Photomorphogenesis of Diverse Autonomous Traveling Waves in a Monolithic Soft Artificial Muscle

Abstract

Biological organisms (e.g., batoid fish, etc.) possess the remarkable ability to morph their soft, sheet-like tissues into wavy morphologies and self-oscillate to make traveling waves, enabling myriad functionalities in propulsion, locomotion, and transportation. In contrast, current manmade soft robotic systems cannot adaptively make wavy morphologies and concurrently achieve wave propagation because the controllable actuation of desired 3D morphologies in entirely soft materials is a formidable challenge due to their continuously deformable bodies that own a large number of actuable degrees of freedom. Here, we report a bioinspired robotic system that not only allows photomorphogenesis of on-demand 3D wavy morphologies but also enables autonomous wave propagation in a monolithic soft artificial muscle (MSAM). This system employs a conceptually different design strategy based on a combination of two principles derived from plant morphogenesis and the undulatory motion of ray fish. The former offers a shaping principle based on differential growth that enables morphing MSAM into target wavy configurations, while the latter inspires a driving principle that induces autonomous propagation of shaped waves by rhythmic motor patterns. This waving system can be used as adaptive “soft engines/motors” that enable directional locomotion, intelligent transportation of cargo, and autonomous propulsion. It even produces programmable, complex artificial peristaltic waves. Our design allows controllable formation of 3D wavy morphologies and autonomous wave behaviors in the soft robotic system that would be useful for broad applications in adaptive, self-regulated mechanical systems for advanced robotics, soft machines, and energy harvest.

Self-Sustained Euler Buckling of an Optically Responsive Rod with Different Boundary Constraints

“…In recent years, various self-oscillating systems based on different stimuli-responsive materials have been constructed, such as thermally responsive polymer materials [ 14 ], hydrogels [ 15 , 16 ], ion gels [ 17 ], dielectric elastomer [ 18 ], liquid crystal elastomers (LCEs) [ 19 , 20 ], etc. Meanwhile, a variety of self-sustained motion modes have been proposed, such as rolling [ 4 , 7 , 21 ], bending [ 22 , 23 ], vibration [ 24 , 25 ], torsion [ 25 , 26 ], stretching and shrinking [ 27 , 28 ], spinning [ 29 ], swinging [ 30 ], buckling [ 31 , 32 , 33 , 34 ], jumping [ 35 , 36 , 37 ], rotation [ 38 ], snap-through [ 39 ], eversion or inversion [ 40 ], expansion and contraction [ 26 , 41 , 42 ], swimming [ 43 , 44 ], and even group behavior coupled by two asymmetric oscillators [ 45 ]. In order to compensate for the energy loss of self-sustained oscillation caused by damping dissipation, different self-feedback mechanisms have been proposed, such as self-shadowing mechanism [ 41 ], coupling mechanism among chemical diffusion, large deformation and chemical reaction [ 46 ], and multi process coupling mechanism among droplet evaporation, motion, and plate buckling [ 47 ].…”

“…As a classical mechanical instability phenomenon, the Euler buckling of a compression rod can be used as a new way to produce reliable self-sustained oscillation [ 55 ], and several experimental works on light-driven buckling of LCE have been reported in Refs. [ 31 , 32 , 33 ], recently. In this paper, we propose a new self-sustained Euler buckling LCE rod under steady illumination and investigate the effects of five typical boundary configurations on the oscillation.…”

Oscillating light engine realized by photothermal solvent evaporation

“…Recently, there have been a few successful advances in oscillating bending actuation under light irradiation 35 , 36 . A general strategy is to confine the incident light in a localized region (e.g., laser beam) so that the light-induced bending causes the actuator to be no longer illuminated by the light beam and bend back to be illuminated again 37 – 45 . This requires the incident light to have a very strict beam width and a special irradiation angle.…”

Self-Jumping of a Liquid Crystal Elastomer Balloon under Steady Illumination

“…In recent years, various self-oscillating systems based on diverse stimuli-responsive materials are reported, such as hydrogels [ 14 , 15 ], dielectric elastomers [ 16 ], ionic gels [ 17 ], liquid crystal elastomers (LCEs) [ 7 , 18 , 19 , 20 , 21 ], and thermally responsive polymer materials [ 22 ], etc. Furthermore, a variety of self-sustained motion modes have been constructed, such as bending [ 23 , 24 , 25 , 26 ], buckling [ 27 , 28 , 29 , 30 ], torsion [ 31 , 32 ], stretching and shrinking [ 33 , 34 ], rolling [ 35 , 36 ], swimming [ 9 ], swinging [ 37 , 38 ], vibration [ 39 , 40 , 41 ], jumping [ 42 , 43 , 44 ], rotation [ 45 ], eversion or inversion [ 46 , 47 ], and even synchronized motion of several coupled self-oscillators [ 48 ]. These self-sustained motions often originate from nonlinear feedback mechanisms including self-shadowing [ 3 , 27 , 28 ], coupling of liquid volatilization and membrane deformation [ 49 ], coupling mechanism among air expansion and liquid column movement [ 50 ], and coupling of plate buckling and chemical reaction [ 18 ].…”

“…Among various and effective stimuli in the LCE systems, light stimulus is more convenient to induce self-feedback to achieve self-sustained oscillation [ 43 ]. Recently, light-fueled self-oscillation based on LCE has attracted the attention of many scientists, and a large number of light-fueled self-oscillating systems based on LCE have been developed [ 30 , 43 , 44 , 59 , 60 ].…”