Concentration as a Factor of the Gelatin-Based Hydrogel Mechanical Properties from Gel-Like to Solid-Like Behavior

Hydrogels are soft materials that exhibit mechanical properties between liquids and solids, making them attractive for applications in biomedical engineering, pharmaceutics, and food science. In this work, we studied how the mechanical properties of gelatin-based hydrogels depend on concentration, focusing on the transition from a soft solid with a gel-like behavior to an elastic solid. We prepared hydrated gelatin samples by dissolving determined mass quantities of dry bovine gelatin powder in hot deionized water and allowing them to solidify under reproducible thermal conditions. Compression tests were performed using a custom mechanical press to determine the Young’s modulus and Poisson’s ratio, while torsion pendulum experiments were used to obtain the shear modulus. The results show that concentration plays a critical role in the rigidity and deformation response of the material. For samples with concentrations below approximately 0.075 g/ml, the Young’s modulus and shear modulus remain very low, and the Poisson’s ratio exceeds 0.5, indicating a soft solid behavior dominated by gel-like behavior. In contrast, for concentrations above this threshold, both elastic moduli increase significantly, while Poisson’s ratio gets below 0.5, showing the emergence of an elastic solid network capable of storing mechanical energy. This identifies a clear mechanical transition governed by gelatin concentration, even under constant temperature conditions (24.1？C). The three mechanical properties exhibit consistent trends, confirming that the microstructure of the gelatin network evolves with concentration: weak and sparsely connected chains at low concentrations, and a strongly cross-linked structure at higher concentrations. The identification of critical concentration provides insight into how gelatin hydrogels can be adjusted to achieve desired stiffness, deformability, and stability. These findings contribute to the understanding of soft organic matter and offer a quantitative basis for producing gelatin systems in practical applications. Furthermore, the results are relevant for future research on phononic crystals made from hydrogels, since their elastic properties directly influence mechanical wave propagation and the resulting band structures.