Classification of Hydrogels and Ferrogels

Hydrogels (HGs) can be categorized based on their internal structure and how they react to outside influences. When physicochemical interactions occur to internal polymer chains, these internal interaction can be reversible. Numerous methods can be used to create these physical hydrogels, including amphiphilic copolymers, protein interactions, crystallization, hydrogen bonding, charge interactions, and stereo-complexing. In contrast, covalent cross-linking might make the internal contact irreversible. Using graft copolymerization, reactive functional groups, and enzymatic techniques, chemically synthesized hydrogels have a high cross-linking density. Furthermore, the pH, external response, temperature, voltage, light, and enzyme have all been used to identify certain smart hydrogels. This chapter goes into a significant depth on the types of hydrogel, including its internal structure and exterior response. Additionally, the discussion sheds light on the origin, structure, method of synthesis, crosslinking process, charge, physical aspect, responsiveness, and degradation-based classification of HGs. Conversely, ferrogels (FGs) are potential candidates for use in engineering and medicine, including actuation and controlled drug delivery, due to their magnetic and elastic interactions. The polymer architecture of magnetic gels will receive particular attention as it controls the degrees of freedom of the magnetic particles in the gel and is essential for the particle-polymer interaction that creates the mechanisms available for the gel deformation in magnetic fields. The chapter describes the various types of ferrogels that have been achieved and gives a summary of the interaction and dispersion mechanism for the ferrogels.