Abstract
Surface charge is one of the most significant properties for the characterisation of a biomaterial, being a key parameter in the interaction of the body implant with the surrounding living tissues. The present study concerns the systematic assessment of the surface charge of electrochemically anodized TiO2 nanotubular surfaces, proposed as coating material for Ti body implants. Biologically relevant electrolytes (NaCl, PBS, cell medium) were chosen to simulate the physiological conditions. The measurements were accomplished as titration curves at low electrolytic concentration (10−3 M) and as single points at fixed pH but at various electrolytic concentrations (up to 0.1 M). The results showed that all the surfaces were negatively charged at physiological pH. However, the zeta potential values were dependent on the electrolytic conditions (electrolyte ion concentration, multivalence of the electrolyte ions, etc.) and on the surface characteristics (nanotubes top diameter, average porosity, exposed surface area, wettability, affinity to specific ions, etc.). Accordingly, various explanations were proposed to support the different experimental data among the surfaces. Theoretical model of electric double layer which takes into account the asymmetric finite size of ions in electrolyte and orientational ordering of water dipoles was modified according to our specific system in order to interpret the experimental data. Experimental results were in agreement with the theoretical predictions. Overall, our results contribute to enrich the state-of-art on the characterisation of nanostructured implant surfaces at the bio-interface, especially in case of topographically porous and rough surfaces.
Highlights
Titanium and its alloys are generally considered suitable materials for metallic implants [1, 2], even though they lack per se in terms of biocompatibility, due to their intrinsic inertness
Lorenzetti et al Nanoscale Research Letters (2016) 11:378 specific diameters by optimising experimental parameters during electrochemical anodization. Such structures were shown to be highly valuable for biological applications from the point of increased surface area and possibility to be used as reservoirs for medications, and for the selective attachment of proteins, which further dictate adhesion of cells
It has been previously shown [11] that binding of proteins is highly influenced by the size of the nanotube diameter, which is due to the increased surface area and to the possibility of proteins to enter into the narrow interior of the nanotubes
Summary
Titanium and its alloys are generally considered suitable materials for metallic implants [1, 2], even though they lack per se in terms of biocompatibility, due to their intrinsic inertness. Lorenzetti et al Nanoscale Research Letters (2016) 11:378 specific diameters by optimising experimental parameters during electrochemical anodization. Such structures were shown to be highly valuable for biological applications from the point of increased surface area and possibility to be used as reservoirs for medications, and for the selective attachment of proteins, which further dictate adhesion of cells. It has been previously shown [11] that binding of proteins is highly influenced by the size of the nanotube diameter, which is due to the increased surface area and to the possibility of proteins to enter into the narrow interior of the nanotubes (only smaller proteins can enter the NTs 15 nm diameter interior). Different nanotube diameters could play an important role in the designing of implantable devices, as it is possible to selectively promote the growth of one cell type over another
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