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The objectives of this study are to evaluate long-term wettability of novel surface-engineered, clinically available dental implants, featuring a surface nanolayer of covalently linked hyaluronan, and to confirm the relationships between wetting properties and surface nanostructure and microstructure. Wettability measurements were performed on clinically available hyaluronan-coated Grade 4 titanium implants, packaged and sterile, that is, in the "on the shelf" condition, after 1 year from production. Wetting properties were measured by the Wilhelmy plate method. Analysis of the surface structure and chemistry was perfomed by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) analysis, atomic force microscopy (AFM), and ζ -potential measurement, either on implants or disks or plates subjected to the same surface-engineering process. Results show that hydrophilicity and ensuing capillary rise of the hyaluronan-coated implant surface is unaffected by aging and dry storage. Chemical analysis of the implant surface by XPS and evaluation of the ζ potential indicate that hyaluronan chemistry and not that of titanium dictates interfacial properties. Comparison between XPS versus EDX and SEM versus AFM data confirm that the thickness of the hyaluronan surface layer is within the nanometer range. Data show that nanoengineering of the implant surface by linking of the hydrophilic hyaluronan molecule endows tested titanium implants by permanent wettability, without need of wet storage as presently performed to keep long-term hydrophilic implant surfaces. From an analytical point of view, the introduction in routine clinical practice of nanoengineered implant surfaces requires upgrading of analytical methods to the nanoscale.

The goal of this study was the in vivo evaluation of nanoporous titanium (Ti) implants bearing a covalently linked surface hyaluronan (HA) layer. Implant surface topography and surface chemistry were previously evaluated by scanning electron microscopy and X-ray photoelectron spectroscopy. Results showed that the surface modification process did not affect surface topography, yielding a homogeneously HA-coated nanotextured implant surface. In vivo evaluation of implants in both cortical and trabecular bone of rabbit femurs showed a significant improvement of both bone-to-implant contact and bone ingrowth at HA-bearing implant interfaces at 4 weeks. The improvement in osteointegration rate was particularly evident in the marrow-rich trabecular bone (bone-to-implant contact: control 22.5%; HA-coated 69.0%, p < 0.01). Mechanical testing (push-out test) and evaluation of interfacial bone microhardness confirmed a faster bone maturation around HA-coated implants (Bone Maturation Index: control 79.1%; HA-coated 90.6%, p < 0.05). Suggestions based on the biochemical role of HA are presented to account for the observed behavior.