Tuning properties of fibroin-based materials: effect of freezing cycles on shape memory of hydrated cryogels and a comparative analysis of drying techniques on dried material performance

This study addresses the development of hydrated silk fibroin cryogels and their subsequent drying using a sustainable approach in which water is the only solvent, offering a simple and environmentally friendly processing route. The effects of key parameters, including the number of freeze-thaw cycles (1, 2, and 3) and freezing temperatures (-20 °C and - 80 °C), on the shape memory behavior of hydrated cryogels were systematically investigated. The influence of two drying techniques, supercritical CO₂ drying and freeze-drying, on the structural, thermal, and mechanical properties of the dried materials was also evaluated. The freeze-thaw process generated materials with highly organized porous structures, such as the honeycomb-like structures obtained at -20 °C, which provided elastic behavior and good structural stability, showing the strong impact of processing conditions on polymer network formation. The hydrated cryogels displayed sponge-like properties and excellent shape memory after two or more freeze-thaw cycles, almost completely recovering their original dimensions after compression and rehydration. Compression tests confirmed the elastic nature of hydrated cryogels, as they tolerated repeated compression without significant structural failure, highlighting their potential in applications requiring cyclic compression. Supercritical CO₂ drying proved to be the most effective method in preserving the porous structure and enhancing mechanical strength. Aerogels prepared by this technique exhibited superior mechanical performance compared to freeze-dried samples, showing greater resistance to deformation and improved structural stability. Overall, these materials emerge as promising candidates for a wide range of applications, from smart devices to sustainable and high-performance materials.