**4. Conclusions**

In this chapter, the author has reviewed recent developments in electric- and magnetic-responsive hydrogels from the perspective of materials and properties and applications. Many hydrogels have been employed so far for the fabrication of the hybrid systems comprising natural (e.g., Alg and Col) and synthetic polymers (e.g., PVA and PEG) but mainly a mixture of different polymers to improve the performance of the interpenetrated hydrogel obtained. The different strategies to confer hydrogels with electric and magnetic responsiveness—blending, in situ precipitation, covalent bonding—have been presented. The different methodologies allowed modifying the structure of the hydrogels (e.g., different distribution of the NP within the hydrogel framework) and therefore their properties. The main applications for the electric- and magnetic-stimuli hydrogels have been presented, including tissue engineering, drug delivery, and actuation. It has been shown that the unique presence of the nanomaterials either with electrical conductivity or magnetic properties already improved cell adhesion, proliferation, and differentiation, but it was enhanced even more when the hydrogel was either electrically or magnetically stimulated. These hydrogels can also be used as drug delivery systems with the ability to control the amount of drug release just by modifying the applied signal (e.g., voltage and magnetic field strength). Thus, this field is rapidly emerging with new electric- and magnetic-responsive hybrid hydrogels providing significant advances in the biomedical field. And it has been possible thanks to the versatility in the main components—hydrogels, nanomaterials—providing unique features and properties to the hybrid hydrogels.
