Weight, mechanical and structural changes induced in alginate gel beads by DC electrical field

Alginate beads were interposed between a pair of electrodes and a DC current was applied. A special custom-made apparatus enabled the use of different shaped anode electrodes. Surface areas of the anodes were never more than twice the projection area of the untouched beads. There was no difference in bead shrinkage among the different alginates used to produce them. At 10-20 V (equivalent to field intensities of 25-50 V/cm), weight losses of 46-60% of initial weight were observed within 10 s. Weight loss was dependent on the concentrations of the alginate and cross-linking agent: the higher the osmotic pressure produced by various salts within the immersion liquid, the smaller the weight loss. Pores were produced within the beads and the affected area of the bead resembled the shape of the electrode. In general, electrically induced shrinkage of the gel caused its texture to strengthen. This phenomenon is in correlation to other mechanisms whereby beads become stronger as a result of imposed shrinkage. Rapid reductions in bead size could be beneficial to immobilization, encapsulation and directed slow-release operations.