Novel preparative method for porous hydrogels using overrun process

Porous poly(vinyl alcohol) (PVA) hydrogels were prepared using the overrun process which is usually used in manufacturing ice cream. The pores in the hydrogel formed exhibit dual-pore structure due to the injection of air bubbles and ice recrystallization. Morphological investigation revealed that overrun-processed hydrogels had closed pore structures and that their pore size and size distribution had been influenced by the impeller rate and concentration of polymer solution. The closed-pore structure was reformed into interconnected open-pore structure at lower concentrations of the solution. The freeze-thawing process, which takes place in PVA cross-linking, has no effect on the bubble structure, but removes the small pores formed during ice recrystallization. Besides the swelling ratio of overrun-processed PVA hydrogels is increased tenfold in comparison with non-porous hydrogels. Overrun-processed hydrogels showed more rapid swelling kinetics than freeze-dried and film-like hydrogels due to their larger surface area. In the future, the overrun process can be applied to prepare porous scaffolds containing proteins, such as growth factors and other cytokines, without denaturation, because it operates at a low temperature. (C) 2004 Society of Chemical Industry.