Advances in biomimetic stimuli responsive soft grippers

Abstract

A variety of biomimetic stimuli-responsive soft grippers that can be utilized as intelligent actuators, sensors, or biomedical tools have been developed. This review covers stimuli-responsive materials, fabrication methods, and applications of soft grippers. This review specifically describes the current research progress in stimuli-responsive grippers composed of N-isopropylacrylamide hydrogel, thermal and light-responding liquid crystalline and/or pneumatic-driven shape-morphing elastomers. Furthermore, this article provides a brief overview of high-throughput assembly methods, such as photolithography and direct printing approaches, to create stimuli-responsive soft grippers. This review primarily focuses on stimuli-responsive soft gripping robots that can be utilized as tethered/untethered multiscale smart soft actuators, manipulators, or biomedical devices.

Keywords: Bio-MEMS; Intelligent systems; Self-folding; Soft actuators; Soft robots.

Fig. 1

Biomimetic soft gripping robots composed of stimuli responsive hydrogels, polymer, or hybrid combination of them. a N-isopropylacrylamide (NIPAM)-modulated thermal responsive bigel stripped grippers (reproduced with permission [17]. Copyright 1995, AAAS). b Poly(N-isopropylacrylamide-acrylic acid)(pNIPAM-AAc) soft gripper that reversibly actuates when triggered by temperature or pH (reproduced with permission [13]. Copyright 2014, IOP Publishing). c Thermally responsive self-folding bilayer soft gripper that closes and opens reversibly when passing by LCST at 36 °C (reproduced with permission [9]. Copyright 2015 American Chemical Society). d Reversible four-state shape changes of soft grippers during heating and cooling process (reproduced with permission [26]. Copyright 2018 Wiley–VCH)

Fig. 2

Biomimetic stimuli responsive soft grippers composed of poly N-isopropylacrylamide (pNIPAM) based hydrogels hybridized with nanoparticles. a Programmable folding cube composed of single-walled carbon nanotube (SWNT)-pNIPAM and low-density polyethylene (LDPE) bilayer that actuates reversibly in water (reproduced with permission [66]. Copyright 2011, American Chemical Society). b Multi near-infrared light (NIR), ionic strength (IS), and temperature change responsive soft gripper composed of graphene oxide (GO)-pNIPAM and pNIPAM-poly(methylacrylic acid)(PMAA) bilayer (reproduced with permission [65]. Copyright 2016, Wiley–VCH). c Thermoresponsive biomimetic flower shaped fluorescent color displaying soft gripper composed of graphene oxide (GO)-pNIPAM and pH responsive perylene bisimide-functionalized hyperbranched polyethylenimine (PBI-HPEI) hybrid bilayer (reproduced with permission [68]. Copyright 2017, Wiley–VCH). d Temperature-controlled pNIPAM/pNIPAM-co-clay nanocomposite bilayer hydrogel gripper that grips a moving pearl (reproduced with permission [22]. Copyright 2015, Wiley–VCH)

Fig. 3

Photothermal responsive liquid crystalline networks (LCNs) and liquid crystalline elastomers (LCEs) soft grippers. a Photothermal actuation of 4- or 8-armed soft grippers when exposed to 460 nm illumination that are composed of splay- or − 90° twisted nematic alignment patterns in a liquid crystal polymer networks film (reproduced with permission [75]. Copyright 2017, Wiley–VCH). b Flytrap mimetic light responsive self-folding liquid crystal elastomers (LCEs) gripper that captures an object according to light illumination intensity feedback (reproduced with permission [76]. Adapted with permission under the terms of the Creative Commons Attribution Non Commercial License 4.0 license. Copyright 2017, The Authors). c Water Lily flower mimicked thermoresponsive soft liquid crystal networks (LCNs) grippers that can open and close via induced smetic–nematic phase transition in LCNs according to heating and cooling process (reproduced with permission [7]. Copyright 2018, American Chemical Society). d Light driven actuation of LCNs soft grippers controlled by the mesogen alignment change (reproduced with permission [28]. Copyright 2017, Wiley–VCH)

Fig. 4

Two main photolithographic and 3D printing methods to fabricate stimuli responsive soft grippers. a Process flow of photolithography to create stimuli responsive soft grippers with following two-step UV exposures. The photopatterned bilayer soft grippers that close on heating and open up on cooling reversibly (reproduced with permission [79]. Copyright 2018, IEEE). b Photolithographically patterned biodegradable soft grippers that respond to temperature change (reproduced with permission [83]. Copyright 2019, American Chemical Society). c 4D printing that creates thermally responsive shape morphing flower shaped grippers composed of cellulose fibrils alignments programmed hydrogel composite ink (reproduced with permission [93]. Copyright 2016, Springer Nature). d 3D printed shape morphing soft grippers that pick-and-place a light ball (reproduced with permission [25]. Copyright 2018, American Chemical Society)

Fig. 5

Tethered soft grippers as smart actuators or manipulators. a Pneumatically driven tethered soft gripping robot that provides a range of complex motions by curling upwards or downwards controlled by expansion and contraction in elastomeric structures (reproduced with permission [15]. Copyright 2011, Wiley–VCH). b X-shaped ion-printed tethered electrical assistant soft gripper that presents rapid grasp a target in ethanol and releases it in water reversibly (reproduced with permission [99]. Copyright 2013, Springer Nature). c Optically and sonically camouflageable hydraulic hydrogel gripping robot that holds and releases a live goldfish noninvasively (reproduced with permission [100]. Adapted with permission under the terms of the Creative Commons Attribution Non Commercial License 4.0 license. Copyright 2017, The Authors). d Stimuli responsive ion dip dyeing and transfer printed tough hydrogel-based soft gripper that can fold to grip a target in water and release it in ethanol reversibly (reproduced with permission [101]. Copyright 2016, Wiley–VCH)

Fig. 6

Untethered soft grippers as smart actuators or manipulators. a Thermomagnetically responsive untethered soft gripper that detects and sorts differently colored beads in the respectively colored drop areas autonomously (reproduced with permission [57]. Adapted with permission under the terms of the Creative Commons Attribution Non Commercial License 4.0 license. Copyright 2017, The Authors). b Shape programmable DNA-crosslinked untethered soft gripper that presents shape morphing in response to external programmed DNA hairpin sequences (reproduced with permission [102]. Copyright 2017, AAAS). c Bifurcation mismatch strain driven shape transformation of stimuli responsive soft gripper that has no hinges in a thin bilayer structure (reproduced with permission [8]. Copyright 2018, Wiley–VCH). d Demonstration of the universal pick up, transport, release, and recovery process of a soft robotic microgripper (reproduced with permission [21]. Copyright 2018, Wiley–VCH)

Fig. 7

Stimuli responsive soft grippers for biomedical drug delivery or surgical biopsy. a Thermoresponsive self-folding microgrippers that can capture yeast cells by the deswelling induced contraction in the thermoresponsive layer that results in bending of the soft gripper at low temperature (reproduced with permission [18]. Copyright 2011, The Royal Society of Chemistry). b Therapeutic soft gripper that can grasp a clump of cells and demonstrate the endoscopic in vivo food dye delivery test to porcine stomach (reproduced with permission [10]. Copyright 2014, Wiley–VCH). c Biodegradable thermomagnetically responsive soft gripper for drug delivery (reproduced with permission [83]. Copyright 2018, American Chemical Society). d Self-folding thermo-magnetically responsive soft gripper that can capture and excision of cells from a live fibroblast clump (reproduced with permission [9]. Copyright 2015, American Chemical Society)