Easy Detachment Research Articles

Self‐Adhesive, Detach‐on‐Demand, and Waterproof Hydrophobic Electronic Skins with Customized Functionality and Wearability

AbstractThe interfacial design of the electronic skins (E‐skins), which are increasingly crucial in areas like exercise monitoring, healthcare, etc., has a great impact on wearability and functions. The adhesion between E‐skin and human skin serves as the foundation for various functionalities. In addition to robust adhesion strength, detaching‐on‐demand, and waterproof abilities are also important for long‐time wearing and comfort detachment after use. Here, self‐adhesive, detach‐on‐demand, and waterproof hydrophobic E‐skins (PBIA) by copolymerization of acrylates with conductive ionic liquid and adhesive components as the strain sensor and triboelectric nanogenerator (TENG) is developed. The strong van der Waals self‐adhesion (shear adhesion of ≈574 kPa, peeling adhesion of ≈110 N m−1), and waterproof abilities under immersing, flushing, and penetrating situations enable the E‐skin to realize stable and long‐time monitoring for body motions in both the resistance sensing and TENG modes. Meanwhile, the easy detach‐on‐demand ability of van der Waals adhesion (574 to 35 kPa and 110 to 7 N m−1) guarantees the easy and comfortable detachment of PBIA after use, avoiding pain or injury to the skin. The adhesion strategy of PBIA can be expanded to other kinds of E‐skins and accelerate the pace of practical applications of E‐skins.

Superhydrophilic and Antifriction Thin Hydrogel Formed under Mild Conditions for Medical Bare Metal Guide Wires.

Medical guide wires play a crucial role in the process of intravascular interventional therapy. However, it is essential for bare metal guide wires to possess both hydrophilic lubricity and coating durability, avoiding tissue damage caused by friction inside the blood vessel during the interventional procedure. Additionally, it is still a huge challenge for diverse metal materials to bind with polymer coatings easily. Herein, we present a hydrogel coating scheme and its preparation method for various wires under mild conditions for environmental protection purposes. The preparation process involves surface pretreatment, including low-temperature heating and silanization, followed by a two-step dip coating and ultraviolet polymerization. The whole process leads to the formation of an interpenetrating cross-linked hydrogel network from the substrate to the surface section. This study confirms the superhydrophilicity and lubricity of three metal wires with the designed coating, especially reducing the friction significantly by ≥ 95%. The thin coating (average thickness <6.2 μm) demonstrates strong adhesion with various substrates and exhibits resistance to 25 or even 125 cycles of friction, indicating excellent stability and preventing easy detachment. The finally prepared composite nickel-titanium (NiTi) guide wire with stainless steel (SS) and platinum-tungsten (Pt-W) coils (overall diameter of ∼0.36 mm) shows satisfactory performance with a friction of 0.183 N for 25 cycles, meeting the clinical requirements (average friction ≤0.2 N) for interventional operation. These findings highlight the potential of this study in advancing the development of medical devices, particularly in the field of intravascular interventional therapy.

Vacuum-powered soft actuator with oblique air chambers for easy detachment of artificial dry adhesive by coupled contraction and twisting

ABSTRACT A gecko foot-inspired, mushroom-shaped artificial dry adhesive exploiting intermolecular forces between microstructure and surface has drawn research attention for its strong adhesive force. However, the high pull-off strength corresponding to the adhesive force matters when detaching fragile substrates. In this study, we report a vacuum-powered soft actuator having oblique air chambers and a dry adhesive. The soft actuator performs coupled contraction and twisting by applying negative pneumatic pressure inward and exhibits not only high pull-off strength but also easy detachment. This effective detachment can be achieved thanks to the twisting motion of the soft actuator. The detachment performances of the actuator models are assessed using a 6-degrees-of-freedom robot arm. Results show that the soft actuators exhibit remarkable pull-off strength decrement from ~20 N cm−2 to ~2 N cm−2 due to the twisting. Finally, to verify a feasible application of this study, we utilize the inherent compliance of the actuators and introduce a glass transfer system for which a glass substrate on a slope is gripped by the flexibility of the soft actuators and delivered to the destination without any fracture.

Switchable shape memory polymer bio-inspired adhesive and its application for unmanned aerial vehicle landing

Controlled and switchable adhesion is commonly observed in biological systems. In recent years, many scholars have focused on making switchable bio-inspired adhesives. However, making a bio-inspired adhesive with high adhesion performance and excellent dynamic switching properties is still a challenge. A Shape Memory Polymer Bio-inspired Adhesive (SMPBA) was successfully developed, well realizing high adhesion (about 337 kPa), relatively low preload (about 90 kPa), high adhesion-to-preload ratio (about 3.74), high switching ratio (about 6.74), and easy detachment, which are attributed to the controlled modulus and contact area by regulating temperature and the Shape Memory Effect (SME). Furthermore, SMPBA exhibits adhesion strength of 80–337 kPa on various surfaces (silicon, iron, and aluminum) with different roughness (Ra = 0.021–10.280) because of the conformal contact, reflecting outstanding surface adaptability. The finite element analysis verifies the bending ability under different temperatures, while the adhesion model analyzes the influence of preload on contact area and adhesion. Furthermore, an Unmanned Aerial Vehicle (UAV) landing device with SMPBA was designed and manufactured to achieve UAV landing on and detaching from various surfaces. This study provides a novel switchable bio-inspired adhesive and UAV landing method.

Development of κ-carrageenan-PEG/lecithin bioactive hydrogel membranes for antibacterial adhesion and painless detachment

The issue of wound dressing adherence poses a substantial challenge in the field of wound care, with implications both clinically and economically. Overcoming this challenge requires the development of a hydrogel dressing that enables painless removal without causing any secondary damage. However, addressing this issue still remains a significant challenge that requires attention and further exploration. The present study is focused on the synthesis of hydrogel membranes based on κ-carrageenan (CG), polyethylene glycol (PEG), and soy lecithin (LC), which can provide superior antioxidant and antibacterial attachment properties with a tissue anti adhesion activity for allowing an easy removability without causing secondary damage. The (CG-PEG)/LC mass ratio was varied to fabricate hydrogel membranes via a facile approach of physical blending and solution casting. The physicochemical properties of (CG-PEG)/LC hydrogel membranes were studied by scanning electron microscopy (SEM), Fourier transforms infrared spectroscopy (FTIR), X-ray diffraction (XRD), differential scanning calorimetry (DSC), and mechanical analyses. The membranes showed significantly enhanced mechanical properties with excellent flexibility and had high swelling capacity (˃1000 %), which would provide a moist condition for wound healing. The membranes also exhibited excellent free radical scavenging ability (>60 %). In addition, the (CG-PEG)/LC hydrogel membranes showed reduced peel strength 26.5 N/m as a result of weakening the hydrogel-gelatin interface during an in vitro gelatin peeling test. Moreover, the membrane showed superior antibacterial adhesion activity (>90 %) against both S. aureus and E. coli due to the presence of both PEG and LC. The results also suggested that the hydrogel membranes exhibit NIH3T3 cell antiadhesion property, making them promising material for easy detachment from the healed tissue without causing secondary damage. Thus, this novel combination of (CG-PEG)/LC hydrogel membranes have immense application potential as a biomaterial in the healthcare sector.

Thermoreversible Tissue Adhesion with Hydrogel Through a Topological Entanglement Approach.

Achieving thermoreversible adhesion between hydrogel and living tissues in a facile way is challenging. Existing strategies bring difficulty to the chemical design and synthesis of hydrogels. Herein, an approach to achieve tough thermoreversible tissue adhesion with hydrogel is proposed, which uses a polymer solution with heat-induced sol-gel transition as the interfacial polymer matrix, with no chemical design required for the hydrogel network. When the interfacial polymer matrix is introduced to the interface of the hydrogel and living tissues, it can gelate in situ within the substrate networks under a temperature stimulus, and topologically entangle with the preexisting networks of the substrates, which generates a strong adhesion. By triggering with another temperature stimulus, the newly formed network dissociates to realize an easy detachment. Thermoreversible adhesion is demonstrated between polyacrylamide hydrogel and various porcine tissues as examples, and the mechanism of this adhesion strategy is studied by varying various influence factors. A theoretical model that can fit and predict the effects of different parameters on the adhesion energies is also established. This adhesion strategy based on topological entanglement among a thermoreversible polymer system and the substrates may broaden the achieving methods of thermoreversible tissue adhesion.

Easy Cell Detachment and Spheroid Formation of Induced Pluripotent Stem Cells Using Two-Dimensional Colloidal Arrays

Induced pluripotent stem cells (iPSCs) may develop into any form of cell and are being intensively investigated. The influence on iPSCs of nanostructures generated using two-dimensional colloidal arrays was examined in this study. Colloidal arrays were formed using the following procedure. First, core–shell colloids were adsorbed onto a glass substrate using a layer-by-layer method. Second, the colloids were immobilized via thermal fusion. Third, the surface of the colloids was modified by plasma treatment. By adjusting the number density of colloids, cultured iPSCs were easily detached from the substrate without manual cell scraping. In addition to planar culture, cell aggregation of iPSCs attached to the substrate was achieved by combining hydrophilic surface patterning on the colloidal array. Multilayered cell aggregates with approximately four layers were able be cultured. These findings imply that colloidal arrays might be an effective tool for controlling the strength of cell adhesion.

Robust and functional polyamide 11 tubular product featuring helical flow-regulated interpenetrating configuration of carbon nanofiber

Miniaturized functional tubular product (MFTP) as a pivotal block of the potable smart devices has been widely applied in advanced industries, however, conventionally-extruded tube often suffers from easy detachment of head-to-end contracting points and weak mechanical reliability along normal direction. Herein, we proposed a facile strategy to prepare polyamide 11 tubular product with a helically-interpenetrating network by manipulating reversed helical flow in rotation extrusion. Compared to the axially-align configuration in conventionally-extruded tube featuring unidirectional reinforcement and easy-disconnecting head-to-end configuration, the helically-interpenetrating CNF network shared similar characteristic to the tracheid-like helical structure existing in wood, providing the composite tube with robust mechanical properties in all directions, but also boosting the initial conductivity and electrical stability under mechanical deformation. With the benefits of outstanding capabilities of robust performance and excellent conductive property, the as-prepared tubular product can be endowed with some special functions including excellent antistatic and electrothermal properties, guaranteeing the safe application in low temperature, vibration environment as a hydraulic brake tube. The helically flow-driven melt-processing was featured with low cost, high efficiency and suitable for continuous industrial fabrication, opening up a facile and effective strategy to prepare excellent MFTP with the hollow and thin wall.

All-in-One Configured Flexible Supercapacitor for Wide-Temperature Operation and Integrated Application

The advantages of stretchable supercapacitors (SCs), such as fast charging and discharging speed, high power density, and long cycle life, have attracted the research interest of many researchers. However, conventional SCs have limited applications in energy storage devices due to their unsatisfactory environmental tolerance, easy detachment of electrodes and electrolytes, and poor stretchability. In this work, a poly(vinyl alcohol) (PVA)–(acrylic acid) (AA) double-network hydrogel electrolyte was prepared by a one-pot method, followed by in situ polymerization of aniline (PANI) to fabricate all-in-one polyaniline SCs (PANI-SCs) devices. Multiple hydrogen bonds and in situ polymerization of PANI and dimethyl sulfoxide (DMSO) endow the PANI-SCs integrated, flexible SCs with good mechanical properties and electrochemical performance in a wide temperature range. The PANI-SCs device exhibits an excellent tensile elongation strain of 413.7% and a mechanical strength of 137.1 kPa. At room temperature, the areal capacitance of the PANI-SCs device is 48.1 mF cm–2. PANI-SCs contains a DMSO component; DMSO lowers the saturated vapor pressure of water to lower its freezing point and suppress the formation of ice crystallites and exhibits normal electrochemical performance over a wide temperature range of −80 to 100 °C. PANI-SCs drive LED lights and integrate with sensors for human health monitoring applications. Potential applications extend the development of flexible SCs in wearable electronics.

Overcoming the adhesion paradox and switchability conflict on rough surfaces with shape-memory polymers

Smart adhesives that can be applied and removed on demand play an important role in modern life and manufacturing. However, current smart adhesives made of elastomers suffer from the long-standing challenges of the adhesion paradox (rapid decrease in adhesion strength on rough surfaces despite adhesive molecular interactions) and the switchability conflict (trade-off between adhesion strength and easy detachment). Here, we report the use of shape-memory polymers (SMPs) to overcome the adhesion paradox and switchability conflict on rough surfaces. Utilizing the rubbery-glassy phase transition in SMPs, we demonstrate, through mechanical testing and mechanics modeling, that the conformal contact in the rubbery state followed by the shape-locking effect in the glassy state results in the so-called rubber-to-glass (R2G) adhesion (defined as making contact in the rubbery state to a certain indentation depth followed by detachment in the glassy state), with extraordinary adhesion strength (>1 MPa) proportional to the true surface area of a rough surface, overcoming the classic adhesion paradox. Furthermore, upon transitioning back to the rubbery state, the SMP adhesives can detach easily due to the shape-memory effect, leading to a simultaneous improvement in adhesion switchability (up to 103, defined as the ratio of the SMP R2G adhesion to its rubbery-state adhesion) as the surface roughness increases. The working principle and the mechanics model of R2G adhesion provide guidelines for developing stronger and more switchable adhesives adaptable to rough surfaces, thereby enhancing the capabilities of smart adhesives, and impacting various fields such as adhesive grippers and climbing robots.

A Spiny Climbing Robot with Dual-Rail Mechanism.

Easy detachment is as important as reliable an attachment to climbing robots in achieving stable climbing on vertical surfaces. To deal with the difficulty of detachment occurring in wheeled and track-type climbing robots using bio-inspired spines, a novel climbing robot utilizing spiny track and dual-rail mechanism is proposed in this paper. The spiny track consists of dozens of spiny feet, and the movement of each spiny foot is guided by the specially designed dual-rail mechanism to achieve reliable attachment and easy detachment. First, the design of the climbing robot and the dual-rail mechanism are presented. Then, the dual-rail model is constructed to analyze the attaching and detaching movements of the spiny feet, and a mechanical model is established to analyze the force distribution on the spiny track. Finally, a robot prototype is developed, and the analysis results are verified by the experiment results. Experiments on the prototype demonstrated that it could climb on various rough vertical surfaces at a speed of 36 mm/s, including sandpaper, brick surfaces, concrete walls with pebbles, and coarse stucco walls.

Design and Control of a Novel Detachable Driving Module for Electrification of Manual Wheelchairs

We developed a detachable electric module that converts a manual wheelchair into an electric wheelchair. The existing electric module requires several parts to be fastened to the wheelchair, which complicates its assembly. In addition, because the overall size of the wheelchair increases after its assembly and the turning radius increases compared to the manual wheelchair, controlling the wheelchair becomes difficult for the user. To compensate for these shortcomings, a new type of electric module composed of two omni-wheel driving units is proposed in this study. Because the two modules can independently move forward or backward and change directions, the same movement as that of the existing manual wheelchair is possible. In addition, a mechanism for easy attachment and detachment is proposed and its versatility is verified by mounting it on various wheelchairs. For the stable operation of the module, field-oriented control was applied, and the wheelchair was controlled for stably moving against external forces and ground disturbances according to the module mounting location. A driving test was conducted according to the mounting location of the developed module, and the proposed driving module and applied algorithm were verified through statistical analysis.

A mechanical adhesive gripper inspired by beetle claw for a rock climbing robot

Rock climbing robots have wide application prospects in field operations and planetary exploration. Herein, a spiny gripper inspired by the beetle (Coleoptera) claw is developed, which can accomplish easy attachment, detachment and good compliance on irregular rough surfaces without complex controls. The attachment probabilities of various microspine layouts are simulated to determine the optimal design parameters for the spine tile. By referencing the structure and attachment process of the beetle claw, a spiny gripper with four bioinspired branches is designed to enable adaptive attachment and smooth detachment. The gripper employs a novel drivetrain hybridized with passive torsion springs and active tendons driven by an ingenious winch to achieve light weight, load-sharing, self-adaptation, and strong adhesion on irregular rough surfaces. The grasp sequence, grasp wrench and gripper maximum adhesion are all investigated. Tests on various surfaces verify its excellent performance. With a weight of 0.352 kg, its normal adhesion and tangential adhesion are 39.7 N and 47.5 N, respectively. In addition, the gripper is integrated into the climbing robot RockClimbo to allow it to move on extreme terrain.

Mechanisms of detachment in fibrillar adhesive systems

Several creatures can climb on smooth surfaces with the help of hairy adhesive pads on their legs. A rapid change from strong attachment to effortless detachment of the leg is enabled by the asymmetric geometry of the tarsal hairs. In this study, we propose mechanisms by which the hairy pad can be easily detached, even when the hairs possess no asymmetry. Here, we examine the possible function of the tibia-tarsus leg joint and the claws. Based on a spring-based model, we consider three modes of detachment: vertically pulling the pad while maintaining either a (1) fixed or a (2) free joint, or by (3) flexing the pad about the claw. We show that in all cases, the adhesion force can be significantly reduced due to elastic forces when the hairs deform non-uniformly across the array. Our proposed model illustrates the design advantage of such fibrillar adhesive systems, that not only provide strong adhesion, but also allow easy detachment, making them suitable as organs for fast locomotion and reliable hold. The presented approaches can be potentially used to switch the adhesion state in bio-inspired fibrillar adhesives, by incorporating artificial joints and claws into their design, without the need of asymmetric or stimuli-responsive fibrillar structures.

Design of a Variable Stiffness Gecko-Inspired Foot and Adhesion Performance Test on Flexible Surface.

Adhesion robots have broad application prospects in the field of spacecraft inspection, repair, and maintenance, but the stable adhesion and climbing on the flexible surface covering the spacecraft has not been achieved. The flexible surface is easily deformed when subjected to external force, which makes it difficult to ensure a sufficient contact area and then detach from it. To achieve stable attachment and easy detachment on the flexible surface under microgravity, an adhesion model is established based on the applied adhesive material, and the relationship between peeling force and the rigidity of the base material, peeling angle, and working surface stiffness is obtained. Combined with the characteristics of variable stiffness structure, the adhesion and detachment force of the foot is asymmetric. Inspired by the adhesion-detachment mechanism of the foot of the gecko, an active adhesion-detachment control compliant mechanism is designed to achieve the stable attachment and safe detachment of the foot on the flexible surface and to adapt to surfaces with different rigidity. The experimental results indicate that a maximum normal adhesion force of 7.66 N can be generated when fully extended, and the safe detachment is achieved without external force on a flexible surface. Finally, an air floating platform is used to build a microgravity environment, and the crawling experiment of a gecko-inspired robot on a flexible surface under microgravity is completed. The experimental results show that the gecko-inspired foot with variable stiffness can satisfy the requirements of stable crawling on flexible surfaces.

Kirigami-inspired adhesion with high directional asymmetry

Robust adhesion to and effortless removal from various substrates are of great importance to soft adhesives in myriad applications. However, controlled regulation between strong attachment and easy detachment in a same system remains challenging. Herein, we report a kirigami-inspired approach to control adhesion with high directional asymmetry. By inscribing a specially designed labyrinth pattern in an adhesive film, the adhesion is enhanced against peeling along a particular direction – the peak peel force builds up at a much smaller peeling angle, and the adhesion energy climbs through in-plane elastic dissipaters. Such a mechanism is inactive when the adhesive is peeled in the opposite direction, and easy detachment is experienced. The underlying physics is elucidated via theoretical and numerical analyses and verified through experiments by using hydrogel adhesives with different elastic moduli and geometric parameters. The asymmetric adhesion can be further enhanced over soft substrates or by designing hierarchical structures – increases by up to 22 folds in strength and 7 folds in energy have been observed. The proposed mechanism is universally applicable to various intermolecular interactions and different loading modes, and can pave the way to engineering new adhesives with superior yet controllable adhesion performance.

Effects of loading and unloading control parameters on adhesive performance for biomimetic controllable adhesive with wedge-shaped microstructures

The adhesive performance of biomimetic controllable adhesive based on wedge-shaped microstructures is affected by some relevant control parameters in the process of loading and unloading. An appropriate selection of these control parameters is of great significance for its effective application. However, little research has concentratively and comprehensively explored these control parameters. In order to make up for the shortcoming, this study systematically explored the macroscopic adhesive performance of the self-developed wedge-shaped microstructures under different loading and unloading control parameters. The results show that preloading depth and tangential dragging distance have a positive effect on the adhesive performance, while preloading angle and peeling angle have a negative effect on the adhesive performance. Specifically, a low preloading angle can weaken the normal preloading force under the same preloading depth, thereby improving the preloading benefit; the application of tangential dragging distance can also induce the normal preloading force generated in the preloading stage to change the adhesion, so as to stimulate more adhesion. Based on the interactive analysis of these control parameters, it can be sure that applying a moderate normal preloading force and a larger tangential dragging distance to the wedge-shaped microstructures at low preloading angle not only makes the wedge-shaped microstructures possess better adhesive capacity, but also can obtain a good preloading benefit. In addition, the promotion effect of a low peeling angle on the adhesive performance also implies that a higher peeling angle should be used to realize the easy detachment of the adhesive interface. The first concentrative and comprehensive investigation of the relevant control parameters of wedge-shaped microstructures lays the foundation for designing a climbing robot or adhesive gripper based on the wedge-shaped microstructures, and also provides guidance for formulating the corresponding control strategies.

Wafer-Scale Fabrication and Transfer of Porous Silicon Films as Flexible Nanomaterials for Sensing Application.

Flexible sensors are highly advantageous for integration in portable and wearable devices. In this work, we propose and validate a simple strategy to achieve whole wafer-size flexible SERS substrate via a one-step metal-assisted chemical etching (MACE). A pre-patterning Si wafer allows for PSi structures to form in tens of microns areas, and thus enables easy detachment of PSi film pieces from bulk Si substrates. The morphology, porosity, and pore size of PS films can be precisely controlled by varying the etchant concentration, which shows obvious effects on film integrity and wettability. The cracks and self-peeling of Psi films can be achieved by the drying conditions after MACE, enabling transfer of Psi films from Si wafer to any substrates, while maintaining their original properties and vertical alignment. After coating with a thin layer of silver (Ag), the rigid and flexible PSi films before and after transfer both show obvious surface-enhanced Raman scattering (SERS) effect. Moreover, flexible PSi films SERS substrates have been demonstrated with high sensitivity (down to 2.6 × 10−9 g/cm2) for detection of methyl parathion (MPT) residues on a curved apple surface. Such a method provides us with quick and high throughput fabrication of nanostructured materials for sensing, catalysis, and electro-optical applications.

Assembly of Graphene Platelets for Bioinspired, Stimuli-Responsive, Low Ice Adhesion Surfaces.

Design and fabrication of functional materials for anti-icing and deicing attract great attention from both the academic research and industry. Among them, the study of fish-scale-like materials has proved that enabling sequential rupture is an effective approach for weakening the intrinsic interface adhesion. Here, graphene platelets were utilized to construct fish-scale-like surfaces for easy ice detachment. Using a biomimicking arrangement of the graphene platelets, the surfaces were able to alter their structural morphology for the sequential rupture in response to external forces. With different packing densities of graphene platelets, all the surfaces showed universally at least 50% reduction in atomistic tensile ice adhesion strength. Because of the effect of sequential rupture, stronger ice–surface interactions did not lead to an obvious increase in ice adhesion. Interestingly, the high packing density of graphene platelets resulted in stable and reversible surface morphology in cyclic tensile and shearing tests, and subsequently high reproducibility of the sequential rupture mode. The fish-scale-like surfaces built and tested, together with the nanoscale deicing results, provided a close view of ice adhesion mechanics, which can promote future bioinspired, stress-responsive, anti-icing surface designs.

A Tissue Adhesion-Controllable and Biocompatible Small-Scale Hydrogel Adhesive Robot.

Recently, the realization of minimally invasive medical interventions on targeted tissues using wireless small-scale medical robots has received an increasing attention. For effective implementation, such robots should have a strong adhesion capability to biological tissues and at the same time easy controlled detachment should be possible, which has been challenging. To address such issue, a small-scale soft robot with octopus-inspired hydrogel adhesive (OHA) is proposed. Hydrogels of different Young's moduli are adapted to achieve a biocompatible adhesive with strong wet adhesion by preventing the collapse of the octopus-inspired patterns during preloading. Introduction of poly(N-isopropylacrylamide) hydrogel for dome-like protuberance structure inside the sucker wall of polyethylene glycol diacrylate hydrogel provides a strong tissue attachment in underwater and at the same time enables easy detachment by temperature changes due to its temperature-dependent volume change property. It is finally demonstrated that the small-scale soft OHA robot can efficiently implement biomedical functions owing to strong adhesion and controllable detachment on biological tissues while operating inside the body. Such robots with repeatable tissue attachment and detachment possibility pave the way for future wireless soft miniature robots with minimally invasive medical interventions.