Cephalopod-inspired robot capable of cyclic jet propulsion through shape change

Multimodal Locomotion in a Soft Robot Through Hierarchical Actuation

Soft and continuum robots present the opportunity for extremely large ranges of motion, which can enable dexterous, adaptive, and multimodal locomotion behaviors. However, as the number of degrees of freedom (DOF) of a robot increases, the number of actuators should also increase to achieve the full actuation potential. This presents a dilemma in mobile soft robot design: physical space and power requirements restrict the number and type of actuators available and may ultimately limit the movement capabilities of soft robots with high-DOF appendages. Restrictions on actuation of continuum appendages ultimately may limit the various movement capabilities of soft robots. In this work, we demonstrate multimodal behaviors in an underwater robot called "Hexapus." A hierarchical actuation design for multiappendage soft robots is presented in which a single high-power motor actuates all appendages for locomotion, while smaller low-power motors augment the shape of each appendage. The flexible appendages are designed to be capable of hyperextension for thrust, and flexion for grasping with a peak pullout force of 32 N. For propulsion, we incorporate an elastic membrane connected across the base of each tentacle, which is stretched slowly by the high-power motor and released rapidly through a slip-gear mechanism. Through this actuation arrangement, Hexapus is capable of underwater locomotion with low cost of transport (COT = 1.44 at 16.5 mm/s) while swimming and a variety of multimodal locomotion behaviors, including swimming, turning, grasping, and crawling, which we demonstrate in experiment.

Optimal design and development of a fast steering robot inspired by scallops

The improvement of the steering performance of jet robots is challenging due to single inflexible jet aperture. Scallops provide a potential solution with hard shells and a double-hole jet propulsion, which are expected to achieve fast steering movement under water. Inspired by scallops, a bionic propulsion dynamic mesh is proposed in this article, and a three-dimensional computational model of scallops is established. We further calculated the scallop propulsion mechanism under the swing of shells with different shapes. The coupling of simultaneous swing of two shells and their coupling with velum are presented, revealing the unique movement mechanism of Bivalvia. Based on this, the advantages of the double-hole jet propulsion are applied to develop a scallop robot with excellent steering capabilities. Experiments are conducted to verify the steering performance of the scallop robot.

Recent Advances in Sensor-Actuator Hybrid Soft Systems: Core Advantages, Intelligent Applications, and Future Perspectives

The growing demand for soft intelligent systems, which have the potential to be used in a variety of fields such as wearable technology and human-robot interaction systems, has spurred the development of advanced soft transducers. Among soft systems, sensor-actuator hybrid systems are considered the most promising due to their effective and efficient performance, resulting from the synergistic and complementary interaction between their sensor and actuator components. Recent research on integrated sensor and actuator systems has resulted in a range of conceptual and practical soft systems. This review article provides a comprehensive analysis of recent advances in sensor and actuator integrated systems, which are grouped into three categories based on their primary functions: i) actuator-assisted sensors for intelligent detection, ii) sensor-assisted actuators for intelligent movement, and iii) sensor-actuator interactive devices for a hybrid of intelligent detection and movement. In addition, several bottlenecks in current studies are discussed, and prospective outlooks, including potential applications, are presented. This categorization and analysis will pave the way for the advancement and commercialization of sensor and actuator-integrated systems.

Locomotion performance of an axisymmetric 'flapping fin'

Inspired by the jet-propulsion mechanism of aquatic creatures such as sea salps, a novel locomotion system based on an axisymmetric body design is proposed. This system consists of an empty tube with two ends open. When the diameters of the front and back openings are changed periodically, the forward-backward symmetry is broken so that the system starts swimming. Viewed within a cross section, this system resembles a two-dimensional flapping fin with its leading edge located at the front opening and the trailing edge at the back opening. The feasibility of this system has been proven via numerical simulations using a fluid-structure interaction model based on the immersed-boundary framework. According to the results, at relatively low Reynolds number (O(102)), this simple locomotion method can easily achieve a mean swimming speed of 2 to 3 body lengths per deformation period. Further simulations illustrate the following characteristics: (1) within the chamber, the hydrodynamic interactions among different parts of the body leads to a performance-enhancing mechanism similar to the ground effect; (2) reducing the diameter of the body can strengthen this effect so that both the swimming speed and the energy efficiency are improved; (3) for better performance the amplitude of diameter oscillation at the trailing edge should be larger or at least equal to the one at the leading edge.

New Method for Rapid 3D Reconstruction of Semi-Transparent Underwater Animals and Structures

Morphological features are the primary identifying properties of most animals and key to many comparative physiological studies, yet current techniques for preservation and documentation of soft-bodied marine animals are limited in terms of quality and accessibility. Digital records can complement physical specimens, with a wide array of applications ranging from species description to kinematics modeling, but options are lacking for creating models of soft-bodied semi-transparent underwater animals. We developed a lab-based technique that can live-scan semi-transparent, submerged animals, and objects within seconds. To demonstrate the method, we generated full three-dimensional reconstructions (3DRs) of an object of known dimensions for verification, as well as two live marine animals-a siphonophore and an amphipod-allowing detailed measurements on each. Techniques like these pave the way for faster data capture, integrative and comparative quantitative approaches, and more accessible collections of fragile and rare biological samples.

A versatile jellyfish-like robotic platform for effective underwater propulsion and manipulation

Underwater devices are critical for environmental applications. However, existing prototypes typically use bulky, noisy actuators and limited configurations. Consequently, they struggle to ensure noise-free and gentle interactions with underwater species when realizing practical functions. Therefore, we developed a jellyfish-like robotic platform enabled by a synergy of electrohydraulic actuators and a hybrid structure of rigid and soft components. Our 16-cm-diameter noise-free prototype could control the fluid flow to propel while manipulating objects to be kept beneath its body without physical contact, thereby enabling safer interactions. Its against-gravity speed was up to 6.1 cm/s, substantially quicker than other examples in literature, while only requiring a low input power of around 100 mW. Moreover, using the platform, we demonstrated contact-based object manipulation, fluidic mixing, shape adaptation, steering, wireless swimming, and cooperation of two to three robots. This study introduces a versatile jellyfish-like robotic platform with a wide range of functions for diverse applications.

Wall effect on the start maneuver of a jet swimmer

Inspired by aquatic creatures such as squid, the novel propulsion method based on pulsed jetting is a promising way to achieve high speed and high maneuverability. To study the potential application of this locomotion method in confined space with complicated boundary conditions, it is critical to understand their dynamics in the vicinity of solid boundaries. In this study we numerically examine the start maneuver of an idealized jet swimmer near a wall. Our simulations illustrate three important mechanisms: (1) due to the blocking effect of the wall the pressure inside the body is affected so that the forward acceleration is increased during deflation and decreased during inflation; (2) the wall affects the internal flow so that the momentum flux at the nozzle and subsequently the thrust generation during the jetting phase are slightly increased; (3) the wall affects the wake so that the refilling phase is influenced, leading to a scenario in which part of the energy expended during jetting is recovered during refilling to increase forward acceleration and reduce power expenditure. In general, the second mechanism is weaker than the other two. The exact effects of these mechanisms depend on physical parameters such as the initial phase of the body deformation, the distance between the swimming body and the wall, and the Reynolds number.

Soft robotics towards sustainable development goals and climate actions

Soft robotics technology can aid in achieving United Nations’ Sustainable Development Goals (SDGs) and the Paris Climate Agreement through development of autonomous, environmentally responsible machines powered by renewable energy. By utilizing soft robotics, we can mitigate the detrimental effects of climate change on human society and the natural world through fostering adaptation, restoration, and remediation. Moreover, the implementation of soft robotics can lead to groundbreaking discoveries in material science, biology, control systems, energy efficiency, and sustainable manufacturing processes. However, to achieve these goals, we need further improvements in understanding biological principles at the basis of embodied and physical intelligence, environment-friendly materials, and energy-saving strategies to design and manufacture self-piloting and field-ready soft robots. This paper provides insights on how soft robotics can address the pressing issue of environmental sustainability. Sustainable manufacturing of soft robots at a large scale, exploring the potential of biodegradable and bioinspired materials, and integrating onboard renewable energy sources to promote autonomy and intelligence are some of the urgent challenges of this field that we discuss in this paper. Specifically, we will present field-ready soft robots that address targeted productive applications in urban farming, healthcare, land and ocean preservation, disaster remediation, and clean and affordable energy, thus supporting some of the SDGs. By embracing soft robotics as a solution, we can concretely support economic growth and sustainable industry, drive solutions for environment protection and clean energy, and improve overall health and well-being.

Fabrication, control, and modeling of robots inspired by flagella and cilia

Flagella and cilia are slender structures that serve important functionalities in the microscopic world through their locomotion induced by fluid and structure interaction. With recent developments in microscopy, fabrication, biology, and modeling capability, robots inspired by the locomotion of these organelles in low Reynolds number flow have been manufactured and tested on the micro-and macro-scale, ranging from medicalin vivomicrobots, microfluidics to macro prototypes. We present a collection of modeling theories, control principles, and fabrication methods for flagellated and ciliary robots.

Thrust and torque production of a squid-inspired swimmer with a bent nozzle for thrust vectoring

A three-dimensional pulsed-jet propulsion model consisting of a flexible body and a steerable bent nozzle in tethered mode is presented and studied numerically. By prescribing the body deformation and nozzle angle, we examine the flow evolution and propulsive/turning performance via thrust vectoring. Our results show that the vortex ring is no longer axis-symmetric when the jet is ejected at an angle with the incoming flow. A torque peak is observed during jetting, which is mainly sourced from the suction force (negative pressure) at the lower part of the internal nozzle surface when the flow is directed downward through an acute angle. After this crest, the torque is dominated by the positive pressure at the upper part of the internal nozzle surface, especially at a relatively low jet-based Reynolds number (O(10²)). The torque production increases with a larger nozzle bent angle as expected. Meanwhile, the thrust production remains almost unchanged, showing little trade-off between thrust and torque production which demonstrates the advantage of thrust vectoring via a bent nozzle. By decoupling the thrust at the internal and outer surfaces considering special characteristics of force generation by pulsed-jet propulsion, we find that variations in Reynolds number mostly affect the viscous friction at the outer surfaces. The influence of the maximum stroke ratio is also studied. Results show that both the time-averaged thrust and the torque decrease at a larger stroke ratio.

Physics and applications of squid-inspired jetting

In the aquatic world jet propulsion is a highly successful locomotion method utilized by a variety of species. Among them cephalopods such as squids excel in their ability for high-speed swimming. This mechanism inspires the development of underwater locomotion techniques which are particularly useful in soft-bodied robots. In this overview we summarize existing studies on this topic, ranging from investigations on the underlying physics to the creation of mechanical systems utilizing this locomotion mode. Research directions that worth future investigation are also discussed.

Near-Infrared Light-Driven Shape-Programmable Hydrogel Actuators Loaded with Metal-Organic Frameworks

Shape-programmable hydrogel-based soft actuators that can adaptively respond to external stimuli are of paramount significance for the development of bioinspired aquatic smart soft robots. Herein, we report the design and synthesis of near-infrared (NIR) light-driven hydrogel actuators through in situ photopolymerization of poly(N-isopropylacrylamide) (PNIPAM) hydrogels loaded with metal-organic frameworks (MOFs) onto the surface of the poly(dimethylsiloxane) (PDMS) thin film. The MOFs can not only function as an excellent photothermal nanotransducer but also accelerate the adsorption/desorption of water due to their porous nanostructure, which speeds up the response rate of the actuators. Shape-programmable hydrogel actuators are fabricated by tailoring the patterning of PDMS thin film, and thus different shape-morphing modes such as directional bending and chiral twisting are observed under the NIR light irradiations. As the proof-of-concept demonstrations, an artificial hand, biomimetic mimosa, and flower are conceptualized with light-driven MOF-containing hydrogel actuators. Interestingly, we are able to achieve an octopus-inspired light-driven soft swimmer upon cyclic NIR illumination due to the fast photoresponsiveness of as-prepared hydrogel actuators. This work can offer insights for fabricating programmable and reconfigurable smart aquatic soft actuators, thus shining a light into their potential applications in emerging fields including soft robots, biomedical devices, and beyond.

Free swimming of a squid-inspired axisymmetric system through jet propulsion

An axisymmetric fluid-structure interaction model based on the immersed-boundary approach is developed to study the self-propelled locomotion of a squid-inspired swimmer in relatively low Reynolds numbers (O(102)). Through cyclic deformation, the swimmer generates intermittent jet flow, which, together with the added-mass effect associated with the body deformation, provides thrust. Through a control volume analysis we are able to determine the jet-related thrust. By adding it to the added-mass-related thrust we separate the net thrust on the body from the drag effect due to forward motion, so that the propulsion efficiency in free swimming is found. This numerical algorithm and thrust-drag decomposition method are used to study the dynamics of the bio-inspired locomotion system in different conditions, whereby the performance is characterized by the aforementioned propulsion efficiency as well as the conventionally defined cost of transport.