Sensitivity of the sensor is of great importance in practical applications of wearable electronics or smart robotics. In the present study, a capacitive sensor enhanced by a tilted micropillar array-structured dielectric layer is developed. Because the tilted micropillars undergo bending deformation rather than compression deformation, the distance between the electrodes is easier to change, even discarding the contribution of the air gap at the interface of the structured dielectric layer and the electrode, thus resulting in high pressure sensitivity (0.42 kPa–1) and very small detection limit (1 Pa). In addition, eliminating the presence of uncertain air gap, the dielectric layer is strongly bonded with the electrode, which makes the structure robust and endows the sensor with high stability and reliable capacitance response. These characteristics allow the device to remain in normal use without the need for repair or replacement despite mechanical damage. Moreover, the proposed sensor can be tailored to any size and shape, which is further demonstrated in wearable application. This work provides a new strategy for sensors that are required to be sensitive and reliable in actual applications.

Strain sensors combining high sensitivity with good transparency and flexibility would be of great usefulness in smart wearable/flexible electronics. However, the fabrication of such strain sensors is still challenging. In this study, new strain sensors with embedded multiwalled carbon nanotubes (MWCNTs) meshes in polydimethylsiloxane (PDMS) films were designed and tested. The strain sensors showed elevated optical transparency of up to 87% and high sensitivity with a gauge factor of 1140 at a small strain of 8.75%. The gauge factors of the sensors were also found relatively stable since they did not obviously change after 2000 stretching/releasing cycles. The sensors were tested to detect motion in the human body, such as wrist bending, eye blinking, mouth phonation, and pulse, and the results were shown to be satisfactory. Furthermore, the fabrication of the strain sensor consisting of mechanically blading MWCNTs aqueous dispersions into microtrenches of prestructured PDMS films was straightforward, was low cost, and resulted in high yield. All these features testify to the great potential of these sensors in future real applications.

Gecko-inspired dry adhesion has attracted much attention for many applications such as soft grippers and wall-climbing robots, which, however, demonstrate stable adhesion on flat surfaces and small adhesion on nonflat surfaces. In practice, geckos’ capability of walking upside down on both flat and nonflat surfaces comes from the combined action of adhesive structures for passive adhesion and toe muscles for stiffness modulation. Inspired by this behavior, this study proposes a hierarchal adhesive structure for high and switchable adhesion on nonflat surfaces. The three-layer adhesive consists of a mushroom-shaped structure top layer, stiffness modulation thermoplastic polyurethane (middle layer), and an electrothermal film (bottom layer) that mimics the epidermal adhesive structures, toe muscles, and electromyographic signals, respectively. Through the tunable structural stiffness controlled by adjusting the voltage, the adhesive force can be increased by 1 or 2 orders of magnitude compared to the conventional adhesive structures and further used for attachment and detachment functions. The gecko-inspired soft gripper is successfully tested as a pick-up and drop-down system for transporting a surface with different features, which has great application potential in industrial lines and daily life.

Bioinspired structural adhesives that are capable of bonding two objects together have recently found widespread applications in industrial fields, because of their promising reusability and environmental friendliness. However, such adhesives are usually monofunctional and cannot yield real‐time detection on the adhesion status, which is important for both biological systems (e.g., Gecko) and engineered mimics. This study reports a new hierarchical structure with the monolithic integration of adhesion and sensing functions, namely, contact‐sensible adhesive (CSA). The proposed CSA is composed of mushroom‐shaped microstructures on the top layer for providing strong adhesion, and a pillar array sandwiched by a pair of foil electrodes on the bottom layer as a compliant backing and a capacitive sensor. The CSA is not only sensitive to the external pressure, tension, and shear loads, but also shows enhanced adhesion on uneven surfaces, due to the high compliance of the hierarchical system. As a proof of concept, the as‐prepared CSA is applied as a contact interface in a gripper to complete the grasping task.

No abstract

The epidermal adhesive structure of many animals generates reliable adhesion on their engaged surfaces. However, current bio-inspired adhesion structures are difficult to function well in dry and underwater environments simultaneously. Interestingly, the male Dytiscus lapponicus attaches firmly to the rough shell of the female D. lapponicus in both dry and underwater conditions owing to the adhesive setae of its forelegs, and to the best of our knowledge, designing adhesive structures on multienvironments has never been reported. Here, a D. lapponicus-inspired adhesion structure (DIAS) is proposed and fabricated using double-exposure-fill molding technology accompanied with the material curing shrinkage, in which different structural features could be achieved by varying curing shrinkage ratios, elastic moduli, and back exposure time. The DIAS offered high, reversible, and repeatable strength in dry and underwater conditions with values of 205 and 133 kPa, respectively. By comparing the adhesion properties of different shapes via testing experiments and numerical analysis, a structural feature with an inclination of 15° was found to be optimal. Finally, the potential application of the DIAS in flexible electronic smart skin-attachable devices was demonstrated on a pig skin, paving the way for further bio-inspired adhesive designs for both dry and wet scenarios.

Inspired by the prominent adhesion ability of octopus suckers, many dry/wet adhesives with specific micro-structure have been fabricated for applications in smart robots, manipulators, and medical treatments. However, the reported octopus-inspired adhesive patches are either suction-assistant without tightsealing, or suction-sealed but inefficient under both dry/wet environments. Here, a microtemplated electrowetting method is developed for the fabrication of reversible dry/wet adhesive pads consisting of extruded microsuckers with suction-enhanced microdomes and sealing-ring tips. The mechanism toward the morphology regulation of microdomes illustrates the uneven electrohydrodynamic force on the liquid-air interface that changes the liquid meniscus and achieves the precise regulation of the microdomes curvature ratio (from 0.45 to 0.74). The tip spacing can be controlled (from 0 to 50 µm) by using different templates. Theoretical and experimental insights into the mechanism of the microdomes morphology and the tip spacing on adhesion are discussed. With optimized microdomes and maximized sealing-tips, this adhesive patch generates strong and repeatable adhesion on a silicon wafer in both air (≈ 86 kPa) and underwater (≈ 61 kPa) environments. Besides, considerable adhesion to the rough surfaces are also revealed. Its adhesion ability is demonstrated with stable transportation of various objects under air/underwater environments, providing a potential application in cross-media operation.

Bioinspired dry adhesives have an extraordinary impact in the field of robotic manipulation and locomotion. However, there is a considerable difference between artificial structures and biological ones regarding surface adaptability, especially for rough surfaces. This can be attributed to their distinct structural configuration and forming mechanism. Here, we propose a core–shell adhesive structure that is obtained through a growth strategy, i.e., an electrically responsive self-growing core–shell structure. This growth strategy results in a specific mushroom-shaped structure with a rigid core and a soft shell, which exhibits excellent adhesion on typical target surfaces with roughness ranging from the nanoscale to the microscale up to dozens of micrometers. The proposed adhesion strategy extends dry adhesives from smooth surfaces to rough ones, especially for rough surfaces with roughness up to dozens or hundreds of micrometers, opening an avenue for the development of dry adhesive-based devices and systems.