Supercritical drying of alginate beads for the development of aerogel biomaterials: Optimization of process parameters and exchange solvents

Conventional hydrogel drying techniques can often induce collapse and shrinkage of the gel nanostructure. In this work, supercritical drying of alginate hydrogel beads is demonstrated to be a very effective process for aerogels production. The process involves solvent exchange followed by supercritical extraction, which prevents the gel from collapsing, while reproducing an aerogel nanostructure that exactly mimics the original hydrogel. Ethanol and acetone were used as water exchange solvents. Using ethanol, the bead spherical shape and nanostructure were most closely maintained when supercritical drying was performed at 150 bar and 38 °C. In addition, the diameter of the dehydrated beads only decreases by 0.6% compared to the hydrated hydrogels. The use of acetone also generated, at almost all the supercritical drying conditions chosen, aerogel with a uniform internal nanostructure, and the lowest shrinkage of 0.3% was obtained operating at 100 bar and 38 °C. A water/ethanol mixture with a ratio of 2:98 also generated aerogel with a homogeneous internal structure at 100 bar and 38 °C. This mixture could potentially be suitable for applications involving proteins loading into an aerogel.