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 have been developed as temperature-controlled manipulators.  The PNIPAM-clay NC structure provides the hydrogel with excellent mechanical property, and the thermo-responsive bending property of the PNIPAM-clay NC hydrogel is achieved by designing an asymmetrical distribution of nano-clays across the hydrogel thickness.  The hydrogel is simply fabricated by a two-step photo polymerization.  The thermo-responsive bending property of the PNIPAM-clay NC hydrogel is resulted from the unequal forces generated by the thermo-induced asynchronous shrinkage of hydrogel layers with different clay contents.  The thermo-responsive 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 thermo-responsive 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.