Shape Memory Polymers with Patternable Recovery Onset Regulated by Light

Shape memory polymers (SMPs) show attractive prospects in emerging fields such as soft robots and biomedical devices. Although their typical trigger-responsive character offers the essential shape-changing controllability, having to access external stimulation is a major bottleneck toward many applications. Recently emerged autonomous SMPs exhibit unique stimuli-free shape-shifting behavior with its controllability achieved via a delayed and programmable recovery onset. Achieving multi-shape morphing in an arbitrary fashion, however, is infeasible. In this work, a molecular design that allows to spatio-temporally define the recovery onset of an autonomous shape memory hydrogel (SMH) is reported. By introducing nitrocinnamate groups onto an SMH, its crosslinking density can be adjusted by light. This affects greatly the phase separation kinetics, which is the basis for the autonomous shape memory behavior. Consequently, the recovery onset can be regulated between 0 to 85 min. With masked light, multiple recovery onsets in an arbitrarily defined pattern which correspondingly enable multi-shape morphing can be realized. This ability to achieve highly sophisticated morphing without relying on any external stimulation greatly extends the versatility of SMPs.

Hierarchical network relaxation of a dynamic cross-linked polyolefin elastomer for advanced reversible shape memory effect

Reversible shape-memory polymers (RSMPs) are highly desired for soft actuators due to the repeatability of deformation. Herein, a polyolefin elastomer vitrimer (POEV) was prepared by constructing a dynamic cross-linked network based on boronic ester bonds. POEV showed varied network relaxation in a wide temperature range due to hierarchical network relaxation, and then the entropy decreased and the relaxation of POEV chains was facilely controlled by temperature. The controllable relaxation of POEV by programming the temperature enabled the actuation domain with a reduction in entropy and the skeleton domain with a relatively high entropy can be built in POEV, greatly affecting the reversible shape memory effects (RSMEs). The topological rearrangement resulted from the activated exchange of dynamic covalent bonds, which enables POEV with good shape reconfigurability, and allows for complicated 3D shapes and shape-shifting on demand. More interestingly, combining the decreasing entropy of POEV chains and fully topological rearrangement tailored by temperature, hybrid aligned carbon nanotubes (CNTs) can be constructed in POEV via a two-stage training. Then, the aligned CNTs can enhance the elasticity and act as a hybrid skeleton for RSMEs, avoiding the negative impact of CNTs on the reversible actuation strain. The hierarchical network relaxation facilitates combining all these unusual properties in one shape memory network synergistically, paving new avenues for realizing smart materials with advanced RSME.

Localized Photoactuation of Polymer Pens for Nanolithography

Localized actuation is an important goal of nanotechnology broadly impacting applications such as programmable materials, soft robotics, and nanolithography. Despite significant recent advances, actuation with high temporal and spatial resolution remains challenging to achieve. Herein, we demonstrate strongly localized photoactuation of polymer pens made of polydimethylsiloxane (PDMS) and surface-functionalized short carbon nanotubes based on a fundamental understanding of the nanocomposite chemistry and device innovations in directing intense light with digital micromirrors to microscale domains. We show that local illumination can drive a small group of pens (3 × 3 over 170 μm × 170 μm) within a massively two-dimensional array to attain an out-of-plane motion by more than 7 μm for active molecular printing. The observed effect marks a striking three-order-of-magnitude improvement over the state of the art and suggests new opportunities for active actuation.

Self-Sensing Actuators Based on a Stiffness Variable Reversible Shape Memory Polymer Enabled by a Phase Change Material

Soft actuators with integrated mechanical and actuation properties and self-sensing ability are still a challenge. Herein, a stiffness variable polyolefin elastomer (POE) with a reversible shape memory effect is prepared by introducing a typical phase change material, i.e., paraffin wax (PW). It is found that the variable stiffness of POE induced by PW can balance the reversible strain and load-bearing capability of actuators. Especially, carbon nanotubes (CNTs) are concentrated in a thin surface layer by spraying and hot pressing in the soft state of POE/PW blends, providing signal transductions for the strain and temperature perception for actuators. Taking advantage of tunable reversible deformation and mechanical transformation of the POE/PW actuator, different biomimetic robotics, including grippers with high load-bearing capability (weight-lifting ratio > 146), walking robots that can sense angles of joints, and high-temperature warning robots are demonstrated. A scheme combining the variable stiffness and electrical properties provides a versatile strategy to integrate actuation performance and self-sensing ability, inspiring the development of multifunctional composite designs for soft robotics.

Janus Photochemical/Photothermal Azobenzene Inverse Opal Actuator with Shape Self-Recovery toward Sophisticated Motion

Azobenzene actuators have aroused enormous research interest due to their excellent performance and promising applications in the fields of soft robots, artificial muscles, etc. However, there are still challenges for the fabrication of azobenzene actuators with a sophisticated actuation mode owing to the unitary actuation direction and slow thermal relaxation of cis- to trans-azobenzene mesogens. To solve these problems, this paper presents a facile fabrication method of a Janus azobenzene inverse opal actuator with one side made of the monodomain azobenzene polymer and the other side made of the polydomain azobenzene inverse opal structure. Gradient-layer spacing structure of the film in its cross section is proven by synchrotron small-angle X-ray diffraction. The introduction of the inverse opal structure mainly provides a polydomain mesogen alignment, large specific surface area, low elastic modulus, and structure color. The synergetic actuation of the photochemical/photothermal mode produces multiple actuation directions, a larger actuation force, and an alteration of the structure color. Shape self-recovery of this Janus azobenzene actuator contributes to some promising applications, such as crawling on a smooth surface, driving an engine axis, and logic electric circuit for the coding technique. This work is of great significance for the design and fabrication of novel-type photoactuators.

Optically Reconfigurable Shape Memory Metallo-Polymer Mediated by Carbolong Complex and Radically Exchangeable Covalent Bond

Conventional shape memory polymers (SMPs) are restricted to predetermined permanent shape, therefore cannot be remoulded arbitrarily to adapt to variant application scenarios. Meanwhile, shape memory behaviour is mostly thermally active...

Laser Actuated Microgripper Using Optimized Chevron-Shaped Actuator

In this paper, we propose a laser actuated microgripper that can be activated remotely for micromanipulation applications. The gripper is based on an optothermally actuated polymeric chevron-shaped structure coated with optimized metallic layers to enhance its optical absorbance. Gold is used as a metallic layer due to its good absorption of visible light. The thermal deformation of the chevron-shaped actuator with metallic layers is first modeled to identify the parameters affecting its behavior. Then, an optimal thickness of the metallic layers that allows the largest possible deformation is obtained and compared with simulation results. Next, microgrippers are fabricated using conventional photolithography and metal deposition techniques for further characterization. The experiments show that the microgripper can realize an opening of 40 µm, a response time of 60 ms, and a generated force in the order of hundreds of µN. Finally, a pick-and-place experiment of 120 µm microbeads is conducted to confirm the performance of the microgripper. The remote actuation and the simple fabrication and actuation of the proposed microgripper makes it a highly promising candidate to be utilized as a mobile microrobot for lab-on-chip applications.

Low-Voltage Actuator with Bilayer Structure for Various Biomimetic Locomotions

Composites based on a shape-memory polymer doped with conductive particles are considered as soft actuators for artificial muscles and robots. Low-voltage actuating is expected to reduce equipment requirement and safety hazards, which requires a highly conductive particle content but weakens the reversible deformation. The spatial distribution of the conductive particle is key to decreasing the actuating voltage and maintaining the reversible deformation. Herein, an approach of fabricating a low-voltage actuator that can perform various biomimetic locomotions by spraying and hot pressing is reported. Carbon nanotubes (CNTs) are enriched inside the surface layer of poly(ethylene-co-vinyl acetate) (EVA) to form a high-density conductive network without degradation of the reversible deformation. The bilayer CNT/EVA actuator exhibits a reversible transformation of more than 10% even with 100 cycles, which requires an applied voltage of just 15 V. Taking advantage of the reprogrammability of the CNT/EVA actuator and reversible shift between the different shapes, different biomimetic locomotions (sample actuator, gripper, and walking robot) are demonstrated without any additional mechanical components. A scheme combining the electrical properties and the shape-memory effect provides a versatile strategy to fabricate low-voltage-actuated polymeric actuators, providing inspiration in the development of electrical soft actuators and biomimetic devices.

Stimuli-responsive surfaces for switchable wettability and adhesion

Diverse unique surfaces exist in nature, e.g. lotus leaf, rose petal and rice leaf. They show similar contact angles but different adhesion properties. According to the different wettability and adhesion characteristics, this review reclassifies different contact states of droplets on surfaces. Inspired by the biological surfaces, smart artificial surfaces have been developed which respond to external stimuli and consequently switch between different states. Responsive surfaces driven by various stimuli, e.g. stretching, magnetic, photo, electric, temperature, humidity and pH, are discussed. Studies reporting on either atmospheric or underwater environments are discussed. The application of tailoring surface wettability and adhesion includes microfluidics/droplet manipulation, liquid transport and harvesting, water energy harvesting and flexible smart devices. Particular attention is placed on the horizontal comparison of smart surfaces with the same stimuli. Finally, the current challenges and future prospects in this field are also identified.

Design of Stretchable Holey Gold Biosensing Electrode for Real-Time Cell Monitoring

In bioelectronics, gold thin films have been widely used as sensing electrodes for probing biological events due to their high conductivity, chemical inertness, biocompatibility, wide electrochemical window, and facile surface modification. However, they are intrinsically not stretchable, which limits their applications in detecting biological reactions when a soft biological system is mechanically deformed. Here, we report on a nanosphere lithography-based strategy to generate ordered microhole gold thin-film electrodes supported by elastomeric substrates. Both experimental and theoretical studies show that the presence of microholes substantially suppresses the catastrophic crack propagation-the main reason for electrical failure for a continuous gold film. As a result, the holey gold film achieves a ∼94% stretchable limit, after which the conductivity is lost, in contrast to ∼4% for the nonstructured counterpart. Furthermore, the pinhole gold electrode is successfully used to monitor the H₂O₂ released from living cells under dynamic stretching conditions.

Self-Healing and Reconfigurable Actuators Based on Synergistically Cross-Linked Supramolecular Elastomer

Stimulus-responsive soft actuators show great potential in intelligent robot systems for their various virtues, such as arbitrary shape morphing, outstanding adaptability to environment, and multidegrees of freedom. However, it is extremely challenging to achieve a combination of excellent actuating performance and robust mechanical strength as well as self-healing property. Herein we report a near-infrared light-responsive soft actuator based on the synergistic effects of a crystalline physical cross-linked network and a hydrogen bonding supramolecular network. The actuator exhibits outstanding comprehensive performance including fast and reliable light-responsive behavior (bending angle over 90° within 1.6 s), robust mechanical strength (12.52 MPa), superfast self-healing speed (2 s), and satisfactory self-healing efficiency in both mechanical (87.68%) and actuating (99.50%) performance. In addition, it is convenient to fabricate and reconfigure the actuators by a mild-temperature molding strategy to acquire various three-dimensional structures, thus achieving diverse actuating locomotion. This work provides a powerful and facile strategy to prepare soft actuators with intriguing performance, allowing significant progress in broadening their practical application.

New Morphogenetic Strategy Inspired by the Viscoelasticity of Polymers

A new morphogenetic strategy was developed to realize continuously modulated and reprogrammable three-dimensional shape transitions by fully exploring the potential of macromolecular conformational modulations. Geometric information was defined in the planar shape memory polymeric sheets through the application of spatially differentiated thermo-temporal conditions in the shape memory creation stage. Due to the viscoelasticity of polymers, nonuniform inner stress distribution was encoded in spite of the homogeneous composition, which was released under the activation of uniform heating. Compared to the traditional shape-programming strategies, the present research offered the opportunity to generate physical patterns by modulating the thermal histories of polymers. It brought the advantages of a continuously regulated degree of discrepancy between different regions, which enabled fine-tuning of the targeted three-dimensional (3D) shape. In addition, suitable annealing treatment could lead to the elimination of thermal history. That is, the geometric information could be erased and re-encoded, making unlimited diverse 3D structures from the same piece of polymer a reality.

Reversible Actuation via Photoisomerization-Induced Melting of a Semicrystalline Poly(Azobenzene)

Photoisomerization of azobenzene in polymer matrices is a powerful method to convert photon energy into mechanical work. While most previous studies have focused on incorporating azobenzene within amorphous or liquid crystalline materials, the limited extents of molecular ordering and correspondingly modest enthalpy changes upon switching in such systems has limited the achievable energy densities. In this work, we introduce a semicrystalline main-chain poly(azobenzene), where photoisomerization is capable of reversibly triggering melting and recrystallization under essentially isothermal conditions. These materials can be drawn into aligned fibers, yielding optically driven two-way shape memory actuators capable of reversible bending.

Transparent photoactuators based on localized-surface-plasmon-resonant semiconductor nanocrystals: a platform for camouflage soft robots

Among the various kinds of actuators, photoactuators with the advantages of wireless and remote manipulation have attracted the interest of many researchers. However, it is challenging to develop transparent photoactuators for camouflage soft robots, because most of the current photoactuators use colored or even black light-absorbing agents. Here, we fabricate a series of transparent actuators by employing localized-surface-plasmon-resonant semiconductor nanocrystals, which mainly respond to infrared light. In this way, we introduce the advantages of wireless and remote manipulation into the camouflage soft robots. Three semiconductor nanocrystals (In2O3:Sn, W18O49 and CuS nanocrystals) are fabricated as the photothermal conversion agents to construct the photoactuators. Owing to the weak absorption of visible light, the fabricated actuators exhibit high transparency (maximum transmittance >72% at 600 nm). Meanwhile, they demonstrate remarkable deformations upon near infrared light irradiation (bending curvature up to 0.66 cm-1). Finally, a worm-like crawling robot, a glasswing butterfly robot and a two-finger robot hand are constructed to demonstrate the ability of remote manipulation and inconspicuousness in both the robot appearance and the driving signal, attaining excellent passive camouflage function. These results provide a promising platform for remote-controlled camouflage soft robots and biomimic applications, which will be of significance in the field of soft robotics.

Remotely Light-Powered Soft Fluidic Actuators Based on Plasmonic-Driven Phase Transitions in Elastic Constraint

Materials capable of actuation through remote stimuli are crucial for untethering soft robotic systems from hardware for powering and control. Fluidic actuation is one of the most applied and versatile actuation strategies in soft robotics. Here, the first macroscale soft fluidic actuator is derived that operates remotely powered and controlled by light through a plasmonically induced phase transition in an elastomeric constraint. A multiphase assembly of a liquid layer of concentrated gold nanoparticles in a silicone or styrene-ethylene-butylene-styrene elastic pocket forms the actuator. Upon laser excitation, the nanoparticles convert light of specific wavelength into heat and initiate a liquid-to-gas phase transition. The related pressure increase inflates the elastomers in response to laser wavelength, intensity, direction, and on-off pulses. During laser-off periods, heating halts and condensation of the gas phase renders the actuation reversible. The versatile multiphase materials actuate-like soft "steam engines"-a variety of soft robotic structures (soft valve, pnue-net structure, crawling robot, pump) and are capable of operating in different environments (air, water, biological tissue) in a single configuration. Tailored toward the near-infrared window of biological tissue, the structures actuate also through animal tissue for potential medical soft robotic applications.

Matching Magnetic Heating and Thermal Actuation for Sequential Coupling in Hybrid Composites by Design

Sequentially coupling two material functions requires matching the output from the first with the input of the second function. Here, magnetic heating controls thermal actuation of a hybrid composite in a challenging system environment causing an elevated level of heat loss. The concept is a hierarchical design consisting of an inner actuator of nanocomposite material, which can be remotely heated by exposure to an alternating magnetic field (AMF) and outer layers of a porous composite system with a closed pore morphology. These porous layers act as heat insulators and as barriers to the surrounding water. By exposure to the AMF, a local bulk temperature of 71 °C enables the magnetic actuation of the device, while the temperature of the surrounding water is kept below 50 °C. Interestingly, the heat loss during magnetic heating leads to an increase of the water phase (small volume) temperature. The temperature increase is able to sequentially trigger an adjacent thermal actuator attached to the actuator composite. In this way it could be demonstrated how the AMF is able to initiate two kinds of independent actuations, which might be interesting for robotics operating in aqueous environments.

Visible and infrared three-wavelength modulated multi-directional actuators

In recent years, light-guided robotic soft actuators have attracted intense scientific attention and rapidly developed, although it still remains challenging to precisely and reversibly modulate the moving directions and shape morphing modes of soft actuators with ease of stimulating operation. Here we report a strategy of building a multi-stimuli-responsive liquid crystal elastomer soft actuator system capable of performing not only multi-directional movement, but also different shape morphing modes. This strategy is based on the selective stimulation of specific domains of the hierarchical structured actuator through the modulation of three wavelength bands (520, 808, 980 nm) of light stimulus, which release the actuation system from light scanning position/direction restriction. Three near-infrared dual-wavelength modulated actuators and one visible/infrared tri-wavelength modulated multi-directional walker robot are demonstrated in this work. These devices have broad application prospects in robotic and biomimetic technology.

Design of Ethylene-Vinyl Acetate Copolymer Fiber with Two-Way Shape Memory Effect

One-dimensional shape memory polymer fibers (SMPFs) have obvious advantages in mechanical properties, dispersion properties, and weavability. In this work, a method for fabricating semi-crystallization ethylene-vinyl acetate copolymer (EVA) fiber with two-way shape memory effect by melt spinning and ultraviolet (UV) curing was developed. Here, the effect of crosslink density on its performance was systematically analyzed by gel fraction measurement, tensile tests, DSC, and TMA analysis. The results showed that the crosslink density and shape memory properties of EVA fiber could be facilely adjusted by controlling UV curing time. The resulting EVA fiber with cylindrical structure had a diameter of 261.86 ± 13.07 μm, and its mechanical strength and elongation at break were 64.46 MPa and 114.33%, respectively. The critical impact of the crosslink density and applied constant stress on the two-way shape memory effect were analyzed. Moreover, the single EVA fiber could lift more than 143 times its own weight and achieve 9% reversible actuation strain. The reversible actuation capability was significantly enhanced by a simple winding design of the single EVA fiber, which provided great potential applications in smart textiles, flexible actuators, and artificial muscles.

Electro and Light-Active Actuators Based on Reversible Shape-Memory Polymer Composites with Segregated Conductive Networks

Reversible shape-memory polymers (RSMPs) show great potential in actuating applications because of its repeatability among many other advantages. Indeed, in many cases, multiresponsive RSMPs are more expected, and the strategy to introduce functional fillers without deteriorating the reversible deformation performance is of great importance. Here, a facile strategy to balance the electro, photothermal performance, and molecular chain mobility is reported. Segregated conductive networks of carbon nanotubes (S-CNTs) are constructed in the poly(ethylene-co-octene) (POE) matrix at a relatively low filler loading, which renders the composite good electrical, photothermal, and actuating properties. A low percolation threshold of 0.25 vol % is achieved. The electrical conductivity is up to 0.046 S·cm^-1 for the POE/S-CNT composites with 2 vol % CNT, and the absorption of light (760 nm) is above 90%. These characteristics guarantee that the actuator can be driven at low voltage (≤36 V) and suitable light intensity (250 mW·cm^-2) with a good actuating performance. An electric gripper and a light-active crawling robot demonstrate the potential applications in multiresponsive robots. This work introduces a facile strategy to fabricate multiresponsive RSMPs by designing CNT network structures in polymer composites and holds great potential to enlarge the applications of RSMPs in many areas including artificial muscles and bionic robots.

Precise Self-Assembly and Controlled Catalysis of Thermoresponsive Core-Satellite Multicomponent Hybrid Nanoparticles

The construction of multicomponent hybrid nanomaterials with well-controlled architecture, especially bearing an ordered homogeneity and distribution of the subunits with tunable functions, is a key challenge in chemistry and material science. Herein, we reported a versatile and novel strategy to fabricate core-satellite multicomponent nanostructures with tunable interparticle distances and catalysis properties by the combination of surface-initiated reversible addition-fragmentation chain transfer (SI-RAFT) polymerization and self-assembly. The arrangement and interparticle distance of gold satellites could be precisely tuned by the SI-RAFT polymerization process and the feeding ratio of gold nanoparticles (AuNPs) and the core nanoparticle. It is worth to note that multilayered core-satellite nanostructures have been fabricated by a high-feeding ratio of AuNPs and magnetite NP (MNP)@SiO₂-PNIPAm. Notably, the core-satellite MNP@SiO₂-PNIPAm-Au nanoparticles exhibited excellent thermoresponsive behaviors with the change of temperature. Furthermore, the catalytic efficiency of MNP@SiO₂-PNIPAm-Au nanoparticles via the reduction of 4-nitrophenol to 4-aminophenol can be well modulated by the nanoparticle size, temperature, and polymer feed ratio. This strategy for precise construction of core-satellite nanostructures would open a new pathway to construct multicomponent functional nanostructures.

A shape-shifting composite hydrogel sheet with spatially patterned plasmonic nanoparticles

A simple and reliable approach was developed to fabricate thermo-responsive composite hydrogel sheets with spatially patterned regions of plasmonic gold nanoparticles. The same hydrogel exhibited different modes of shape deformation under near-infrared laser irradiation depending on the irradiation direction.

Dual-Programmable Shape-Morphing and Self-Healing Organohydrogels Through Orthogonal Supramolecular Heteronetworks

Programmable materials that can change their inherent shapes or properties are highly desirable due to their promising applications. However, among various programmable shape-morphing materials, the single control route allows temporary states to recover the unchangeable former state, thus lacking the sophisticated programmability for their shape-encoding behaviors and mechanics. Herein, dual-programmable shape-morphing organohydrogels featuring supramolecular heteronetworks are developed. In the system, the metallo-supramolecular hydrogel framework and micro-organogels featuring semicrystalline comb-type networks independently respond to different stimuli, thereby providing orthogonal dual-switching mechanics and ultrahigh mechanical strength. The supramolecular heteronetworks also possess excellent self-healing properties. More notably, such orthogonal supramolecular heteronetworks demonstrate hierarchical shape morphing performance that far exceeds conventional shape-morphing materials. Utilizing this dual programming strategy of the orthogonal supramolecular heteronetworks, the material's permanent shape can be manipulated in a step-wise shape morphing process, thereby realizing sophisticated shape changes with a high degree of freedom. The organohydrogels can act as a biomimetic smart device for the on-demand control of unidirectional liquid transport. Based on these characteristics, it is anticipated that the supramolecular organohydrogels may serve as adaptive programmable materials for a variety of applications.

2D-to-3D Shape Transformation of Room-Temperature-Programmable Shape-Memory Polymers through Selective Suppression of Strain Relaxation

Although shape-memory polymers (SMPs) can alter their shapes upon stimulation of environmental signals, complex shape transformations are usually realized by using advanced processing technologies (four-dimensional printing) and complicated polymer structure design or localized activation. Herein, we demonstrate that stepwise controlled complex shape transformations can be obtained from a single flat piece of SMP upon uniform heating. The shape-memory blends prepared by solution casting of poly(ethylene oxide) and poly(acrylic acid) (PAA) exhibit excellent mechanical and room-temperature shape-memory behaviors, with fracture strain beyond 800% and both shape memory and shape recovery ratio higher than 90%. After plastic deformation by stretching under ambient conditions, the material is surface-patterned to induce the formation of an Fe³⁺-coordinated PAA network with gradually altered cross-linking density along the thickness direction at desired areas. Upon subsequent heating for shape recovery, strain release is restricted by the PAA network to different extents depending on the cross-linking density, which results in bending deformation toward the nonpatterned side and leads to three-dimensional shape transformation of the SMP. More interestingly, by sequentially dissociating the PAA network via UV or visible light-induced photoreduction of Fe³⁺ to Fe²⁺, residual strains can be removed in a spatially controlled manner. Using this approach, a series of origami shapes are obtained from a single SMP with a tailored two-dimensional initial shape. We also demonstrate that by incorporating polydopamine nanoparticles as photothermal fillers into the material, the whole shape transformation process can be carried out at room temperature by using near-infrared light.

A Rewritable, Reprogrammable, Dual Light-Responsive Polymer Actuator

We report on the fabrication of a rewritable and reprogrammable dual-photoresponsive liquid crystalline-based actuator containing an azomerocyanine dye that can be locally converted into the hydroxyazopyridinium form by acid treatment. Each dye absorbs at a different wavelength giving access to programmable actuators, the folding of which can be controlled by using different colors of light. The acidic patterning is reversible and allows the erasing and rewriting of patterns in the polymer film, giving access to reusable, adjustable soft actuators.

A new function for thermal phase transition-based polymer actuators: autonomous motion on a surface of constant temperature

It is very challenging to make materials capable of autonomous oscillation known in many living systems (such as the heartbeat). Herein, we describe an approach to creating a thermo-mechano-thermal feedback loop for thermal phase transition-based polymer actuators, which leads to hour-long, autonomous motion on a substrate surface of constant temperature. We investigated the variables that determine the amplitude and period of the motion, and demonstrated exemplary physical work powered by direct thermomechanical energy conversion. Such continuous motion of a solid polymer driven by thermal energy without the need for temperature up/down switching is unprecedented, and the validated feedback loop can be implemented into other thermal phase transition-based polymer actuators.