Constitutive modeling for hydrogel with chain entanglements and application to adaptive hydrogel composite structures

Hydrogel is one of typical smart materials and has been used in many engineering applications, such as flexible electronics, flexible robots, and biomedical engineering. Modern industries with complex working environments require hydrogel to have higher strength without losing flexibility. Many published experimental studies focus on the preparation technique of hydrogel composite with high strength and toughness. However, the theoretical investigation into the influence of entanglements on the hydrogel deformation is rarely reported for the structure analysis and deformation mechanism of hydrogel composite, as a purpose to design of hydrogel devices. In this paper, the constitutive model is developed for thermal responsive hydrogel with chain entanglements, based on Flory-Rehner theory and slip-link model, and numerically solved by a user subroutine in ABAQUS. The uniaxial tensile and compressive simulations of standard specimens are carried out to validate the proposed model and demonstrate the applicability of the hydrogel composite, in which a great agreement is obtained by comparing the simulation results to the experimental data from published work. Subsequently, the hydrogel composites with three types of structure, such as hydrogel grippers, scaffolds and skins, are designed to improve the overall strength and maintain the flexibility of the devices, inspired by the deformation mismatch characteristics of multilayer hydrogels. The results show that the properties of composite hydrogels are closely related to the level of entanglements, cross-link and composite structures. This work may contribute to the preparation of reinforced hydrogels and provide insights for the design of hydrogel multifunctional devices.