occurred by defficiency of oxygen. Additional process may be needed to prevent the phenomenon. 2018 The Japan Institute of Metals and Materials.