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)