Photofunctionalization of Titanium: An Alternative Explanation of Its Chemical-Physical Mechanism

Abstract

Objectives: To demonstrate that titanium implant surfaces as little as 4 weeks from production are contaminated by atmospheric hydrocarbons. This phenomenon, also known as biological ageing can be reversed by UVC irradiation technically known as photofunctionalization. To propose a new model from our experimental evidence to explain how the changes in chemical structure of the surface will affect the adsorption of amino acids on the titanium surface enhancing osteointegration.

Methods: In our study XPS and AES were used to analyze the effects of UVC irradiation (photofunctionalization) in reversing biological ageing of titanium. SEM was used to analyze any possible effects on the topography of the surface.

Results: UVC irradiation was able to reverse biological ageing of titanium by greatly reducing the amount of carbon contamination present on the implant surface by up to 4 times, while the topography of the surface was not affected. UVC photon energy reduces surface H2O and increases TiOH with many -OH groups being produced. These groups explain the super-hydrophilic effect from photofunctionalization when these groups come into contact with water.

Significance: Photofunctionalization has proven to be a valid method to reduce the amount of hydrocarbon contamination on titanium dental implants and improve biological results. The chemisorption mechanisms of amino acids, in our study, are dictated by the chemical structure and electric state present on the surface, but only in the presence of an also favourable geometrical composition at the atomical level.

Fig 1

A) The XPS survey spectra obtained for the BASE(red) and RAPID (blue) implants as received. On both surfaces Ti, O, C, Al and F were detectable. B) High resolution XPS spectrum of the Ti2p core line for RAPID implant. The shape of the 2p doublet was fitted by to five sub-doublets. The doublet with the highest intensity corresponded to TiO₂ component. The enlarged region presented the Ti2p_3/2 peaks corresponded to hydrated water Ti-OH, various oxidation states and metallic state of titanium.

Fig 2. Electron microscope images obtained from magnification x500 recorded for BASE (a) and RAPID (b) implants as received.

The contrast from light to dark areas suggest a considerable degree of roughness of the analysed areas. Comparing (a and b) the surfaces of both type implants are quite similar.

Fig 3. The chemical distribution maps of oxygen (a), carbon (b) and titanium (c) obtained for the RAPID implant.

The distribution of the elements is grain type with carbon spread all over the surface while titanium is almost homogenous.

Fig 4. The C1s (a) and O1s (b) core lines recorded for as received and after photofunctionalization samples.

The lines in red show the decontamination effect of the UVC irradiation decreasing the hydrocarbons peak and increasing the Oxygen peak.

Fig 5. Line shape analysis of C1s and O1s spectra for the implant as received (a and c) and after photofunctionalization (b and d).

Comparing (a and b) the intensity of the peak at 285 eV corresponding to the carbon contamination is highly reduced. The oxygen lines (c and d) show an increase in oxygen peak.

Fig 6. Scheme representing the interactions of carboxyl and amine groups with TiO2 surface when exposed to the atmosphere.

The surface shown is TiO2 (110), with Ti (light blue) and O (orange). See text for details.