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1. A Venus-flytrap-based actuator

   Volkov, Alexander ( February 2021 , Nature electronics)

   null (Ed.)

   Conformable electrodes can be used to manipulate the electrical properties of a Venus flytrap, creating actuators that can be wirelessly controlled. 

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2. Cellular shape micromachined actuator ribbons

   https://doi.org/10.1038/s41378-022-00421-y  

   Abbasalipour, Amin ; Palit, Prithviraj ; Sheikhlari, Sepehr ; Pakdelian, Siavash ; Pourkamali, Siavash ( August 2022 , Microsystems & Nanoengineering)

   This work presents a new class of micromachined electrostatic actuators capable of producing output force and displacement unprecedented for MEMS electrostatic actuators. The actuators feature submicron high aspect ratio transduction gaps lined up in two-dimensional arrays. Such an arrangement of microscale actuator cells allows the addition of force and displacements of a large number of cells (up to 7600 in one demonstrated array), leading to displacements ranging in the hundreds of microns and several gram forces of axial force. For 50 µm thick actuators with horizontal dimensions in the 1–4 millimeter range, an out-of-plane displacement of up to 678 µm at 46 V, a bending moment of up to 2.0 µNm, i.e., 0.08 N (~8 gram-force) of axial force over a 50 µm by 2 mm cross-sectional area of the actuator (800 kPa of electrostatically generated stress), and an energy density (mechanical work output per stroke per volume) up to 1.42 mJ/cm³was demonstrated for the actuators.

    

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3. Design of a Highly-Maneuverable Pneumatic Soft Actuator Driven by Intrinsic SMA Coils (PneuSMA Actuator)

   https://doi.org/10.1109/IROS45743.2020.9340803  

   Allen, Emily A. ; Swensen, John P. ( October 2020 , 2020 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS))

   This paper presents the design of a new soft pneumatic actuator whose direction and magnitude of bending may be precisely controlled via activation of different shape memory alloy (SMA) springs within the actuator, in conjunction with pneumatic actuation. This design is inspired by examples seen in nature such as the human tongue, where the combination of hydrostatic pressure and contraction of intrinsic muscle groups enables precise maneuverability and morphing capabilities. Here, SMA springs are embedded in the walls of the actuator, serving as intrinsic muscles that may be selectively activated to constrain the device. The pneumatic SMA (PneuSMA) actuator demonstrates remarkable spatial controllability evidenced by testing under different pressures and SMA activation combinations. A baseline finite element model is also developed to predict the actuator deformation under different pressure and activation conditions. 

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4. Multi-actuator light-controlled biological robots

   https://doi.org/10.1063/5.0091507  

   Wang, Jiaojiao ; Wang, Yueji ; Kim, Yongdeok ; Yu, Tianqi ; Bashir, Rashid ( September 2022 , APL Bioengineering)

   Biohybrid robots, composed of cellular actuators and synthetic scaffolds, have garnered much attention in recent years owing to the advantages provided by their biological components. In recent years, various forms of biohybrid robots have been developed that are capable of life-like movements, such as walking, swimming, and gripping. Specifically, for walking or crawling biorobots, there is a need for complex functionality and versatile and robust fabrication processes. Here, we designed and fabricated multi-actuator biohybrid walkers with multi-directional walking capabilities in response to noninvasive optical stimulation through a scalable modular biofabrication process. Our new fabrication approach provides a constant mechanical strain throughout the cellular differentiation and maturation process. This maximizes the myotube formation and alignment, limits passive bending, and produces higher active forces. These demonstrations of the new fabrication process and bioactuator designs can pave the way for advanced multi-cellular biohybrid robots and enhance our understanding of the emergent behaviors of these multi-cellular engineered living systems. 

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5. Strain-controlled Graphene-Polymer Angular Actuator

   https://doi.org/10.1557/adv.2019.276  

   Gilbert, S. Matt ; Molnar, Adam ; Horton-Bailey, Donez ; Yao, Helen Y. ; Zettl, Alex ( January 2019 , MRS Advances)

   ABSTRACT We demonstrate a suspended graphene-(poly(methyl methacrylate) (PMMA) polymer angular displacement actuator enabled by variable elastic modulus of the perforated stacked structure. Azimuthal flexures support a central disc-shaped membrane, and compression of the membrane can be used to control the rotation of the entire structure. Irradiating the PMMA on graphene stack with 5 kV electrons in a convention scanning electron microscope reduces the elastic modulus of the PMMA and allows graphene’s built in strain to dominate and compress the flexures, thus rotating the actuator. 

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