Poly(N-isopropylacrylamide)-Clay Nanocomposite Hydrogels with Responsive Bending Property as Temperature-Controlled Manipulators

Novel poly(N-isopropylacrylamide)-clay (PNIPAM-clay) nanocomposite (NC) hydrogels with both excellent responsive bending and elastic properties are developed as temperature-controlled manipulators. The PNIPAM-clay NC structure provides the hydrogel with excellent mechanical property, and the thermoresponsive bending property of the PNIPAM-clay NC hydrogel is achieved by designing an asymmetrical distribution of nanoclays across the hydrogel thickness. The hydrogel is simply fabricated by a two-step photo polymerization. The thermoresponsive bending property of the PNIPAM-clay NC hydrogel is resulted from the unequal forces generated by the thermoinduced asynchronous shrinkage of hydrogel layers with different clay contents. The thermoresponsive bending direction and degree of the PNIPAM-clay NC hydrogel can be adjusted by controlling the thickness ratio of the hydrogel layers with different clay contents. The prepared PNIPAM-clay NC hydrogels exhibit rapid, reversible, and repeatable thermoresponsive bending/unbending characteristics upon heating and cooling. The proposed PNIPAM-clay NC hydrogels with excellent responsive bending property are demonstrated as temperature-controlled manipulators for various applications including encapsulation, capture, and transportation of targeted objects. They are highly attractive material candidates for stimuli-responsive smart soft robots in myriad fields such as manipulators, grippers, and cantilever sensors.