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1. Electromechanical Characterization of 3D Printable Conductive Elastomer for Soft Robotics

   https://doi.org/10.1109/RoboSoft48309.2020.9116027  

   Kim, Suhan ; Kim, Sukjun ; Majditehran, Houriyeh ; Patel, Dinesh K. ; Majidi, Carmel ; Bergbreiter, Sarah ( May 2020 , IEEE International Conference on Soft Robotics (RoboSoft))

   Soft, stretchable sensors, such as artificial skins or tactile sensors, are attractive for numerous soft robotic applications due to the low material compliance. Conductive polymers are a necessary component of many soft sensors, and this work presents the electromechanical characterization of 3D-printable conductive polymer composites. Dog-bone shaped samples were 3D printed using a digital light processing (DLP)-based 3D printer for characterization. The 3D printable resin consists of monomer, crosslinker, conductive nano-filler, and a photo-initiator. The characterization was performed in two tracks. First, the effect of two different crosslinkers was investigated with different compositions and second, the effect of concentration of conductive nano-fillers was explored. Crosslinkers were chosen by referring to previous studies, and carbon nanotubes (CNTs) were utilized as conductive nano-fillers. The samples were 3D printed and characterized using an electromechanical test setup. To demonstrate utility for 3D printed soft robotics, a capacitance-based joystick sensor composed of both conductive and non-conductive resins was 3D printed. 

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2. 3D Printed Gerotor Pump Geometries for Soft-Robot Actuation

   https://doi.org/10.1115/FPMC2023-111408  

   Gallentine, James ; Barth, Eric J. ( October 2023 , Proceedings of the ASMEBATH Symposium on Fluid Power and Motion Control)

   Often, fluidic soft robots are driven by large pneumatic or low-bandwidth hydraulic systems which struggle to meet performance objectives. This research presents the design of two morphologies of compact, positive displacement hydraulic pumps designed to act as power supplies for fluidic soft robots. These hydraulic pumps were designed to leverage additive manufacturing technology, creating cost-effective, yet volumetrically powerful units. The operational bandwidth of these pumps (> 10Hz) was substantially higher than the natural frequency of most elastomer-based soft robots (1–5Hz), allowing high control authority.

   These designs allow for highly scalable pumps, with performance documented in the paper. Due to the 3D printed nature of the pump components, manufacture cost is greatly reduced when compared to machined components. Each was tested driving various soft robotic actuators, demonstrating high-bandwidth, yet precise operation.

   With their minimal size, these pumps are candidates for un-tethered mobile soft robots, and their low weight and low noise allows them to be carried on the body for robotic actuators used in mobility rehabilitation.

    

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3. Printing Reconfigurable Bundles of Dielectric Elastomer Fibers

   https://doi.org/10.1002/adfm.202010643  

   Chortos, Alex ; Mao, Jie ; Mueller, Jochen ; Hajiesmaili, Ehsan ; Lewis, Jennifer A. ; Clarke, David R. ( March 2021 , Advanced Functional Materials)

   Active soft materials that change shape on demand are of interest for a myriad of applications, including soft robotics, biomedical devices, and adaptive systems. Despite recent advances, the ability to rapidly design and fabricate active matter in complex, reconfigurable layouts remains challenging. Here, the 3D printing of core‐sheath‐shell dielectric elastomer fibers (DEF) and fiber bundles with programmable actuation is reported. Complex shape morphing responses are achieved by printing individually addressable fibers within 3D architectures, including vertical coils and fiber bundles. These DEF devices exhibit resonance frequencies up to 700 Hz and lifetimes exceeding 2.6 million cycles. The multimaterial, multicore‐shell 3D printing method opens new avenues for creating active soft matter with fast programable actuation.

    

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4. Laser‐Induced Graphene for Electrothermally Controlled, Mechanically Guided, 3D Assembly and Human–Soft Actuators Interaction

   https://doi.org/10.1002/adma.201908475  

   Ling, Yun ; Pang, Wenbo ; Li, Xiaopeng ; Goswami, Shivam ; Xu, Zheng ; Stroman, David ; Liu, Yachao ; Fei, Qihui ; Xu, Yadong ; Zhao, Ganggang ; et al ( March 2020 , Advanced Materials)

   Mechanically guided, 3D assembly has attracted broad interests, owing to its compatibility with planar fabrication techniques and applicability to a diversity of geometries and length scales. Its further development requires the capability of on‐demand reversible shape reconfigurations, desirable for many emerging applications (e.g., responsive metamaterials, soft robotics). Here, the design, fabrication, and modeling of soft electrothermal actuators based on laser‐induced graphene (LIG) are reported and their applications in mechanically guided 3D assembly and human–soft actuators interaction are explored. Over 20 complex 3D architectures are fabricated, including reconfigurable structures that can reshape among three distinct geometries. Also, the structures capable of maintaining 3D shapes at room temperature without the need for any actuation are realized by fabricating LIG actuators at an elevated temperature. Finite element analysis can quantitatively capture key aspects that govern electrothermally controlled shape transformations, thereby providing a reliable tool for rapid design optimization. Furthermore, their applications are explored in human–soft actuators interaction, including elastic metamaterials with human gesture‐controlled bandgap behaviors and soft robotic fingers which can measure electrocardiogram from humans in an on‐demand fashion. Other demonstrations include artificial muscles, which can lift masses that are about 110 times of their weights and biomimetic frog tongues which can prey insects.

    

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5. 3D‐Printed Silicone Soft Architectures with Programmed Magneto‐Capillary Reconfiguration

   https://doi.org/10.1002/admt.201800528  

   Roh, Sangchul ; Okello, Lilian B. ; Golbasi, Nuran ; Hankwitz, Jameson P. ; Liu, Jessica A. ‐C. ; Tracy, Joseph B. ; Velev, Orlin D. ( January 2019 , Advanced Materials Technologies)

   Soft intelligent structures that are programmed to reshape and reconfigure under magnetic field can find applications such as in soft robotics and biomedical devices. Here, a new class of smart elastomeric architectures that undergo complex reconfiguration and shape change in applied magnetic fields, while floating on the surface of water, is reported. These magnetoactive soft actuators are fabricated by 3D printing with homocomposite silicone capillary ink. The ultrasoft actuators easily deform by the magnetic force exerted on carbonyl iron particles embedded in the silicone, as well as lateral capillary forces. The tensile and compressive moduli of the actuators are easily determined by their topological design through 3D printing. As a result, their responses can be engineered by the interplay of the intensity of the magnetic field gradient and the programmable moduli. 3D printing allows us to fabricate soft architectures with different actuation modes, such as isotropic/anisotropic contraction and multiple shape changes, as well as functional reconfiguration. Meshes that reconfigure in magnetic fields and respond to external stimuli by reshaping could serve as active tissue scaffolds for cell cultures and soft robots mimicking creatures that live on the surface of water.

    

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