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. 2021 Jul 14;7(29):eabe5257.
doi: 10.1126/sciadv.abe5257. Print 2021 Jul.

Fully 3D-printed soft robots with integrated fluidic circuitry

Joshua D Hubbard  1   2   3 , Ruben Acevedo  2   3 , Kristen M Edwards  2   3   4 , Abdullah T Alsharhan  2 , Ziteng Wen  2   3 , Jennifer Landry  2   3 , Kejin Wang  2 , Saul Schaffer  2   3   5 , Ryan D Sochol  6   3   7   8
Affiliations

Fully 3D-printed soft robots with integrated fluidic circuitry

Joshua D Hubbard et al. Sci Adv. .

Abstract

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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Figures

Fig. 1
Fig. 1. Design and additive manufacturing strategy for PolyJet 3D printing unified soft robotic systems comprising fully integrated fluidic circuitry in a single print run.
(A) Modular 3D CAD models and analogous electronic circuit symbols of fluidic circuit elements, fluidic interconnects, soft actuators, and structural casing. (B) CAD model and corresponding analogous circuit diagram of a unified soft robot with a fully integrated fluidic oscillator circuit. (C) Conceptual illustration of multimaterial PolyJet 3D printing the soft robot using compliant (black), rigid (white), and water-soluble support (yellow) materials. (D) Sequential time-lapse images of the PolyJet 3D printing process. Scale bar, 5 cm; see also movie S1. (E and F) Fabrication results for the unified multimaterial soft robot with integrated fluidic circuitry (E) before and (F) after support material removal. Scale bars, 2 cm. Photo credits: Ruben Acevedo, University of Maryland College Park.
Fig. 2
Fig. 2. Operating principles and results for PolyJet 3D printing–based fluidic circuit elements comprising integrated compliant (black) and rigid (white) materials.
(A to C) Conceptual illustrations of the (A) architecture, (B) “forward flow” state, and (C) “reverse flow” state for the fluidic diode. (D) Experimental results for directional fluid flow versus pressure for the fluidic diode. (E to H) Conceptual illustrations of the (E) architecture, (F) “closed” state [induced by a source pressure (PS) input], (G) “open” state [facilitated by a gate pressure (PG) input of sufficient magnitude], and (H) “reclosed” state (caused by a high PG input) for the normally closed fluidic transistor. The reclosed state dynamics can be adjusted by tuning the post height (HP). (I to K) Experimental results for source-to-drain fluid flow (QSD) versus PG corresponding to distinct, constant PS inputs for normally closed fluidic transistors designed with HP = (I) 0 μm, (J) 250 μm, and (K) 500 μm. (L to N) Conceptual illustrations of the (L) architecture, (M) open state, and (N) closed state (facilitated by a PG input of sufficient magnitude) for a normally open fluidic transistor. (O to R) Simulations of diaphragm displacement for fluidic transistors with diaphragm area ratios of (left) 1 (γ1), (middle) 2 (γ2), and (right) 3.5 (γ3) for PG = (O) 0 kPa, (P) 13 kPa, (Q) 23 kPa, and (R) 54 kPa. See also movie S2. (S) Experimental results for relative QSD versus PG for normally open fluidic transistors with varying γ (PS = 20 kPa) (see also fig. S1). All error bands denote SD.
Fig. 3
Fig. 3. Operating principle and experimental results for a constant flow–based soft robotic turtle.
(A to F) Conceptual illustrations of the soft robot, the integrated fluidic oscillator circuit, and analogous circuit diagrams corresponding to the six primary states based on constant-flow input conditions. (G) Experimental results for soft robot functionality under constant-flow conditions (10 ml/min) during a representative operational period. Scale bar, 3 cm; see also movie S3. Photo credits: Ruben Acevedo, University of Maryland College Park. (H) Quantified experimental results for normalized vertical deformation of each soft actuating limb versus time under constant-flow conditions (10 ml/min). Blue, left limb; red, right limb. a.u., arbitrary unit.
Fig. 4
Fig. 4. Operating principle and experimental results for a sinusoidal input–based soft robotic turtle.
(A to D) Conceptual illustrations and analogous circuit diagrams of the four primary states based on sinusoidal PG input conditions and a constant PS input. The integrated normally open fluidic transistors include distinct γ properties (γ1 < γ2 < γ3). (E) Fabrication results. Scale bar, 2 cm. Photo credits: Ruben Acevedo, University of Maryland College Park. (F) Experimental results for soft actuator–associated flipper displacements corresponding to a constant PS input of 40 kPa and varying PG input. (G) DIC-processed experimental results of the flipper displacement path under a constant PS input of 60 kPa and a sinusoidal PG input that oscillated from 0 to 80 kPa with a frequency of 0.1 Hz. Blue and red denote inflation- and deflation-associated displacement cycles, respectively.
Fig. 5
Fig. 5. Concepts and results for a preprogrammed, aperiodic fluidic input–based soft robotic hand with integrated fluidic circuitry.
(A to D) Conceptual illustrations and analogous circuit diagrams of the four primary states based on distinct PG magnitudes, while a PS input remains constant. The integrated normally open fluidic transistors include distinct γ properties (γ1 < γ2 < γ3). (E and F) Experimental results for a soft robotic finger with an integrated γ3 fluidic transistor for PS = 20 kPa and PG = (E) 0 kPa and (F) 20 kPa. Scale bars, 2 cm; see also movie S4. Photo credits: Kristen M. Edwards, Jennifer Landry, and Ryan D. Sochol, University of Maryland College Park. (G) Quantified experimental results for fingertip actuation force versus PG for soft robotic finger–fluidic transistor systems with varying γ and PS of 10 kPa. Error bands denote SD. (H) Sequential time-lapse images of the PolyJet 3D printing process. Scale bar, 2 cm; see also movie S5. Photo credit: Joshua D. Hubbard, University of Maryland, College Park. (I) Fabrication results. Scale bar, 2 cm. Photo credit: Joshua D. Hubbard and Kristen M. Edwards, University of Maryland, College Park. (J) Experimental results for completing the first level of the Super Mario Bros. video game in real time in response to a preprogrammed PG input (PS programmed to remain constant). Callouts include the controller activation state, the game state, and an image of the soft robotic hand using the controller corresponding to demonstrative time points; see also movie S6. Photo credit: Joshua D. Hubbard, Ruben Acevedo and Kristen M. Edwards, University of Maryland, College Park.
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