Bilayer-type fluorescence hydrogels with intelligent response serve as temperature/pH driven soft actuators

4D Printing of Shape‐Memory Hydrogels for Soft‐Robotic Functions

“…SMP-based 4D printing offers structural modification and recovery in response to temperature, which are established through complex functionalities of multiple or reversible shape switching, and such printing may provide inspiration for the molecular architecture of shape memory hydrogels (SMHs). [25][26][27][28][29] The first hydrogel-based bilayer actuation system composed of pNIPAM and acrylamide, obtained through conventional mold techniques, was demonstrated by Hu et al; [25] after that, a range of self-assembled, origami-inspired structures were reported, [27,[30][31][32][33][34][35][36][37][38] but only a few works successfully realized 4D printing with hydrogels. [22] Therefore, mechanically active, self-shaping hydrogels that undergo desired, programmable 3D shape transformations and execute mechanical tasks as soft robots under an external trigger have recently attracted growing interest.…”

“…[23,24] Directed movement of hydrogels can be obtained by expansion/contraction, for example, by isotropic volume expansion or shrinkage of homogeneous hydrogels or by the bending/unbending approach, which represents an anisotropic deformation and often involves fabrication of a hydrogel structure with two layers with different swellability values. [25][26][27][28][29] The first hydrogel-based bilayer actuation system composed of pNIPAM and acrylamide, obtained through conventional mold techniques, was demonstrated by Hu et al; [25] after that, a range of self-assembled, origami-inspired structures were reported, [27,[30][31][32][33][34][35][36][37][38] but only a few works successfully realized 4D printing with hydrogels. [28,29] Some noteworthy Hydrogel actuators with soft-robotic functions and biomimetic advanced materials with facile and programmable fabrication processes remain scarce.…”

Composite Polymeric Membranes with Directionally Embedded Fibers for Controlled Dual Actuation

“…[20,21] Soft actuators with bilayer structure have been previously reported. [11,22,23] Their actuation relies on the stimuliinduced anisotropic size change of two attached layers. Li et al [23] have prepared bilayer actuators based on a semiinterpene trating network of poly(Nisopropylacrylamide) (PNIPAm) and poly(diallyldimethylammonium) on a passive layer of polydi methylsiloxane, which can undergo reversible bidirectional bending to grip an object in response to temperature and pH stimuli.…”

“…Soft actuators with bilayer structure have been previously reported . Their actuation relies on the stimuli‐induced anisotropic size change of two attached layers.…”

“…Li et al have prepared bilayer actuators based on a semi‐interpenetrating network of poly( N ‐isopropylacrylamide) (PNIPAm) and poly(diallyldimethylammonium) on a passive layer of polydimethylsiloxane, which can undergo reversible bidirectional bending to grip an object in response to temperature and pH stimuli. Cheng et al have fabricated a four‐arm gripper based on two layers of PNIPAm and poly(2‐(dimethylamino) ethyl methacrylate), which rapidly responses to both temperature and pH. Bassik et al have presented bilayer actuators made of NIPAm and acrylic acid (AA) hydrogel on a passive polyethylene oxide diacrylate layer, which undergo reversible open and close behavior by varying the pH and ionic strength of the aqueous medium.…”