Dottorato in SCIENZE CHIMICHE

Titolo della tesi: Materiali compositi a base polimerica per applicazioni biomediche e/o industriali

Composite polymeric materials are among of the most recent innovations largely applied as systems for food packaging, tissue engineering, bioremediation, automotive and textiles industries. The use of sustainable materials for the composite preparation is of extreme importance. In this framework, polysaccharides like chitosan (CS) are promising materials thanks to their outstanding properties. However, their poor mechanical resistance and dimensional stability in aqueous medium strongly reduce polysaccharide applicability. Crosslinking of polymers and their conjugation/combination with fillers have proven to be very advantageous strategies for improving polysaccharide performance. Therefore, in this research, chitosan-based composite systems were investigated for application in the medical and analytical fields. To this aim, different modification strategies of chitosan were employed, including dimensional stabilisation processes by cross-linking with different types of crosslinkers and improvement of mechanical properties by nanometric fillers such as graphene oxide (GO). Specifically, porous scaffolds by conjugation of CS with GO at different oxidation degree and content for tissue engineering were obtained. The influence of these two parameters on scaffold performance was investigated. The prepared GO/CS scaffolds were highly porous and showed good water uptake. It was verified that the scaffold thermal stability and mechanical strength increased with GO content increasing, especially when GO at low oxygen content was used. In addition, such GO (at less content of oxygen) provided the scaffold with the best biocompatibility. To improve mechanical resistance of CS based scaffolds, ionic or covalent crosslinking reactions with different amount of crosslinkers, tripolyphosphate polyanion (TPP) and poly(ethylene glycol) diglycidyl ether (PEGDE) respectively, were carried out, also varying CS concentration (1 and 2% w/v). It was evidenced that the crosslinking reactions reduced CS hydrophilicity. The scaffolds obtained with TPP had a porosity lower than that obtained with PEGDE but better mechanical properties, particularly when a low CS concentration together with more severe TPP crosslinking reaction conditions were used. In this latter case, a good biocompatibility was also obtained. To develop composite systems for environmental applications, CS and GO (GO amount from 1% to 20% w/w), were mixed to prepare membranes to be used as absorbent materials for solid-phase extraction of pesticides (SPE). To better stabilize the membranes in water, they were superficially crosslinked with glutaraldehyde. To verify the effect of another crosslinker on the pesticide extraction capacity by membranes, the crosslinking reaction was also performed in bulk with PEGDE on samples containing the highest GO amount. However, this latter sample showed poor performance when tested for the extraction of 21 pesticides with different log Kow. On the contrary, the increased aqueous medium dimensional stability, together with the presence of high GO amounts, made the composite membranes crosslinked with GLU suitable for the preconcentration of different hydrophilic/hydrophobic pollutants. Finally, two different types of molecularly imprinted chitosan-acrylate based hydrogels were prepared for the selective extraction of pesticides. It was found that the amount of template used for imprinting process together with the different permeability of the matrix were the key factors driving the analyte uptake process.