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1. A dynamic electrically driven soft valve for control of soft hydraulic actuators

   https://doi.org/10.1073/pnas.2103198118  

   Xu, Siyi ; Chen, Yufeng ; Hyun, Nak-seung P. ; Becker, Kaitlyn P. ; Wood, Robert J. ( August 2021 , Proceedings of the National Academy of Sciences)

   null (Ed.)

   Regulation systems for fluid-driven soft robots predominantly consist of inflexible and bulky components. These rigid structures considerably limit the adaptability and mobility of these robots. Soft valves in various forms for fluidic actuators have been developed, primarily fluidically or electrically driven. However, fluidic soft valves require external pressure sources that limit robot locomotion. State-of-the-art electrostatic valves are unable to modulate pressure beyond 3.5 kPa with a sufficient flow rate (>6 mL⋅min −1 ). In this work, we present an electrically powered soft valve for hydraulic actuators with mesoscale channels based on a different class of ultrahigh-power density dynamic dielectric elastomer actuators. The dynamic dielectric elastomer actuators (DEAs) are actuated at 500 Hz or above. These DEAs generate 300% higher blocked force compared with the dynamic DEAs in previous works and their loaded power density reaches 290 W⋅kg −1 at operating conditions. The soft valves are developed with compact (7 mm tall) and lightweight (0.35 g) dynamic DEAs, and they allow effective control of up to 51 kPa of pressure and a 40 mL⋅min −1 flow rate with a response time less than 0.1 s. The valves can also tune flow rates based on their driving voltages. Using the DEA soft valves, we demonstrate control of hydraulic actuators of different volumes and achieve independent control of multiple actuators powered by a single pressure source. This compact and lightweight DEA valve is capable of unprecedented electrical control of hydraulic actuators, showing the potential for future onboard motion control of soft fluid-driven robots. 

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2. Inflatable Origami: Multimodal Deformation via Multistability

   https://doi.org/10.1002/adfm.202201891  

   Melancon, David ; Forte, Antonio Elia ; Kamp, Leon M. ; Gorissen, Benjamin ; Bertoldi, Katia ( June 2022 , Advanced Functional Materials)

   Inflatable structures have become essential components in the design of soft robots and deployable systems as they enable dramatic shape change from a single pressure inlet. This simplicity, however, often brings a strict limitation: unimodal deformation upon inflation. Here, multistability is embraced to design modular, inflatable structures that can switch between distinct deformation modes as a response to a single input signal. This system comprises bistable origami modules in which pressure is used to trigger a snap‐through transition between a state of deformation characterized by simple deployment to a state characterized by bending deformation. By assembling different modules and tuning their geometry to cause snapping at different pressure thresholds, structures capable of complex deformations that can be pre‐programmed and activated using only one pressure source are created. This approach puts forward multistability as a paradigm to eliminate a one‐to‐one relation between input signal and deformation mode in inflatable systems.

    

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3. Programmable soft valves for digital and analog control

   https://doi.org/10.1073/pnas.2205922119  

   Decker, Colter J. ; Jiang, Haihui Joy ; Nemitz, Markus P. ; Root, Samuel E. ; Rajappan, Anoop ; Alvarez, Jonathan T. ; Tracz, Jovanna ; Wille, Lukas ; Preston, Daniel J. ; Whitesides, George M. ( October 2022 , Proceedings of the National Academy of Sciences)

   In soft devices, complex actuation sequences and precise force control typically require hard electronic valves and microcontrollers. Existing designs for entirely soft pneumatic control systems are capable of either digital or analog operation, but not both, and are limited by speed of actuation, range of pressure, time required for fabrication, or loss of power through pull-down resistors. Using the nonlinear mechanics intrinsic to structures composed of soft materials—in this case, by leveraging membrane inversion and tube kinking—two modular soft components are developed: a piston actuator and a bistable pneumatic switch. These two components combine to create valves capable of analog pressure regulation, simplified digital logic, controlled oscillation, nonvolatile memory storage, linear actuation, and interfacing with human users in both digital and analog formats. Three demonstrations showcase the capabilities of systems constructed from these valves: 1) a wearable glove capable of analog control of a soft artificial robotic hand based on input from a human user’s fingers, 2) a human-controlled cushion matrix designed for use in medical care, and 3) an untethered robot which travels a distance dynamically programmed at the time of operation to retrieve an object. This work illustrates pathways for complementary digital and analog control of soft robots using a unified valve design. 

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4. A programmable epidermal microfluidic valving system for wearable biofluid management and contextual biomarker analysis

   https://doi.org/10.1038/s41467-020-18238-6  

   Lin, Haisong ; Tan, Jiawei ; Zhu, Jialun ; Lin, Shuyu ; Zhao, Yichao ; Yu, Wenzhuo ; Hojaiji, Hannaneh ; Wang, Bo ; Yang, Siyang ; Cheng, Xuanbing ; et al ( September 2020 , Nature Communications)

   Active biofluid management is central to the realization of wearable bioanalytical platforms that are poised to autonomously provide frequent, real-time, and accurate measures of biomarkers in epidermally-retrievable biofluids (e.g., sweat). Accordingly, here, a programmable epidermal microfluidic valving system is devised, which is capable of biofluid sampling, routing, and compartmentalization for biomarker analysis. At its core, the system is a network of individually-addressable microheater-controlled thermo-responsive hydrogel valves, augmented with a pressure regulation mechanism to accommodate pressure built-up, when interfacing sweat glands. The active biofluid control achieved by this system is harnessed to create unprecedented wearable bioanalytical capabilities at both the sensor level (decoupling the confounding influence of flow rate variability on sensor response) and the system level (facilitating context-based sensor selection/protection). Through integration with a wireless flexible printed circuit board and seamless bilateral communication with consumer electronics (e.g., smartwatch), contextually-relevant (scheduled/on-demand) on-body biomarker data acquisition/display was achieved.

    

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5. Fully 3D-printed soft robots with integrated fluidic circuitry

   https://doi.org/10.1126/sciadv.abe5257  

   Hubbard, Joshua D. ; Acevedo, Ruben ; Edwards, Kristen M. ; Alsharhan, Abdullah T. ; Wen, Ziteng ; Landry, Jennifer ; Wang, Kejin ; Schaffer, Saul ; Sochol, Ryan D. ( July 2021 , Science Advances)

   null (Ed.)

   The emergence of soft robots has presented new challenges associated with controlling the underlying fluidics of such systems. Here, we introduce a strategy for additively manufacturing unified soft robots comprising fully integrated fluidic circuitry in a single print run via PolyJet three-dimensional (3D) printing. We explore the efficacy of this approach for soft robots designed to leverage novel 3D fluidic circuit elements—e.g., fluidic diodes, “normally closed” transistors, and “normally open” transistors with geometrically tunable pressure-gain functionalities—to operate in response to fluidic analogs of conventional electronic signals, including constant-flow [“direct current (DC)”], “alternating current (AC)”–inspired, and preprogrammed aperiodic (“variable current”) input conditions. By enabling fully integrated soft robotic entities (composed of soft actuators, fluidic circuitry, and body features) to be rapidly disseminated, modified on demand, and 3D-printed in a single run, the presented design and additive manufacturing strategy offers unique promise to catalyze new classes of soft robots. 

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