Effect of Cellulose Nanocrystals and Starch on the Shape-Memory Behavior of Biodegradable TPU-Based Ternary Polymer Composites

Integrating shape-memory functionality with controlled biodegradability is essential for developing sustainable polymeric materials for biomedical and soft-actuation applications. This study investigated the effect of incorporating cellulose nanocrystals and starch in thermoplastic polyurethane (94% bio-based), synthesized via one-shot solvent-free polymerization using 71% bio-based 1,5-pentamethylene diisocyanate, 100% bio-based polytrimethylene ether glycol, and 1,3-propanediol. Cellulose nanocrystals were added to the combinations at 0.5, 1, and 2 wt.%, and starch at 1 wt.%. TPU_CNC_2 recovered fully to its original shape in 15 seconds at 90°C, TPU_CNC_2_Starch_1 retained 98 ± 1.9% in 60 seconds at 80°C, and 95 ± 2.2% in 15 seconds at 90°C with a tensile strength of approximately 20 ± 1.2 MPa, an elongation at break of 2891 ± 20.9%, and a moderate Shore A hardness of 67. Moreover, Cell viability was also assessed on day 5; all developed samples showed approximately 90 ± 2.2% cell coverage on the sample surface, with TPU_CNC_2_Starch_1 achieving 99 ± 1% coverage. FIB-SEM analysis confirmed the incorporation of CNC and the pore structure after 8 weeks in PBS of pH 7.4. Additionally, biodegradation was investigated in PBS solution, where starch-containing samples, such as TPU_Starch_1 and TPU_CNC_2_Starch_1, lost approximately 16 ± 1.3% of their weight over 8 weeks. These findings demonstrate a rapid recovery, cytocompatibility, and partial biodegradability of a bio-based thermoplastic composite for biomedical devices, soft actuators, and environmentally responsible packaging.