Aerogel based formulation by supercritical drying of alginate beads

Conventional hydrogel drying techniques can induce the gel nanostructure collapse. In this work supercritical drying of alginate hydrogel beads was demonstrated to be a very effective process for alginate aerogels production: solvent exchange followed by supercritical extraction avoided gel collapse and an accurate reproduction of the nanostructure was maintained in the derived aerogel. Ethanol and acetone were used as water exchanging solvents; when ethanol was used, the best reproduction of aerogel internal morphology was obtained operating at 150 bar and 38°C. A uniform internal nanoporous structure and well defined spherical bead shape was obtained. A shrinkage of only 0.6% with respect of the diameter of the hydrated beads was observed. Acetone generated at all drying conditions chosen, aerogels with an uniform internal nanostructure; in this case, the best results in terms of internal morphology and lowest shrinkage (0.3%) were obtained operating at 100 bar and 38°C. Water/ethanol mixture with a ratio of 2:98 also produced a homogeneous internal structure at 100 bar and 38°C; this mixture can be suitable for bioactive compounds loading in the aerogels.