Magnetic nanocomposite hydrogel with ultra-stretchable as strain sensors for monitoring human motion and the change of magnetic field

In recent years, the smart hydrogels have gained much concern in the field of research specially related to flexible strain sensors because they exhibit many types of smart interactions that can be useful in wearable devices. However, the conventional hydrogels have poor electrical conductivity that affect the performance of the sensors, so it remains a challenge to achieve noncontact signal monitoring (e.g., for the detection of magnetic field changes). In this study, an ultra-stretchable and magnetically responsive conductive hydrogel was fabricated by adding magnetic ferric tetroxide@polypyrrole composite nanoparticles (Fe 3 O 4 @PPy NPs) to polyacrylamide (PAm). The nanoparticles were easily agglomerated and improved the compatibility of PPy and hydrogel. The obtained PAm/Fe 3 O 4 @PPy hydrogel showed an ultra-stretchability of (961%), a low elastic modulus of (87.8 kPa), and an excellent toughness of (1010.5 kJ m −3 ). Moreover, PAm/Fe 3 O 4 @PPy hydrogel also exhibited a high electrical conductivity of 0.34 S m −1 , and the PAm/Fe 3 O 4 @PPy hydrogel sensor could detect human motions (such as bending of finger, bending of wrist) and muscle micromotion (such as pronouncing). In addition, it can also monitor the change in magnitude of magnetic field.