Fig. 1: Schematic for topological evolution of CaCO3 particles into MH-HISs under physiologically relevant conditions through ion-exchange reactions.

Solid CaCO3 particles are converted sequentially to CaCO3/MH core-shell, CaCO3/MH yolk-shell, and MH hollow structures through precisely controlled ion movement and exchange of Ca2+ and metal ions (M3+) under biocompatible conditions. Enzymes are encapsulated in the shells for multienzymatic cascade reactions.