DEVELOPMENT OF SHAPE-MEMORY COMPOSITES BASED ON A BIODEGRADABLE POLYESTER ELASTOMER

Abstract

The current PhD thesis deals with the development and characterization of novel nanocomposites based on biodegradable poly(mannitol sebacate) (PMS) matrices with tailored properties and shape-memory capabilities for biomedical applications. Two types of fillers —cellulose nanocrystals (CNC) and electrospun poly(lactic acid) nanofibers (NF-PLA)— were used as reinforcement in order to induce and/or enhance the shape-memory properties of PMS matrices. Also, different crosslinking profiles and stoichiometric ratios between mannitol and sebacic acid (1:1 and 1:2) were studied and evaluated to obtain samples with low and high degrees of crosslinking. An appropriate combination of the crosslinking profile and the monomer ratio for PMS matrix, as well as the addition of low content of CNC, allowed the development of PMS/CNC nanocomposites with a wide range of mechanical properties and degradation profiles. On the other hand, highly oriented poly(lactic acid) (PLA) nanofiber mats obtained by electrospinning were embedded in the PMS matrices. An enhancement of up to 53-fold in the Young´s modulus was observed for PMS/NF-PLA nanocomposites filled with 15 wt% of PLA nanofibers. The incorporation of fillers (CNC and NF-PLA) allowed the development of thermally active shape-memory nanocomposites with an enhancement of parameters such as recovery stress and shape fixity. The electrospun PLA-reinforced nanocomposites, offered the best balance of mechanical and thermal properties, as well as a greater control of the transition temperature for switching the change of shape, within a useful range of temperatures. Owing to that, these materials may be of interest as smart responsive systems in long-term biomedical applications.