Freeze-drying is commonly used to prepare threedimensional scaffolds (33).
The principle involved is that the polymer solution, emulsion, or hydrogel is frozen to induce phase separation, and the solvent is then removed by vacuum freeze-drying to form a porous scaffold.
The pore morphology, mechanical properties, biocompatibility, and degradability of the scaffold are affected by the concentration of the polymer solution and the phase separation temperature, the quenching temperature, and the types of polymer and solvent.