Multifunctional surfaces for implants in bone contact applications

The idea behind this thesis is the use of natural molecules to confer to the surface of biomaterials for bone contact applications multifunctional properties by means of functionalization. Natural molecules can be extracted from plants or food waste and wine industries, in order to obtain molecules with high added value, but low cost; local sources are preferred in order to valorize the territory, for examples Barbera grapes and Mentha Piperita of Pancalieri in the case of Piedmont. Polyphenols and essential oils are natural extracts from these types of sources and they have antitumoral, anti-inflammatory, antioxidant and osteoinductive properties and they are also reductive agents useful for the in situ reduction of silver nanoparticles in order to confer antibacterial properties to the surfaces. The substrates used for functionalization were a surface chemical treated bioactive titanium alloy and a silica based bioactive glass. Different functionalization protocols were studied and improved. The procedures of functionalization were tailored for each molecule and both substrates by varying pH, medium, solute concentration and time of functionalization in order to maximize the amount of molecules grafted to the surface and minimize any effect of degradation of the molecules. After functionalization, the samples were physically and chemically characterized and tested in vitro with bacterial and cellular assays. The presence and the activity of the natural molecules on the surface after functionalization was confirmed by means of Fourier Transform Infrared Spectroscopy, X-ray photoelectron spectroscopy, spectroscopic measurements with the Folin&Ciocalteu method, Gaschromatographic analysis and Fluorescence microscope analysis. The cellular tests highlighted the selective actions of polyphenols with tumoral and healthy cells showing cytotoxicity effects on tumoral cells and protective effects against RONS on healthy cells. Bioactivity tests of apatite precipitation in vitro in Simulated Body Fluid and of cellular mineralization show the ability of polyphenols to improve mineralization process. They influence the deposition kinetic of hydroxyapatite deposition kinetic and the formation of different apatite structure depending on the type of polyphenol used for the functionalization. Functionalization with Mentha essential oil shows the reduction of the bacterial adhesion on the treated surfaces tested with Staphylococcus Aureus and the same result was found for the surfaces with the silver nanoparticles. In both cases, it is evidenced that it is challenging to find a proper balance between an effective antibacterial action (bactericide or bacteriostatic) and cytocompatibility.Silver nanoparticles were in situ reduced on the surface of chemically-treated titanium alloy by means of the use of polyphenols as natural reducing agents in order to confer antibacterial activity to the surface. The presence, distribution and shape of the silver nanoparticles were investigated with Field Emission Scanning Electron Microscopy equipped with energy dispersive spectroscopy, as well as Transmission electron microscopy with selected area electron diffraction patterns. The nanoparticles are under the 10 nm and well dispersed on all the surface of the samples. According to the results, surface functionalization of biomaterials is a promising strategy in order to combine the properties of biomolecules with those of surfaces and also to obtain is situ synthesis of antibacterial nanoparticles.