Biomimetic Robot Research Articles

Design of asymmetric-adhesion lignin-reinforced hydrogels based on disulfide bond crosslinking for strain sensing application

Soft and elastic polymer hydrogel materials are booming in the fields of wearable biomimetic skin, sensors, robotics, and bioelectrodes. Currently, many researchers are exploring new chemistries for the preparation of hydrogels to improve their performance. In the present study, we design and develop a strategy to prepare lignin reinforced hydrogels based on disulfide bond crosslinking mechanisms, and resultant hydrogels exhibit excellent stretchability, with tensile strain of up to 1085.4%, and high adhesion (with the highest T-peel strength of up to 432.2 N/m to pigskin). The underlying mechanism is based on the disulfide bonds that act as crosslinkers in the as-prepared hydrogel, and they can be easily cleaved and re-formed under mild conditions. Thanks to the presence of lignin, the as-obtained hydrogels also have excellent UV shielding effect. When assembled into a strain sensor, they can output stable and sensitive sensing signals, with gauge factor (GF) of 2.72 (strain: 0–72.8%). Furthermore, a simple and effective strategy to construct asymmetric adhesive hydrogels was adopted, which is based on directional soaking of the top portion of the hydrogel in a high-concentrated calcium chloride solution. The asymmetric hydrogel strain sensor transmits accurate and stable signals without the interference of various contaminants.

Self-Sensing Actuators Based on a Stiffness Variable Reversible Shape Memory Polymer Enabled by a Phase Change Material.

Soft actuators with integrated mechanical and actuation properties and self-sensing ability are still a challenge. Herein, a stiffness variable polyolefin elastomer (POE) with a reversible shape memory effect is prepared by introducing a typical phase change material, i.e., paraffin wax (PW). It is found that the variable stiffness of POE induced by PW can balance the reversible strain and load-bearing capability of actuators. Especially, carbon nanotubes (CNTs) are concentrated in a thin surface layer by spraying and hot pressing in the soft state of POE/PW blends, providing signal transductions for the strain and temperature perception for actuators. Taking advantage of tunable reversible deformation and mechanical transformation of the POE/PW actuator, different biomimetic robotics, including grippers with high load-bearing capability (weight-lifting ratio > 146), walking robots that can sense angles of joints, and high-temperature warning robots are demonstrated. A scheme combining the variable stiffness and electrical properties provides a versatile strategy to integrate actuation performance and self-sensing ability, inspiring the development of multifunctional composite designs for soft robotics.

A comprehensive review on fish-inspired robots

Recently, the increasing interest in underwater exploration motivates the development of aquatic unmanned vehicles. To execute hazardous tasks in an unknown or even hostile environment, researchers have directed on developing biomimetic robots inspired by the extraordinary maneuverability, cruising speed, and propulsion efficiency of fish. Nevertheless, the performance of current prototypes still has gaps compared with that of real fishes. In this review, recent approaches in structure designs, actuators, and sensors are presented. In addition, the theoretical methods for modeling the robotic fishes are consolidated, and the control strategies are offered. Finally, the current challenges are summarized, and possible future directions are deeply discussed. It is expected that the emergence of new engineering and biological technologies will enhance the field of robotic fish for further advancement.

Editorial: Focus on research from China in Bioinspiration & Biomimetics

This special issue "Focus on research from China in Bioinspiration & Biomimetics" aims to show the recent research progress from several representative labs from China. This issue contains 12 papers divided into three sub-fields: biomimetic terrestrial robots, biomimetic aerial robotics, and biomimetic underwater robotics. This editorial paper aims to provide a brief introduction to these papers.

A Brief Overview of Bioinspired Robust Hydrogel Based Shape Morphing Functional Structure for Biomedical Soft Robotics

Biomimetic and soft robotics research has been inspired by many biological organisms focusing on soft structural composites reinforced by stiff constituents. In the case of synthetic soft structural materials, hydrogels are very similar to the biological soft tissues/organs, owing to their “wet and soft” properties, their elastic performance, biodegradability, and biocompatibility. However, the current scope of hydrogel applications is usually hampered by their feeble mechanical properties. Although significant progress has been made in developing intense, challenging, and stretchable hydrogels, it is still challenging to realize the optimal magnitude of physical and mechanical properties altogether in synthetic hydrogels. This review briefly focuses on the hydrogel fibrous shape-morphing composite structure and its functionalities. The nature-inspired, fiber-reinforced soft hydrogel shape-morphing functional composite structure delivers them a cartilage-like anisotropic behavior. They could have broad potential applications in various areas, including tissue engineering, soft robotics, stretchable and bio-integrated electronics, microfluidics, and biomedical devices.

Research Progress of Bionic Water Strider Robot

Background: The bionic water strider robot can achieve sliding, jumping, and other movements on the water surface, having advantages of small size, light weight, flexible movements, and other characteristics. It can detect the quality of water, investigate and search the water surface, and perform some other operations. It has a very broad range of applications and development prospects. Therefore, the trend of biomimetic water strider robots is attracting more and more attention. Objective: This study aimed to review the bionic water strider robot and introduce its classification, characteristics, and development. Methods: This paper reviews various productions and patents related to the bionic water strider robot from 2003 to the present. The sources of the papers include CNKI, Wanfang, Patent publication announcement in China, Web of Science, IEEE, Elsevier, Springer-Verlag, Espacenet, and FPO IP Research & Communities. To obtain the results, an endnote was used for documentation, and citeSapce was used for visual analysis. Results: The mechanical structure of existing bionic water strider robots has been analyzed and compared. Furthermore, the typical characteristics are concluded. The main problems in its development are analyzed, and the development trend is foreseen. Furthermore, the current and future research prospects of the productions and patents on the bionic water strider robot are discussed. Conclusion: The optimization and development of the structure of the bionic water strider robot and the development of associated components help to improve the simulation of the water strider's motion and perform a better task in a complex water surface environment. In the future, with the improvement in the research, the bionic water strider robot will develop into miniaturization, intelligence, and integration.

Biomimetic omnidirectional multi-tail underwater robot

Biomimetics adopted as a basis for underwater robotic design to enhance locomotion efficiency, maneuverability, and adaptability has shown an extraordinary vitality and enormous growth potential in the field of underwater robotics. However, most designs are focused on mimicry of a specific aquatic organism or its specific function. Biomimetic approaches to underwater robot design that incorporate combination and coordination of multiple individuals could provide a powerful vehicle to build robotic systems that could go far beyond simply mimicking a specific aquatic organism, which remains largely unexplored. With an increasing requirement of underwater robots in context of professional explorations, measurements, and inspections, the demand for underwater robots with high stability and maneuverability has become more urgent. To this end, this study aims at presenting a novel biomimetic design of an omnidirectional underwater robot with multiple tails. This designed underwater robot with multiple tails is capable of combining different advantageous locomotion modes from fish, frog, octopus, fish swarm, and dolphin formation. Swimming locomotion modes including forward motion, steering, sinking, rising and their combinations can be realized flexibly. The robot can easily switch between arbitrary locomotion modes to achieve fast changes of swimming directions in 3D space. Full demonstrations of swimming locomotion modes and their flexible switch are presented to show the robot’s excellent performance on stability, mobility, and maneuverability. The maximum forward velocity and steering angular velocity of the designed robot in this study can correspondingly reach 1.160 m/s (1.93BL) and 115.7 ∘/s. The resulting prototype is experimentally verified in a laboratory water tank with waves. The robot could be the first of its kind achieving higher stability, mobility, and maneuverability of great potential in working in complex dynamic water environments, and thus would present an alternative and new insight into underwater robotic design and control, focusing on complex water environments.

Learning for Attitude Holding of a Robotic Fish: An End-to-End Approach With Sim-to-Real Transfer

Controlling biomimetic underwater robots in unknown flow fields remains a challenge due to the strong nonlinearity of the fluid. This article investigates the attitude holding task of a robotic fish swimming in reality. Such a typical sensing-based control task requires the fish to keep a desired angle of attack in an unknown and even varied incoming flow. To this end, we propose a learning-based approach by using a deep neural network directly maps the raw data of sensors equipped on the robot to the continuous control signals in an end-to-end manner. First, based on experimental data of the physical robot, we construct a data-driven simulation environment including three modules of dynamic, sensor, and control. The dynamic and sensor modules are established to model the dynamics of the fish and to generate its sensors’ data, based on which a deep reinforcement learning (DRL) algorithm in the control module is trained to get a control policy. Then, we directly deploy the trained policy to a physical robotic fish for attitude holding task. Experimental results demonstrate the robustness and effectiveness of the DRL policy and, thus, verify the success of our approach to achieving sim-to-real transfer.

Ultrasensitive Pressure Sensor Sponge Using Liquid Metal Modulated Nitrogen-Doped Graphene Nanosheets.

Wearable pressure sensors are crucial for real-time monitoring of human activities and biomimetic robot status. Here, the ultrasensitive pressure sensor sponge is prepared by a facile method, realizing ultrasensitive pressure sensing for wearable health monitoring. Since the liquid metal in the sponge-skeleton structure under pressure is conducive to adjust the contact area with nitrogen-doped graphene nanosheets and thus facilitates the charge transfer at the interface, such sensors exhibit a fast response and recovery speed with the response/recovery time 0.41/0.12 s and a comprehensive response range with a sensitivity of up to 476 KPa-1. Notably, the liquid metal-based spongy pressure sensor can accurately monitor the human body's pulse, the pressure on the skin, throat swallowing, and other activities in real time, demonstrating a broad application prospect. Those results provide a convenient and low-cost way to fabricate easily perceptible pressure sensors, expanded the application potential of liquid metal-based composites for future electronic skin development.

High Energy and Power Density Peptidoglycan Muscles through Super-Viscous Nanoconfined Water.

Water‐responsive (WR) materials that reversibly deform in response to humidity changes show great potential for developing muscle‐like actuators for miniature and biomimetic robotics. Here, it is presented that Bacillus (B.) subtilis’ peptidoglycan (PG) exhibits WR actuation energy and power densities reaching 72.6 MJ m−3 and 9.1 MW m−3, respectively, orders of magnitude higher than those of frequently used actuators, such as piezoelectric actuators and dielectric elastomers. PG can deform as much as 27.2% within 110 ms, and its actuation pressure reaches ≈354.6 MPa. Surprisingly, PG exhibits an energy conversion efficiency of ≈66.8%, which can be attributed to its super‐viscous nanoconfined water that efficiently translates the movement of water molecules to PG's mechanical deformation. Using PG, WR composites that can be integrated into a range of engineering structures are developed, including a robotic gripper and linear actuators, which illustrate the possibilities of using PG as building blocks for high‐efficiency WR actuators.

3D-printable colloidal photonic crystals

The architecture of the colloidal photonic crystals (CPCs) is of paramount importance to their functionality and applications. Nevertheless, the realization of CPCs with arbitrarily designed, volumetrically sophisticated structures at the macroscale remains challenging. In this work, a printable CPC ink was developed. By combining this ink with a digital light processing (DLP)-based three-dimensional (3D) printing system, we were able to fabricate the CPC superstructures featuring both digitally defined macroscale geometries and structural colors originating from the ordered structures at the sub-micron scale. Moreover, besides the arbitrarily adjustable and precisely designable architectures, the optical properties, mechanical performances, and stimuli-responsiveness of the printed objects could also be facilely tuned by the composition of the ink or the printing parameters of the DLP system. This technology endows us the ability to fabricate CPCs with a multitude of desirable functions as well as mimic the hierarchical structures and color-manipulation strategies of some creatures in nature, which paves the way for potentially broad applications in intelligent color displays, 3D integrated sensors, biomimetic color-morphing soft robots, and smart anti-counterfeiting labels, among others.

Ultra-Stretchable and Fast Self-Healing Ionic Hydrogel in Cryogenic Environments for Artificial Nerve Fiber.

Self-healing materials behave with irreplaceable advantages in biomimetic intelligent robots (BIR) for avoiding or reducing safety hazards and economic losses from accidental damage during service. However, the self-healing ability is unreservedly lost and even becomes rigid and fragile in the cryogenic environment where BIR are precisely needed. Here, the authors report a versatile ionic hydrogel with fast self-healing ability, ultra-stretchability, and stable conductivity, even at -80°C. The hydrogel is systematically optimized to improve a hydrogen-bonded network nanostructure, coordinated achieving a quick self-healing ability within 10min, large deformation tolerance of over 7000%, superior conductivity of 11.76 S cm-1 and anti-freezing ability, which is difficult to obtain simultaneously. Such a hydrogel provides new opportunities for artificial electronic devices in harsh environments. As a prospective application, they fabricate an artificial nerve fiber by mimicking the structure and functions of the myelinated axon, exhibiting the property of fast and potential-gated signal transmission. This artificial nerve fiber is integrated into a robot for demonstrating a real-time high fidelity and high throughput information interaction under big deformation and cryogenic temperature. The hydrogel and bionic device will bring pioneering functions for robots and open a broad application scenario in extreme conditions.

PEDOT:PSS/Bacterial Cellulose-based soft actuator under triangle and square wave: Deflection, response and fidelity

Poly(3,4-ethylene dioxythiophene) polystyrene sulfonate (PEDOT:PSS) is a preferred conducting polymer owing to its high conductivity and processability. PEDOT: PSS on the application of a potential bias can transact ions with surrounding electrolyte causing a volume change. This reversible volume change is exploited to prepare a bilayer actuator with bacterial cellulose as the substrate. The actuation response is compared for two waveforms – square wave and triangular wave. A large deflection of 5.2 mm per voltage applied was observed for the square wave with a maximum voltage of 1.5 V and a dwell time of 20 s. An in-house developed method based on a smartphone camera was used to track and measure the deflection. Effect of voltage and frequency are also reported to get insights into the mechanism of actuation. This electro-chemo-mechanical soft actuator can have potential applications in biomimetic soft robotics.

A Novel Modular Biomimetic Live Working Robot for Power Distribution Line

Live working on power distribution lines is an effective way to improve the reliability of power supply. The aerial lift device with an insulated boom is often used as a platform to carry out live working, which is difficult to carry out in mountainous areas, paddy fields, and other complex environments. At the same time, power distribution live working requires highly skilled operators, and a lot of personal security measures, which is not conducive to the application in some developing countries. We imagine that the solution of the above problem is to use a robot to climb up the pole and complete the live working instead of the operator. In this article we report a low-cost modular biomimetic robot. The structure of the robot is designed to meet the requirements of live working, and the motion mechanism of the robot climbing poles and performing live work is analyzed. The feasibility of the technology is verified through simulation, experiments, and tests.

Real-time parametric estimation of periodic wake-foil interactions using bioinspired pressure sensing and machine learning

Periodic wake-foil interactions occur in the collective swimming of bio-inspired robots. Wake interaction pattern estimation (and control) is crucial to thrust enhancement and propulsive efficiency optimization. In this paper, we study the wake interaction pattern estimation of two flapping foils in tandem configurations. The experiments are conducted at a Reynolds number of 1.41 × 104 in a water channel. A modified wake-foil phase parameter Φ, which unifies the influences of inter-foil distance L x , motion phase difference Δφ and wake convection velocity U v , is introduced to describe the wake interaction patterns parametrically. We use a differential pressure sensor on the downstream foil to capture wake interaction characteristics. Data sets at different tandem configurations are collected. The wake-foil phase Φ is used to label the pressure signals. A one-dimensional convolutional neural networks (1D-CNN) model is used to learn an end-to-end mapping between the raw pressure measurements and the wake-foil phase Φ. The trained 1D-CNN model shows accurate estimations (average error 3.5%) on random wake interaction patterns and is fast enough (within 40 ms). Then the trained 1D-CNN model is applied to online thrust enhancement control of a downstream foil swimming in a periodic wake. Synchronous force monitoring and flow visualization demonstrate the effectiveness of the 1D-CNN model. The limitations of the model are discussed. The proposed approach can be applied to the online estimation and control of wake interactions in the collective swimming and flying of biomimetic robots.

Development of amphibious biomimetic robots

Development of amphibious biomimetic robots

Tentacled snakes-inspired flexible pressure sensor for pain sensation monitoring

Exploration of flexible tactile sensors with high sensitivity that can imitate the perception functions (tactile sensing and pain sensing) of human skin is the main force in the realization of electronic skin. The research of electronic skin with the function of pain perception is of great significance in the field of biomimetic robot and treatment of patients losing the pain sensation ability of their skin. Herein, to broaden the application field of traditional electronic skin, we demonstrate a biomimetic and highly sensitive tactile sensor for realization of sensory functionalities of human skin. The structure of our sensor mimics the surface of the tentacles of tentacled snakes, which are strikingly sensitive mechanoreceptors. We design a tentacle-inspired flexible sensor by sandwiching the convex dielectric layer of PDMS/MXene microarrays between two flexible electrodes. It is found that the bioinspired sensor exhibits a high sensitivity of 3.61 kPa−1, a fast response time of 29 ms and a satisfactory stability, ensuring the ability in monitoring physiological signals. Finally, we present the application of the sensor for finger bending, international Morse code detection, and artery pulse detection. By presetting the pain thresholds of different areas of skin in a program, the sensor can identify and distinguish pressure data that exceed the pain threshold, realizing the detection of pain. In addition, it can be further applied on robot skins to assess the risk level of the working environment by monitoring its pressure data.

Recent advances in materials and applications for bioelectronic and biorobotic systems

AbstractThe ultimate goal of the advancements in bioelectronics and robotics is the creation of seamless interfaces between artificial devices and biological structures. Current efforts in this area have been focused on designing biocompatible, mechanically compliant, and minimally invasive electronic and robotic systems for a range of applications, such as motor control and sweat sensing. The purposeful design of bioelectronic and robotic systems using the principles of biomimicry enables the creation of biocompatible and life‐like machines and electronics. The success of such approaches relies on the new development and applications of soft materials, as well as methods of actuation and sensing that are inspired, either by composition, function, or properties, of the naturally occurring organisms. A combination of rigid structural components, soft actuators, and flexible sensors can enable the integration of such devices with biological organisms and eventually human users. In this review, we highlight the recent advances in biomimetic soft robotics and bioelectronics. We describe the soft robotic fabrication toolbox and modern solution in bioelectronics that, in our opinion, will enable the fusion of these fields by creating robotic bioelectronic systems. Future development in this area will require substantial integration of adaptable and responsive components at the biointerfaces.

Tentacled snakes-inspired flexible pressure sensor for pain sensation monitoring

Abstract Exploration of flexible tactile sensors with high sensitivity that can imitate the perception functions (tactile sensing and pain sensing) of human skin is the main force in the realization of electronic skin. The research of electronic skin with the function of pain perception is of great significance in the field of biomimetic robot and treatment of patients losing the pain sensation ability of their skin. Herein, to broaden the application field of traditional electronic skin, we demonstrate a biomimetic and highly sensitive tactile sensor for realization of sensory functionalities of human skin. The structure of our sensor mimics the surface of the tentacles of tentacled snakes, which are strikingly sensitive mechanoreceptors. We design a tentacle-inspired flexible sensor by sandwiching the convex dielectric layer of PDMS/MXene microarrays between two flexible electrodes. It is found that the bioinspired sensor exhibits a high sensitivity of 3.61 kPa-1, a fast response time of 29 ms and a satisfactory stability, ensuring the ability in monitoring physiological signals. Finally, we present the application of the sensor for finger bending, international Morse code detection, and artery pulse detection. By presetting the pain thresholds of different areas of skin in a program, the sensor can identify and distinguish pressure data that exceed the pain threshold, realizing the detection of pain. In addition, it can be further applied on robot skins to assess the risk level of the working environment by monitoring its pressure data.

High-Precision Displacement and Force Hybrid Modeling of Pneumatic Artificial Muscle Using 3D PI-NARMAX Model

Pneumatic artificial muscle (PAM) is attractive in rehabilitation and biomimetic robots due to its flexibility. However, there exists a strong hysteretic nonlinearity in PAMs and strong coupling between the output displacement and the output force. At present, most commonly used hysteresis models can be treated as two-dimensional models, which only consider the nonlinearity between the input and the output displacement of the PAM without considering the coupling of the output force. As a result, high-precision modeling and estimation of the PAM’s behavior is difficult, especially when the external load of the system varies significantly. In this paper, the influence of the output force on the displacement is experimentally investigated. A three-dimensional model based on the modified Prandtl–Ishlinskii (MPI) model and the Nonlinear AutoRegressive Moving Average with eXogenous inputs (NARMAX) model is proposed to describe the relationship and couplings among the input, the output displacement, and the output force of the PAM. Experiments are conducted to verify the modeling accuracy of the proposed model when the external load of the PAM varies across a wide range. The experimental results show that the proposed model captures well the hysteresis and couplings of the PAM and can precisely predict the PAM’s behavior.