Xinping Zhou

The attraction or repulsion force between two solid objects at a liquid-gas interface (i.e. the lateral capillary interaction force) is generally considered to be highly dependent on both the shapes of the solid surfaces and the relative positions. To challenge this, we propose an exotic capillary system in which the stationary exotic plate piercing the interface can produce a constant capillary interaction force on a partly immersed cylinder at different horizontal positions. This constancy is owing to the counterbalancing of variations in the horizontal components of the surface tension force and the hydrostatic pressure force on the cylinder. Through analysing the meniscus profiles and the capillary interaction force in the proposed exotic capillary system, five types of exotic plate shapes are identified. More importantly, a further analysis indicates that the lateral capillary interaction force in the proposed exotic capillary system remains constant even for different vertical positions of the cylinder. To verify the practicality of our theory, a three-dimensional numerical investigation is conducted, and the results show that the lateral capillary interaction force can remain nearly constant as expected. The proposed capillary system provides new insight into controlling the capillary interaction force. The constant-force regimes suggest passive routes for interfacial transport and micromanipulation, force regulation and suppression of undesired capillary aggregation.

The biomimetic water strider robot is inspired by the biological water strider and is expected to be applied in fields such as environmental monitoring and reconnaissance. However, currently biomimetic water strider robots are mainly dominated by water pressure. This often leads to severe surface interference, high power consumption, and delayed response. Here, we introduce a lightweight (1.37 g) water surface skating biomimetic water strider robot driven by an electro‐ribbon actuator, which uses surface tension as the dominant force. This robot eliminates the need for a transmission system and achieves direct leg drive, minimizing energy loss and additional mass. Compared with other robots of the same type, this robot exhibits excellent performance, including fast response (millisecond level), minimal disturbance to the water surface (the pitch and swing angles are both below 0.2°), and lower cost of transportation (1.17 J kg ⁻¹ m ⁻¹ ). We further evaluated the motion stability of the robot. This work provides a foundation for the research of surface tension dominated biomimetic water strider robots and expands the application range of electro‐ribbon actuators.

Fluid–structure interaction (FSI) of the piston/cylinder interface critically affects the lubrication performance of axial piston pumps, yet its role under deep-sea conditions remains insufficiently understood. This study proposes an elastohydrodynamic (EHD) lubrication model for the piston/cylinder interface under deep-sea conditions, in which two-way FSI is realized through dynamic nodal data exchange. The proposed model integrates finite volume discretization of the Reynolds equation with finite element analysis of bushing deformation, and resolves the interdependence among film geometry, pressure distribution, and structural deformation by coupling piston dynamics with oil film lubrication equations within an iterative framework. The evolution of interfacial lubrication fields is characterized, and the effects of structural and operating parameters on energy consumption are quantified by comparing the EHD and hydrodynamic (HD) lubrication models. The results show that elastic deformation of the bushing under deep-sea conditions increases the leakage flow rate while reducing the viscous friction power loss. More importantly, although the leakage flow rate increases substantially with clearance, the EHD model reveals a non-monotonic dependence of viscous friction power loss on clearance, in contrast to the monotonic trend observed in the HD model. These findings provide useful guidance for the design and optimization of deep-sea axial piston pumps.

Flexible substrates are effective in suppressing splashing, but they simultaneously lead to inhibition of spreading (Howland et al. 2016 Phys. Rev. Lett. vol. 117 , 184502; Vasileiou et al. 2016 Proc. Natl Acad. Sci. USA vol. 113 , pp. 13307−13312). In addition, there has been limited investigation and no established scaling law for the splashing threshold in the case of flexible substrates. To address these points, this paper proposes a lotus-leaf-like disk that can effectively suppress droplet splashing without inhibiting the maximum spreading of droplets. This situation is numerically studied in this paper. Five dynamic modes of the impacting droplet are identified with various Weber numbers (defined as the inertia force relative to the surface tension force) and different disk’s stiffnesses. The threshold Weber number of splashing is developed by considering the flexibility of substrates. Finally, the results demonstrate that the proposed method not only suppresses the splashing but also maintains the maximum spreading.

Soft robotic joints demonstrate significant potential for enhancing robotic performance in complex environments through safe and powerful actuation. However, simultaneously achieving high torque, rapid response, angular displacement range, and long-term reliability in a single soft actuator remains a significant challenge. To address these challenges, we present an origami-inspired electrohydraulic soft (OES) joint that utilizes electrostatic actuation to control dielectric fluid displacement, enabling full deployment of the folded structure for precise bending motions. The OES joints demonstrate a blocking torque of 48.7 mN m and a specific torque of 19.44 N m/kg. The joints can be parametrically designed to achieve specific maximum bending angles within a wide range (0°–163°), a feature not demonstrated by other flexible joints in the literature. These advancements facilitate diverse robotic applications: (i) a jumping mechanism attaining 13.9 body-height leaps with 0.17 body lengths per second forward velocity, (ii) a crawling robot achieving 1.23 body lengths per second locomotion, (iii) a bidirectional actuator with programmable angular output, and (iv) a compliant gripper combining operational safety with high-force grasping capabilities.

Biomimetic robots, which abandon the rigid metal skeletons and joints of traditional industrial robots, offer superior environmental adaptability and movement flexibility. However, the actuators of bionic robots currently have limitations such as slow response, high power consumption, and complex structures. Here, we introduce a lightweight electro-ribbon actuator, which significantly improves performance through the addition of high dielectric constant silicone oil, and the actuation voltage has been reduced by 72% (to 2.76 kV). This direct-drive actuator eliminates the need for a transmission mechanism and has fast response and low power consumption characteristics. By utilizing these characteristics, we demonstrate a horizontal jumping robot (mass: 0.35 g) propelled 122 mm horizontally and 105 mm vertically under 12 kV actuation, with low cost of transport. Furthermore, a horizontal moving robot achieves voltage- and frequency-controlled motion via a spring-loaded return mechanism and intermittent electrostatic actuation. We also present a vertical jumping robot reaching 103 mm height within 0.167 s and a voltage-adjustable gripper. This study validates the electro-ribbon actuator as a promising solution for lightweight, fast-responding, and low-power biomimetic actuation, providing new ideas for biomimetic robot design.

The water striders demonstrate exceptional agility in dynamic water‐surface locomotion, enabling them to effectively avoid obstacles and evade predators. While current bioinspired jumping water strider robots predominantly rely on water pressure, which stores mechanical energy through elastic components to achieve transient high‐power output, these robots exhibit delayed actuation responses (>500 ms) and substantial hydrodynamic disturbances during actuation. Here, a centimeter‐scale jumping biomimetic water strider robot (mass: 0.21 g) that uses surface tension to jump on the water surface is presented. The robot employs an electro‐ribbon actuator, enabling sub‐second kinetics response, achieving vertical leaps of 128 mm with minimal surface perturbation. The gravitational potential energy of the robot at peak jumping height exceeds several orders of magnitude compared to the existing surface tension‐dominated jumping robot. Additionally, the study also systematically studies the interaction mechanism of dynamic contact between the robot's driving legs and the liquid‐air interface. This work provides new design principles for developing high‐performance biomimetic systems capable of dynamic fluid surface interactions.

The diversity of insect movements constitutes a key survival mechanism for obstacle avoidance and predatory escape behavior. As a representative aquatic insect, the water strider can skate quickly and freely on the water surface while ensuring its integrity. Utilizing this phenomenon, we propose a surface tension-dominated biomimetic water strider robot that can perform motion (linear skating and turning motion) on the gas–liquid interface. The robot has a maximum linear velocity of 14.2 cm/s and a maximum turning speed of 13.5 °/s. Compared to water pressure-dominated surface skating robots, this robot has the advantage of minimal surface disturbance. At the same time, the robot utilizes a combination of incomplete gear and face gear mechanical structures to achieve composite motion of the driving leg in both vertical and horizontal directions, restoring the spatial elliptical travel trajectory of the biological water strider driving leg end. In addition, this study also analyzed the fluid dynamics mechanism between the robot's driving legs and the water surface, as well as the stability of the water surface motion. This study provides new design criteria for the development of biomimetic water strider robots.