Production of Nanoporous Materials (Aerogels) From Natural Polymers for Life Science Applications Using Supercritical Fluid Technology

Natural polymers and derivatives are attractive feedstocks for life science applications (e.g., pharmaceutics, tissue engineering, cosmetics, food, biotechnology, agriculture) because of their usual biodegradability, biocompatibility, stability, availability and renewability. Moreover, the portfolio of existing natural polymers presents a large variety of functional groups (e.g., carboxylic, sulfonic, hydroxyl, amino groups), ionic behaviors (anionic, cationic, non-ionic) and biodegradation profiles. This set of properties is a promising starting point for the development of tailor-made materials for controlled release of active substances in different administration routes. Aerogel technology based on gel extraction with supercritical fluids is herein presented as a robust processing approach to obtain lightweight dry nanoporous materials (ρ=0.05-0.3 g/cm³) from natural polymers with outstanding surface area (S_a=100-700 m²/g), open porosity (ε=90-99 %) and loading capacity of compounds. Natural polymers can undergo gelation by different external stimulii (temperature, counterions, covalent cross-linkers) using sol-gel technology. Then, these wet gels can be turn into an aerogel by using a drying technology able to preserve the original nanoporous structure of the said gel in a dry form. In this work, the preparation of aerogels from natural polymers by using gel extraction with supercritical fluids is presented. Materials engineering and step-by-step process optimization allowed the development of a generic processing approach to get aerogels from natural polymers with customized morphologies (cylinders, beads and microspheres) and textural properties (surface area, mesoporosity). The technology was implemented for polysaccharides with different gelation mechanisms (ionotropic, thermotropic) with excellent results: polysaccharides with the highest reported internal surface area were obtained. The thus obtained materials were tested for their use as active agents carriers by supercritical CO₂-assisted impregnation, showing the ability to adsorb a large amount of API (up to 20 wt%) and the ability to stabilize them in the amorphous form. Such materials are especially promising as drug carriers for dry powder inhalation, since their flowability and aerodynamic diameter are significantly improved by the supercritical drying.