Untethered Recyclable Tubular Actuators with Versatile Locomotion for Soft Continuum Robots

Abstract

Stimuli-responsive materials offer a distinguished platform to build tether-free compact soft robots, which can combine sensing and actuation without a linked power supply. In the past, tubular soft robots have to be made by multiple components with various internal channels or complex cavities assembled together. Moreover, robust processing, complex locomotion, simple structure, and easy recyclability represent major challenges in this area. Here, it is shown that those challenges can be tackled by liquid crystalline elastomers with allyl sulfide functional groups. The light-controlled exchange reaction between allyl sulfide groups allows flexible processing of tubular soft robots/actuators, which does not need any assisting materials. Complex locomotion demonstrated here includes reversible simultaneous bending and elongation; reversible diameter expansion; and omnidirectional bending via remote infrared light control. Different modes of actuation can be programmed into the same tube without the routine assembly of multiple tubes as used in the past. In addition, the exchange reaction also makes it possible to use the same single tube repeatedly to perform different functions by erasing and reprogramming.

Reprocessable Thermoset Soft Actuators

“…For another example, we could make robust tubular actuator (Figure c) and subuliform actuator (Figure d) with reversible expanding‐shrinking actuation by aligning the LCET sheet, rolling up and welding the overlap. Tubular actuators show great potentials in soft robotics, as artificial blood vessels and so on . Welding aligned LCET strips together provides a simple method to build net‐like actuators, whose pores enlarge in the liquid‐crystal phase and shrink in the isotropic phase (Figures e,f).…”

Light‐Responsive Shape‐Changing Polymers

“…As reshaping is a common challenge in crosslinked materials (including LCEs and LCNs), researchers have started to develop novel classes of crosslinked polymers with rearrangeable networks. The exchangeable bonds reported for LCP materials mainly come from ester, disulfide, and allyl sulfide groups . A combination of azobenzene moieties and dynamic covalent bonds is also a prevalent strategy for the fabrication of light‐responsive LCP materials …”

“…Allyl sulfide functional groups are promising candidates to tackle recyclability and processing issues associated with chemically crosslinked LCP materials. Ji co‐workers demonstrated that light‐controlled exchange reaction between allyl sulfide groups allowed flexible processing of tubular actuators without the need of any assisting materials . LCEs were synthesized with allyl sulfide groups in the backbone.…”

“…It is typically difficult to attain reversible bending along with extension, contraction and expansion of the tube diameter, and controllable omnidirectional bending. Ji and co‐workers proposed a strategy to overcome these challenges by developing an LCE with dynamic allyl sulfide groups, which could be used to fabricate tether‐free soft tubular robots that exhibit complex locomotion . The same tube could have different locomotion in different regions and could be reprogrammed to have new locomotion modes again and again.…”

Photo-Actuation of Liquid Crystalline Elastomer Materials Doped with Visible Absorber Dyes under Quasi-Daylight

“…By depending on the structures and compositions, LCE materials can experience shape changes in response to specific external stimuli including magnetism [7,8], heat [9], electric field [10], light [11], ions [12], moisture [13,14], and solvent [15], etc. The outstanding stimuliresponsitivities enable them to be widely used in smart actuators [16][17][18][19][20][21], biomimetic devices [22][23][24][25], artificial organs [26][27][28], and microrobots [29][30][31], etc. Thermal stimuli and light stimuli play major roles in various applications of LCE materials [4,11].…”