Porous alginate hydrogels: synthetic methods for tailoring the porous texture

Alginate is a versatile, renewable biopolymer that has found numerous applications in diverse areas such as adsorbent materials of water pollutants and scaffolds for tissue engineering. In such kinds of applications the most convenient physical form of alginate-based materials is as porous matrices. The pore scale dimension has to be carefully engineered to meet the requirements posed by the specific application. The aim of this paper is to describe two synthetic methodologies that allow the preparation of alginate porous materials characterized by pores lying in well separated dimension ranges. One process is based on emulsion templating, which consists of dispersing an organic phase into an aqueous solution of alginate in the presence of a suitable emulsion stabilizer and locking in the structure of the continuous phase by chemical cross-linking. This approach required the preliminary degradation of alginate to reduce its molecular weight and, hence, the viscosity of the external phase of the concentrated emulsion. Porous matrices were characterized by pores and interconnects of about 10-20 and 2-5 microm, respectively, and a surface area of 230 m(2)/g. The second process consisted of replacing the organic, internal phase with a gas, namely, CO(2), generated in situ the aqueous solution of alginate. The chemical reaction for CO(2) generation, nature of the surfactant, and cross-linking method were carefully selected to give highly porous, stable matrices with pores and interconnects of the order of 300 and 80 microm, respectively.