• polyelectrolyte complexes
• hydrogels
• food packaging
• biomedical applications
• polyglutamic acid
• ulvan

Polysaccharides represent an important class of natural polymers that possess features, such as biocompatibility, biodegradability, low cost and abundance in nature, which makes them good candidate for the preparation of scaffolds for biomedical applications. In the present thesis our interests was focused on ulvans, a new class of polysaccharides extracted from green algae belonging to Ulva species whose added value is represented by the possibility to obtain them from natural, abundant and renewable resources. Our aim was to test the feasibility of using this material as polymeric matrix for biomedical applications. To this purpose ulvan needs to be crosslinked in the form of three dimensional scaffold of appropriate porosity and water affinity to support cell metabolic functions. Two different strategies were undertaken to prepare ulvan-based hydrogels namely covalent and physical crosslinking. Covalent crosslinking was obtained by UV photopolymerization of the ulvan macromer after proper functionalization with methacryloyl groups. The same technique was used to conjugate bioactive molecules onto ulvan scaffold to enhance its biocompatibility. To this aim a molecule mimicking the Arginine-Glycine-Aspartic acid sequence (RGDm) containing a photopolymerizable group and the gelatin macromolecule grafted with methacryloyl groups were successfully employed. Ulvan-based scaffolds were easily obtained by physical crosslinking through the preparation of Polyelectrolyte Complexes (PECs) between ulvan and chitosan as components. Biological assays on these PECs provided the best results in term of cell viability and proliferation. The developed materials were thoroughly characterized by conventional methods to determine both the chemical modification occurring during crosslinking and the physical properties of the obtained hydrogels such as porosity, rheological behaviour and water affinity. Their biological properties were deeply investigated to test the feasibility of using these materials in biomedical applications.
Over the last decades, the use of polymers as food packaging materials has increased enormously due to their advantages over other traditional materials. In particular a growing interest is devoted to the development of materials from biodegradable biopolymers, particularly those derived from renewable resources. Our interests was focused on poly-γ-glutamic acid (γ-PGA), a biocompatible and biodegradable polymer obtained by microbial fermentation. The main drawback for using plain γ-PGA in food packaging is represented by its high hydrophilicity due to the high content of carboxylic groups. Moisture and water represent the typical environment surrounding food packaging materials. To this aim such matrices need to be stable in those conditions. Our strategy aimed at reducing γ-PGA hydrophilicity by conjugating it with a hydrophobic polymer. Polycaprolactone (PCL) was selected as hydrophobic copolymer in virtue of its reported biocompatibility and biodegradability. Different synthetic strategies have been investigated to graft polycaprolactone onto the carboxyl group of γ-PGA. Most of the envisaged approaches revealed unsuccessful due to the low reactivity of the terminal groups of PCL. The direct conjugation of the two polymers catalyzed by the addition of p-toluensulfonic acid proved to be the most promising approach as evidenced by 1H-NMR analysis of the obtained product.