To develop a non-destructive quantitative evaluation method for hydrogel, we demonstrated fundamental study for electrical impedance method by use of gelatin hydrogel. We made the gelatin hydrogel which differed in concentration of gelatin to add gelatin powder into saline solution. Also, to investigate the relation between electrical impedance and structure, cross-linked gelatin gels were prepared with formaldehyde. After that electrical impedance measurement, compression test, and water content measurement were carried out. Electrical impedance of gelatin gel was decreased with increasing water content. At the same water content, electrical impedance of cross-linked gelatin gel was higher than that of intact one. Also, we found the relation between electrical impedance and compressive stiffness for gelatin gel. These findings shows that electrical impedance for biopolymer gel was affected by water condition of electrolyte solution where exists in the network of biopolymer chain, electrical impedance method could evaluate quantitatively the change of the structure for hydrogel.
