Constitutive model for nonlinear anisotropic swelling and self-growing of polymers and gels

Due to exceptional swelling properties, gel polymers can form shape-deforming structures, rendering them suitable for applications. Research on dynamic polymers and polymer gels has developed several novel mechanisms beyond the swelling mechanism. These novel mechanisms also enable dynamic polymers to undergo shape transformations over time within a solution environment. Specifically, under certain environmental conditions, monomer solutions can undergo monomer insertion and facilitate the formation of new polymer chains. This process endows the polymer gel network with self-growing characteristics, making it better suited to meet the demands of applications in engineering. Introducing anisotropy into hydrogels makes it possible to meet the demands for non-uniform deformation of polymer gel structures in many scenarios, thereby facilitating the programmable anisotropic swelling. Although the potential applications of these technologies are extensive, many aspects of the self-growth and swelling deformation behaviors in anisotropic polymer gels remain underexplored. A micro-theoretical investigation into the self-growth process of fiber-reinforced polymer gels is proposed. The embedding of fibers within the growable polymer matrix is shown to guide the material toward exhibiting overall anisotropic behavior. To describe this response in detail, a constitutive model for self-growing fiber-reinforced polymer gels was developed and implemented through numerical simulations, which provides a theoretical foundation for predicting the complex deformation behaviors of anisotropic biomaterials.