Hierarchical Macroporosity Induced by Constrained Syneresis in Core−Shell Polysaccharide Composites

A radial pattern of macroscopic channels can be generated in core−shell polysaccharide microspheres during gel drying. The mechanical properties and the permeability of the outer crust can be tailored to control the formation of shafts in the organogel. The stiffness of the shell resists the shrinkage of the gel and causes channels to be opened in the direction in which the drying front advances. The permeability of the shell affects the effectiveness of supercritical drying and allows one to control the syneresis of the gel. Examples are provided from a chitosan−silica composite and from Cu-alginate gel beads with chemically modified outer crust.