The synergistic role of hierarchical macro- and mesoporous implant surface and microscopic view of enhanced osseointegration
Abstract: The trend for designing of a titanium implant explored using different chemical compositions and crystallinity materials until people realized that the implant surface character was another important factor affecting the rate and extent of osseointegartion. Titanium received a macroporous titania surface layer by anodization, which contains open pores with average pore diameter around 5?m. An additional mesoporous titania top layer was created that followed the contour of the macropores and having 100–200 nm thickness and a pore diameter of 10 nm. Thus, a coherent laminar titania surface layer was obtained producing a hierarchical macro- and mesoporous surface. The interfacial bonding between the surface layers and the titanium matrix was characterized by a scratch test that confirmed a stable and strong bonding of the laminar titania surface layers upon titanium. The wettability to water and the effects on the osteosarcoma cell line (SaOS-2) proliferation and mineralization of the formed titania surface layers were studied systematically by cell culture and scanning electron microscopy (SEM). A synergistic role of the hierarchical macro- and mesoporosities was revealed in terms of enhancing cell adhesion, proliferation and mineralization, when compared with the titania surface with solo porosity scale topography.For the in vivo results of the evaluation of osseointegration, an argon ion beam polishing technique was applied to prepare the cross sections of implants feasible for the high resolution SEM investigation. The interfacial microstructure between newly formed bone and implants with four modified surfaces including the new hierarchical macro- and mesoporous implant surface retrieved after in vivo tests were characterized. By this approach it has become possible to directly observe early bone formation, the increase of bone density, and the evolution of bone structure. The two bone growth mechanisms, distant osteogenesis and contact osteogenesis, can also be distinguished. These direct observations give, at microscopic level, a better view of osseointegration and explain the functional mechanisms of various implant surfaces for osseointegration.
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