Variable stiffness morphing limb for amphibious legged robots inspired by chelonian environmental adaptations

Baines, Robert; Freeman, Simon E.; Fish, Frank E.; Kramer‐Bottiglio, Rebecca

doi:10.1088/1748-3190/ab68e8

Cited by 34 publications

(21 citation statements)

References 32 publications

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Section: Discussionmentioning

confidence: 99%

“…many state-of-the-art robots have been shown to expand their capabilities by gaining new locomotion modes, [28,75] avoiding obstacles, [30] or transitioning between body shapes suitable for swimming or walking. [77,78] Increased closed-loop control of morphology and material properties could eventually allow robots to rival the dynamic plasticity attained by natural systems. However, many open questions remain regarding when, how, and to what degree shape change is useful.…”

Section: Discussionmentioning

confidence: 99%

“…Baines et al recently demonstrated a life-size turtle-and tortoise-inspired morphing limb that could change between flipper and leg shapes, as a step toward amphibious robots which can accomplish both aquatic and terrestrial locomotion (Figure 3f). [77,78] The transformation from flipper to leg occurred via coupled variable stiffness and actuation materials distributed along the length of the morphing limb. Initially in a flipper shape, fluidic The quadrupedal robot shown here discovered that, after being damaged, it was more advantageous to change its shape than adapt its control policy.…”

Section: Shape Changing Robotsmentioning

confidence: 99%

Section: Shape Changing Robotsmentioning

confidence: 99%

“…For example, in the turtle-and tortoise-inspired morphing limb proposed by Baines et al, the robot could hold a flipper-like shape for hydrodynamically efficient swimming, and switch to a load-bearing leg-like shape for walking using a softening/stiffening thermoset epoxy (Figure 6c). [77,78] Stiffening could also allow a robot to lock in its shape and disengage its morphing actuators, to reduce energy requirements. Researchers have shown this concept in various applications, including using a variable stiffness conductive epoxy composite to selectively soften and stiffen a gripper to maintain the position of its payload without additional energy input or control loops.…”

Section: Shape Changingmentioning

confidence: 99%

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Shape Changing Robots: Bioinspiration, Simulation, and Physical Realization

et al. 2020

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are specialized for a single task, and cannot adapt their body to accomplish additional tasks after manufacture. Moreover, biological bodies are often highly regenerative, and able to repair and reconfigure their large-scale architecture in the face of significant damage or radical changes to their components. [3] For example, salamanders regenerate amputated limbs, [4] and fragments cut from arbitrary portions of planaria flatworms can rebuild (and rescale) their bodies to recover a full, correct anatomy. [3] Remarkably, many of these systems are able to retain information, such as learned memories, despite drastic reconfiguration or total replacement of their brains. [5] In these integrated living systems, intelligence, memory, learning, behavior, and body structure are all intertwined and emerge from the multiscale dynamics of the same robust and highly fault-tolerant medium.Evolution did not result in hard-coded body plans purely determined by genetic factors, but rather produced diverse examples of intelligent self-modifying systems which adapt to numerous extragenomic influences. [6] In this way, biology serves as an important proof-of-principle, and design challenge, for artificial intelligence and shape changing robots. Despite having access to this extensive set of model systems, the realization of general-purpose, adaptive robots has remained elusive. Researchers have proposed modular robots that can be attached to each other to expand functionality, [7] passively conforming universal grippers, [8] reconfigurable robotic skins, [9] self-assembling robot swarms, [10] gait-switching mechanisms [11] and controllers, [12,13] and algorithms that quickly re-adapt to multiple distinct tasks. [14] Such approaches succeed at adaptation but operate under the assumption that the robot's body is only reconfigured or reshaped due to external forces, and do not explore the possibility of synthetic machines that actively grow, regenerate, deform, or otherwise change the resting shape of their constituent components.With the introduction of a conformable gripper by Hirose in 1978, [15] followed by continuum robot arms, [16] silicone grippers, [17] and variable stiffness actuators, [18] robots that can adapt to real-world environments by changing their shape are becoming closer to reality. In particular, the idea of passively conforming around objects during grasping has been quite successful. [17,19,20] Soft robots have shown potential in other applications, including human-robot interaction and exploration, as reviewed by Kim et al., [21] Rus et al., [22] and others. [23,24] For a comprehensive review of the role of deformation in singlefunction soft robots, the reader is referred to Wang et al. [25] One of the key differentiators between biological and artificial systems is the dynamic plasticity of living tissues, enabling adaptation to different environmental conditions, tasks, or damage by reconfiguring physical structure and behavioral control policies. Lack of dynamic plasticity is a significant limitation for a...

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Shape Changing Robotsmentioning

confidence: 99%

Section: Shape Changing Robotsmentioning

confidence: 99%

Section: Shape Changingmentioning

confidence: 99%

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Shape Changing Robots: Bioinspiration, Simulation, and Physical Realization

et al. 2020

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Biohybrid Variable‐Stiffness Soft Actuators that Self‐Create Bone

et al. 2022

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temporarily deform during birth to enable the infant's head to pass through the narrow birth canal. After birth, this flexibility is no longer needed, but instead a rigid state is desired to protect the sensitive brain, and thus the material properties of the skull change, closing the skull into a rigid bone. Likewise, variable-stiffness components are of great interest to achieve morphing robotics and in bionics. [1,2] In medicine and tissue engineering, variable stiffness is also of fundamental importance, especially when interacting with the surrounding microenvironment. For instance, compliant hydrogels and scaffolds can be used to facilitate insertion and adaptation during surgery, and thereafter the transplanted materials harden to reconstruct the function and mechanical properties of the injured hard tissue. [2,3] A number of variable-stiffness actuators have been developed, but they mainly combine components with different stiffness and non-dynamic properties. [2,4] Novel functional materials are decisive for the development of new variable-stiffness systems and functionality. Bioinspired and biohybrid materials that integrate biological components [5] (e.g., cells, enzymes, phospholipids) would enable the development of unprecedented variable-stiffness systems and functionality.We here report a biohybrid variable-stiffness actuator that creates its own bone. The biohybrid actuator uses the electroactive polymer Polypyrrole (PPy) as the mechanically active component and is combined with alginate (Alg) hydrogels functionalized with cell-derived plasma membrane nanofragments (PMNFs) as the bioinducing source for mineralization and stiffening of the gel layer. This allows the development of unique soft-to-hard variable-stiffness actuators for potential applications in soft (micro-)robotics and bone tissue engineering (Figure 1). PMNFs were shown to be the nucleation sites for bone formation in vivo. [6] PMNFs comprise phospholipids and bone formation-related enzymes, including tissue non-specific alkaline phosphatase (TNALP), which promote the hydrolysis of phosphate-containing substrates and release free phosphate ions that further participate in the formation of calcium-phosphate minerals [e.g., amorphous calcium phosphate (ACP), hydroxyapatite (HAp)]. [7] Previous reports also demonstrated the ability of the PMNFs to promote rapid mineralization in vitro in just 2 to 3 days, [6,8] while live cells or recombinant TNALP require at least 2 to 3 weeks. [9] The PMNFs are assumed to maintain the membrane-bound enzymes and proteins Inspired by the dynamic process of initial bone development, in which a soft tissue turns into a solid load-bearing structure, the fabrication, optimization, and characterization of bioinduced variable-stiffness actuators that can morph in various shapes and change their properties from soft to rigid are hereby presented. Bilayer devices are prepared by combining the electromechanically active properties of polypyrrole with the compliant behavior of alginate gels that are uniquely ...

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Soft Actuators Made of Discrete Grains

et al. 2022

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microscale actuation. However, these material-based actuators are often slow or only expand or contract axially, preventing use in applications that require volumetric expansions. To address such limitations of existing actuating materials, actuators based on the liquid-to-gas phase change of solvent inclusions encapsulated in a hyperelastic matrix have been realized. Phasechange actuators are capable of inducing rapid volumetric expansion similar to fluidic actuators, without being tethered to an external fluid source. [29][30][31][32] Accepting the advantages of phasechange actuators, we now turn our attention to granular media. Granular assemblies, consisting of discrete grains, can be tuned to accomplish a variety of different responses. For example, favorable self-assembly of granular media can be achieved via modulating interparticle interactions and external stimuli, [33][34][35][36] and granular assemblies with different packing configurations have been shown to yield different bulk properties. [36][37][38][39] Furthermore, granular media can exhibit optimized changes in stiffness during jamming transitions, enabling tunable moduli. [16,[40][41][42][43][44] When unjammed, the bulk material is compliant, and when jammed, the bulk material can achieve the stiffness of the grains. Finally, when mixed into carrier fluids, granular media can impart thixotropic behavior on the carrier fluid due to dynamic jamming, [45][46][47][48] enabling 3D printing of previously unprintable materials. With all the advantageous properties granular media has to offer, the technology has seen application in soft robotics, [49][50][51][52] medical devices, [53][54][55] flexible airfoils, [56] and programmable aggregate architecture. [57] Here, we bring together the unique advantages of phasechange soft actuators and granular media to introduce soft granular actuators made of discrete, volumetrically expanding grains. A single active grain consists of multiple solvent cores encapsulated in a hyperelastic silicone shell (Ecoflex 00-30). At elevated temperatures, the encapsulated solvent vaporizes and increases the internal pressure of the hyperelastic shell, inducing volumetric expansion of the grain. The grains are independently capable of rapid, high-force microscopic actuation, and are also easily arranged into granular assemblies to form larger-scale bulk actuators. Furthermore, agglomerates of active grains can self-assemble from disordered arrangements to conform around objects and exhibit variable moduli. Finally, the use of grains suspended in a carrier solvent or resin enables compatibility with granular self-assembly and 3D printing techniques, offering the potential to print volumetrically expanding actuators into freeform patterns across scales.Recent work has demonstrated the potential of actuators consisting of bulk elastomers with phase-changing inclusions for generating high forces and large volumetric expansions. Simultaneously, granular assemblies have been shown to enable tunable properties via different packing...

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Variable stiffness morphing limb for amphibious legged robots inspired by chelonian environmental adaptations

Cited by 34 publications

References 32 publications

Shape Changing Robots: Bioinspiration, Simulation, and Physical Realization

Shape Changing Robots: Bioinspiration, Simulation, and Physical Realization

Biohybrid Variable‐Stiffness Soft Actuators that Self‐Create Bone

Soft Actuators Made of Discrete Grains

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