Hydrogels are a solid–fluid continuum where the solid is a polymeric material, and the fluid is water. Hydrogels can imbibe a large amount of water due to the three-dimensional porous network of polymeric solid skeleton. In general, hydrogels can be classified as synthetic (e.g., polyvinyl alcohol (PVA), polyacrylamide, and polyacrylic acid) and naturally derived (e.g., collagen, gelatin, and chitosan) based on their origin. A naturally derived hydrogel could mimic the properties of living tissue and become a suitable candidate for biomedical applications. In the present work, gelatin is considered for further study.
Smart hydrogels are known for altering their properties due to the influence of external stimuli such as temperature, humidity, pH, electric field, and magnetic field. In the present study, the main objective is to synthesize and characterize the behavior of magnetic hydrogels. In order to achieve this, first pure hydrogels are investigated. Based on the observations from experimental and modeling results on pure hydrogels, it can be inferred that the mechanics of hydrogels is mainly governed by their water content. Hydrogels with high water content show hyperelastic behavior, whereas lower water-content hydrogels show viscoelastic behavior. It is also observed that hydrogels having high water content are more prone to failure. Therefore, it is decided to characterize the hydrogels having high water content for further study. Other than water and gelatin, another component is magnetic nano-particles. Magnetic particles can be classified as soft magnetic and hard magnetic particles based on their low and high coercivity values, respectively. Hard magnetic hydrogels can form complex forms. They can be used in biomedical applications such as minimally invasive surgery, drug delivery, and soft robotics. The strontium hexaferrite and cobalt ferrite-based hard magnetic soft hydrogels are prepared and characterized uniquely in this work. In addition, the hybrid hydrogels having intermediate properties were also synthesized and characterized. This study makes an attempt to provide a way to design a hard magnetic gelatin-based hydrogel.