Gelatin-based hydrogels are a promising candidate in biomedical fields due to their mechanical and chemical characteristics. To explore the various capabilities of gelatin-based hydrogels, it is required to synthesize the hydrogels in the optimized laboratory conditions and find out their mechanical behavior in response to different loading profiles. However, the synthesis and characterization of hydrogels is a very time-consuming process. Therefore, it is challenging to prepare and test the hydrogel specimens for different kinds of loading with repeatable results. In this regard, modeling of hydrogels paves the way to predict the behavior of hydrogels under different types of loading and geometric conditions. In addition to this, it can also be possible to improve the synthesis procedure based on the results obtained from the simulations.
In the present work, the effect of variation of water content on the mechanical properties of gelatin-based hydrogels is investigated through mechanical characterization and mathematical modeling. The pure gelatin hydrogels and gelatin/polyvinyl alcohol-based composite hydrogels having 90%, 70%, and 50% water content are prepared using the solvent casting method. To characterize the mechanical behavior, these hydrogels are subjected to monotonic stretch, constant stretch, constant stress, multistep stretch, and cyclic stretch loading. Based on experimental observations, a phenomenological and micromechanics approach-based mathematical model is proposed to capture the hyperelastic and viscous behavior of the hydrogels. The simulations based on the multistart optimization are performed to obtain the material parameters using the proposed model. The mechanical characterization and the modeling results indicate that the gelatin-based hydrogels show the significant viscoelastic behavior at lower water content (70% and 50%), and it reduced at higher water content (90%).