Evaluation of new nanocomposite material for the consolidation of ancient bone

Resumen

The present investigation is focused on the preparation and characterization of polymer composite materials based on a) polysulfone (PSF) filled with nanoparticles of hydroxyapatite (HA) and b) polysulfone (PSF) filled with nanoparticles of zinc oxide (ZnO). More specifically, the use of airbrushing will be explored as a method of applying these materials, for the treatment of archaeological bones, i.e., for the restoration and consolidation of historical bones. The first objective of this research is to prepare the polysulfone filled with different amount of hydroxyapatite nanoparticles (0%, 1%, 2%, 5% and 10% weight) in form of a transparent film from the use of a simple commercial airbrush. Then, deep characterization of the materials allowed collecting information enough to understand the role the nano filler/polymer matrix interphase plays in the final performance of the materials concerning some potential applications. Structural studies done by infrared spectroscopy revealed little interactions between the PSF and HA in the composites since no band shifts or significant absorbance bands ratios observed in the spectra. On the other hand, although the presence of HA did not significantly affect the glass transition temperature of the composites, as observed by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) showed that the filler decelerated thermal degradation. Besides, the mechanical behavior of the composites was studied by tensile tests leading to some interesting results. For small amounts of HA particles, up to 1%, %wt, the elastic modulus of the composites was higher than the upper bound predicted by the rule of mixtures. This result was interpreted in terms of the contribution of a high-volume fraction of a third proposed component, the interphase region. At a certain content of particles, the interphases arising from different particles can collide, favoring particle aggregates and consequently leading to a decrease of the interphase contribution. However, for higher loadings, the introduction of a more rigid filler may become the main factor affecting elastic properties. In fact, for these PSF/HA reinforced composites, an efficiency factor, K, was calculated to estimate the reinforcing efficiency of the nanoparticles in the composite and a decrease of K was observed with the amount of nanoparticles, which can be interpreted in terms of a decrease in the reinforcing effect of the interphases generated in this composite material. In the second part of the research, a system based on polysulfone, PSF, filled with ZnO nanoparticles (1%, 2%, 5% and 10% by weight) in form of films was prepared and characterized. The structure and morphology of the resulting nanocomposites were investigated by Attenuated Total Reflectance - Fourier Transform Infrared Spectroscopy – (ATR - FTIR) and scanning electron microscopy (SEM), respectively. On the other hand, thermal properties of PSF nanocomposites were studied by thermogravimetric analysis and differential scanning calorimetry while mechanical behaviour was studied by carrying out tensile tests and analyzing elastic modulus. The ATR-FTIR spectra did not show any structural variation in the polymer pointing out the lack of chemical or specific interactions between ZnO nanoparticles and polymer chains. SEM images of PSF/ZnO nanocomposites showed that airbrushing is a good method to prepare the materials with relatively good dispersion of the filler within the polymer. Micrographs obtained by SEM showed that the neat PSF has a smooth, uniform, and homogeneous surface and when ZnO nanoparticles were added the surface properties and texture of the nanocomposite polymeric film changed dramatically. Finally, the use of polysulfone-based nanocomposites filled with hydroxyapatite (HA) and zinc oxide (ZnO) particles as possible materials used for bone consolidation was investigated. Using a commercial airbrush, the bone samples were treated with the different polymeric systems with different contents of HA and ZnO (0%, 1%, 2%, 5%, 10%, % by weight). The morphology of the materials was studied by optical microscopy (OM) and by scanning electron microscopy, SEM, and the mechanical properties were studied from the measurement of Martens hardness. Morphological characterization showed a uniform surface treatment without any detectable surface whitening, even at high particle concentrations (up to 10%, % by weight). SEM images demonstrate that the use of the airbrush allows coating the bone specimens with smooth and homogeneous thin films of both system PSF/HA and PSF/ZnO having an excellent distribution of nanoparticles in the polymer matrix. Surface mechanical characterization was carried out to measure Martens Hardness of the treated specimens. It was found that the treatment with the polysulfone coating itself is an effective method to protect the surface of the materials since an increase in MH was observed too. Airbrushing treatment of the ancient bone with PSF/HA solutions increased locally bone hardness, being enhanced by increasing amounts of nanoparticles. Also, a small amount of 1% of ZnO nanoparticles is enough to modify the mechanical properties of the matrix without losing other properties such as optical properties, which is very important for applications of these materials in the restoration and consolidation of bones. These results suggest that the bionanocomposite PSF/HA (5%) and antibacterial nanocomposite PSF/ZnO by 1% ZnO may be a good alternative for use as an alternative material for the consolidation and conservation of ancient bone. In the end, the materials considered in this study are promising alternatives for applications in the restoration and conservation of the cultural property, particularly for bone consolidation and conservation.