Bioinspired Microsphere-Embedded Adhesive Architectures for an Electrothermally Actuating Transport Device of Dry/Wet Pliable Surfaces

Bionic Design and Adsorption Performance Analysis of Vacuum Suckers

This study addresses the problem that the traditional method is not effective in improving the adsorption performance of vacuum suckers. From the perspective of bionics, the adsorption performance of bionic suckers based on the excellent adsorption of the abalone abdominal foot was studied. A bionic sucker was designed by extracting the sealing ring structure of the abdominal foot tentacle. The bionic sucker was subjected to tensile experiments using an orthogonal experimental design, and the adsorption of the bionic sucker was simulated and analyzed to explore its adsorption mechanism. The results show that the primary and secondary factors affecting the adsorption of the sucker are the number of sealing rings, the width of sealing rings and the spacing of sealing rings. At 60% vacuum, the bionic sucker with two sealing rings, a 1.5 mm sealing ring width and 3 mm sealing ring spacing has the largest adsorption force, and its maximum adsorption force is 15.8% higher than that of the standard sucker. This study shows that the bionic sucker design can effectively improve the adsorption performance of the sucker. The bionic sucker had a different stress distribution on the sucker bottom, which resulted in greater Mises stress in the sealing ring and the surrounding area, while the Mises stress in the central area of the sucker was smaller.

Adhesion Evolution: Designing Smart Polymeric Adhesive Systems with On-Demand Reversible Switchability

Smart polymeric switchable adhesives represent a rapidly emerging class of advanced materials, exhibiting the ability to undergo on-demand transitioning between "On" and "Off" adhesion states. By selectively tuning external stimuli triggers (including temperature, light, electricity, magnetism, and chemical agents), we can engineer these materials to undergo reversible changes in their bonding capabilities. The strategic design selection of stimuli is a pivotal factor in the design of switchable adhesive systems. This review outlines recent advancements in the field of smart switchable polymeric adhesives over the past decade with a focus on the selection of stimulus triggers. These systems are further categorized into one of four adhesion switching mechanisms upon initiation by a specific stimuli-trigger: (i) interfacial adhesion, (ii) stiffness, (iii) contact area, or (iv) suction-based switching. Evaluation of adhesion switching performance across systems is primarily made based on three key metrics: (i) maximum adhesion strength, (ii) switch ratio, and (iii) switch time. Different stimuli and mechanisms offer distinct advantages and limitations, influencing the performance characteristics and applicability of these materials across domains such as detachable biomedical devices, robotic grippers, and climbing robots. This review thus offers a perspective on the present advancements and challenges in this emerging field, along with insights into future directions.

Experimental Study on the Adhesion of Abalone to Surfaces with Different Morphologies

To date, research on abalone adhesion has primarily analyzed the organism's adhesion to smooth surfaces, with few studies on adhesion to non-smooth surfaces. The present study examined the surface morphology of the abalone's abdominal foot, followed by measuring the adhesive force of the abalone on a smooth force measuring plate and five force measuring plates with different surface morphologies. Next, the adhesion mechanism of the abdominal foot was analyzed. The findings indicated that the abdominal foot of the abalone features numerous stripe-shaped folds on its surface. The adhesion of the abalone to a fine frosted glass plate, a coarse frosted glass plate, and a quadrangular conical glass plate was not significantly different from that on a smooth glass plate. However, the organism's adhesion to a small lattice pit glass plate and block pattern glass plate was significantly different. The abalone could effectively adhere to the surface of the block pattern glass plate using the elasticity of its abdominal foot during adhesion but experienced difficulty in completely adhering to the surface of the quadrangular conical glass plate. The abdominal foot used its elasticity to form an independent sucker system with each small lattice pit, significantly improving adhesion to the small lattice pit glass plate. The elasticity of the abalone's abdominal foot created difficulty in handling slight morphological size changes in roughness, resulting in no significant differences in its adhesion to the smooth glass plate.

Abalone adhesion: The role of various adhesion forces and their proportion to total adhesion force

Adhesion is the basic ability of many kinds of animals in nature, which ensures the survival and reproduction of animal populations. The aquatic abalone has a strong adhesion capacity. In this study, we observed the microscopic morphology of abalone abdominal foot surface, and found that the surface was covered with a large number of fibers. Then five types of force measuring plates were designed and processed for the adhesion test of abalone abdominal foot. According to the test results, the composition of abalone abdominal foot adhesion force was analyzed and the proportion of various adhesion force to the total adhesion force of abalone abdominal foot was calculated. Among them, the vacuum adhesion force accounts for more than half of the total adhesion force of abalone abdominal foot, and its proportion is more than 60%. Van der Waals force also plays an important role, and its proportion is more than 20%. The proportion of capillary force is very small, which is only about 1%. Its main role is to form a liquid film to prevent the gas from flowing into the sucker. The vacuum adhesion of abalone abdominal foot can be further divided into the whole adhesion of abdominal foot, the local adhesion of abdominal foot and the frictional equivalent vacuum adhesion. And the whole adhesion of abdominal foot is basically equivalent to the local adhesion of abdominal foot. This study quantifies the proportion of various adhesion forces to the total adhesion force of the abdominal foot, which provides a reference for the further study of other adhesive creatures and the design of bionic underwater adhesion devices.

Advanced Bionic Attachment Equipment Inspired by the Attachment Performance of Aquatic Organisms: A Review

In nature, aquatic organisms have evolved various attachment systems, and their attachment ability has become a specific and mysterious survival skill for them. Therefore, it is significant to study and use their unique attachment surfaces and outstanding attachment characteristics for reference and develop new attachment equipment with excellent performance. Based on this, in this review, the unique non-smooth surface morphologies of their suction cups are classified and the key roles of these special surface morphologies in the attachment process are introduced in detail. The recent research on the attachment capacity of aquatic suction cups and other related attachment studies are described. Emphatically, the research progress of advanced bionic attachment equipment and technology in recent years, including attachment robots, flexible grasping manipulators, suction cup accessories, micro-suction cup patches, etc., is summarized. Finally, the existing problems and challenges in the field of biomimetic attachment are analyzed, and the focus and direction of biomimetic attachment research in the future are pointed out.

Soft Microdenticles on Artificial Octopus Sucker Enable Extraordinary Adaptability and Wet Adhesion on Diverse Nonflat Surfaces

Bioinspired soft devices, which possess high adaptability to targeted objects, provide promising solutions for a variety of industrial and medical applications. However, achieving stable and switchable attachment to objects with curved, rough, and irregular surfaces remains difficult, particularly in dry and underwater environments. Here, a highly adaptive soft microstructured switchable adhesion device is presented, which is inspired by the geometric and material characteristics of the tiny denticles on the surface of an octopus sucker. The contact interface of the artificial octopus sucker (AOS) is imprinted with soft, microscale denticles that interact adaptably with highly rough or curved surfaces. Robust and controllable attachment of the AOS with soft microdenticles (AOS-sm) to dry and wet surfaces with diverse morphologies is achieved, allowing conformal attachment on curved and soft objects with high roughness. In addition, AOS-sms assembled with an octopus-arm-inspired soft actuator demonstrate reliable grasping and the transport of complex polyhedrons, rough objects, and soft, delicate, slippery biological samples.

Electrically switched underwater capillary adhesion

Developing underwater adhesives that can rapidly and reversibly switch the adhesion in wet conditions is important in various industrial and biomedical applications. Despite extensive progresses, the manifestation of underwater adhesion with rapid reversibility remains a big challenge. Here, we report a simple strategy that achieves strong underwater adhesion between two surfaces as well as rapid and reversible detachment in on-demand manner. Our approach leverages on the design of patterned hybrid wettability on surfaces that selectively creates a spatially confined integral air shell to preserve the water bridge in underwater environment. The overall adhesion strength can be multiplied by introducing multiple air shells and rapidly broken by disturbing the integrity of the protective air shell in response to the applied voltage on two surfaces. Our design can be constructed on the flexible substrate with hybrid wettability, which can be applied to non-conductive substrates and adapted to more complicated morphologies, extending the choice of underlying materials.

Strong and bioactive bioinspired biomaterials, next generation of bone adhesives

The bone adhesive is a clinical requirement for complicated bone fractures always articulated by surgeons. Applying glue is a quick and easy way to fix broken bones. Adhesives, unlike conventional fixation methods such as wires and sutures, improve healing conditions and reduce postoperative pain by creating a complete connection at the fractured joint. Despite many efforts in the field of bone adhesives, the creation of a successful adhesive with robust adhesion and appropriate bioactivity for the treatment of bone fractures is still in its infancy. Because of the resemblance of the body's humid environment to the underwater environment, in the latest decades, researchers have pursued inspiration from nature to develop strong bioactive adhesives for bone tissue. The aim of this review article is to discuss the recent state of the art in bone adhesives with a specific focus on biomimetic adhesives, their action mechanisms, and upcoming perspective. Firstly, the adhesive biomaterials with specific affinity to bone tissue are introduced and their rational design is studied. Consequently, various types of synthetic and natural bioadhesives for bone tissue are comprehensively overviewed. Then, bioinspired-adhesives are described, highlighting relevant structures and examples of biomimetic adhesives mainly made of DOPA and the complex coacervates inspired by proteins secreted in mussel and sandcastle worms, respectively. Finally, this article overviews the challenges of the current bioadhesives and the future research for the improvement of the properties of biomimetic adhesives for use as bone adhesives.

Stimuli-responsive temporary adhesives: enabling debonding on demand through strategic molecular design

Stimuli-responsive temporary adhesives constitute a rapidly developing class of materials defined by the modulation of adhesion upon exposure to an external stimulus or stimuli. Engineering these materials to shift between two characteristic properties, strong adhesion and facile debonding, can be achieved through design strategies that target molecular functionalities. This perspective reviews the recent design and development of these materials, with a focus on the different stimuli that may initiate debonding. These stimuli include UV light, thermal energy, chemical triggers, and other potential triggers, such as mechanical force, sublimation, electromagnetism. The conclusion discusses the fundamental value of systematic investigations of the structure-property relationships within these materials and opportunities for unlocking novel functionalities in future versions of adhesives.