Tunable Physical Properties of Starch-Based Hydrogels Synthesized by Freeze-Thaw Technique

Hydrogels are three-dimensional (3D) polymer networks that are water-absorbent, insoluble, flexible, and biocompatible. The freeze-thaw technique is a physical cross-linking method for hydrogel synthesis, which can form a stable structure and non-toxic materials. Biopolymer hydrogel is a solution to environmental pollution due to synthetic polymers, which have been widely used as hydrogel base materials. This paper uses starch composite as precursor solutions for the preparation of hydrogels. The precursor solution ratios (potato starch/gelatin) of 20:0, 20:1, 20:2, 20:3, and 0:20 were labeled as SCG1, SCG2, SCG3, SCG4, and SCG5, respectively. Morphological results showed a cross-linking between polymer chains (solid area) and porosity (liquid area). During the freeze-thaw process, gelatin interfered with a cross-linking process of the hydroxyl group so that the solid phase decreased and the pore size was irregular and enlarged. The swelling degree increased with the gelatin composition, while the weight loss showed the opposite result. SCG1 showed the highest swelling degree value of around 319.39 ± 35.05a % and lower weight loss of about 19.26 ± 9.91a %, which showed a higher degradability. SCG1 has good mechanical properties with Young Modulus, onset strain, and onset stress of about 1.4 ± 0.33a KPa, 145.11 ± 47.28b %, and 1.62 ± 0.08c KPa, although the highest compressive strength was shown by SCG5 of 25.63 ± 2.75a KPa. In general, we found that the physical properties of starch hydrogels showed a potential to be used as a functional food matrix: higher swelling degree, modulus elasticity, and degradability. For gelatin hydrogels, it is necessary to modify the process to become a potential matrix as a media delivery.