Biological and osseointegration capabilities of hierarchically (meso-/micro-/nano-scale) roughened zirconia.
Purpose
Zirconia is a potential alternative to titanium for dental and orthopedic implants. Here we report the biological and bone integration capabilities of a new zirconia surface with distinct morphology at the meso-, micro-, and nano-scales.


Methods
Machine-smooth and roughened zirconia disks were prepared from yttria-stabilized tetragonal zirconia polycrystal (Y-TZP), with rough zirconia created by solid-state laser sculpting. Morphology of the surfaces was analyzed by three-dimensional imaging and profiling. Rat femur-derived bone marrow cells were cultured on zirconia disks. Zirconia implants were placed in rat femurs and the strength of osseointegration was evaluated by biomechanical push-in test.


Results
The rough zirconia surface was characterized by meso-scale (50 µm wide, 6-8 µm deep) grooves, micro-scale (1-10 µm wide, 0.1-3 µm deep) valleys, and nano-scale (10-400 nm wide, 10-300 nm high) nodules, whereas the machined surface was flat and uniform. The average roughness (Ra) of rough zirconia was five times greater than that of machined zirconia. The expression of bone-related genes such as collagen I, osteopontin, osteocalcin, and BMP-2 was 7-25 times upregulated in osteoblasts on rough zirconia at the early stage of culture. The number of attached cells and rate of proliferation were similar between machined and rough zirconia. The strength of osseointegration for rough zirconia was twice that of machined zirconia at weeks two and four of healing, with evidence of mineralized tissue persisting around rough zirconia implants as visualized by electron microscopy and elemental analysis.


Conclusion
This unique meso-/micro-/nano-scale rough zirconia showed a remarkable increase in osseointegration compared to machine-smooth zirconia associated with accelerated differentiation of osteoblasts. Cell attachment and proliferation were not compromised on rough zirconia unlike on rough titanium. This is the first report introducing a rough zirconia surface with distinct hierarchical morphology and providing an effective strategy to improve and develop zirconia implants.
['Rezaei|Naser Mohammadzadeh|NM|', 'Hasegawa|Masakazu|M|', 'Ishijima|Manabu|M|', 'Nakhaei|Kourosh|K|', 'Okubo|Takahisa|T|', 'Taniyama|Takashi|T|', 'Ghassemi|Amirreza|A|', 'Tahsili|Tania|T|', 'Park|Wonhee|W|', 'Hirota|Makoto|M|', 'Ogawa|Takahiro|T|']
D000818:Animals D055396:Bone Morphogenetic Protein 2 D005269:Femur D008297:Male D049329:Nanostructures D016348:Osseointegration D010006:Osteoblasts D015675:Osteocalcin D053495:Osteopontin D019736:Prostheses and Implants D017207:Rats, Sprague-Dawley D013499:Surface Properties D015019:Yttrium D015040:Zirconium
dental and orthopedic implant Y-TZP hierarchical morphology bone–implant integration multi-scale rough