Controlled Dry Adhesion of Bio-Inspired Fibrillar Polymers: Mechanics, Strategies, and Recent Advances
Abstract
:1. Introduction
2. Interface Mechanics Between Microfibrils and Substrate
2.1. Contact Mechanics and Contact Splitting Efficiency
2.1.1. Pull-Off Force and Peel Force
2.1.2. Contact Splitting Efficiency
2.2. Fracture Mechanics of the Interface Between Microfibrils and Substrate
2.2.1. Total Energy of System and Fiber Deformation Equations
2.2.2. Stress Intensity Factor in Microfibril Arrays and Effective Energy Release Rate
2.2.3. Critical Force Scaling and Predicting Adhesive Behaviors
2.3. Coupled Adhesion and Friction
3. Effective Adhesion Strength of Artificial Fibrillar Adhesives
3.1. Contact Geometry and Stiffness of Microfibrils and Backing Layer
3.2. Substrate Roughness
3.3. Environmental Factors and Pull-Off Dynamics
Research Approaches | Key Methods/Models | Key Research Focus | System Studied | Example Applications |
---|---|---|---|---|
Fracture Mechanics and Numerical Simulations | Linear Elastic Fracture Mechanics (LEFM) [60,61,99,103,115,118,146,147] | Stress distribution, crack initiation and propagation | Single fibril and arrays | Predicting detachment in adhesive systems |
Cohesive Zone Modeling [68,71,72,73,74,107] | Interfacial energy dissipation and failure | Fibril–substrate interface | Enhanced control over detachment mechanics | |
Hybrid Dynamic Fracture Mechanics [101,141,142,143,144,145] | Dynamic adhesion characteristics and rate-dependent work of adhesion | Single-fibril, micropatterned surfaces | Rate effects in synthetic adhesive structures | |
Contact Mechanics | Contact Splitting [24,41], Peeling and Pull- Off [44,63,96,131], Equal Load Sharing [114,146], Traction–Separation Relation [50,100,102] | Load distribution and contact area scaling, enhancing adhesion on rough surfaces, backing-layer | Single fibril or arrays | High-strength adhesion with load-sharing, roughness effects |
Elasticity Models | Spring Models [67,128] | Compliance and load-sharing | Single fibril or arrays | Designing optimal adhesion under loading |
Statistical Models | Weibull Statistics, Probabilistic Models [40,69,70] | Variability in adhesion due to defects | Fibril array | Robust adhesion performance with defects |
Coupled Adhesion and Friction | Frictional Adhesion Modeling [83,85,86,87] | Effects of shear force on adhesion | Arrays | Applications in robotic grippers |
Buckling and Bending Analysis | Analytical or Numerical [48,148] | Stability under compressive loads, self-adhesion | Single fibril or array | Enhanced adaptability to uneven surfaces |
Data-Driven Modeling | Supervised Machine Learning [65,66,117,149] | Prediction of adhesion strength, pattern recognition | Micropatterned surfaces | Performance optimization in adhesion design |
4. Enhancing or Tuning Adhesion: Case Studies
4.1. Innovative Design and Optimization of Fibrillar Adhesives
Design Strategy | Applications | Advantages/Innovations |
---|---|---|
Dry-adhesive microstructure for rough surfaces [7] | Material handling on Mars | 392.94× increase in pull-off stress; enables low-energy handling of rough, additively manufactured surfaces |
Springtail-, gecko-, and octopus-inspired 3D microstructures [153] | Medical devices, robotics, wearable adhesives | Strong reversible adhesion; super-repellency on wet and dry surfaces; versatile for synthetic/biological surfaces |
Mushroom-shaped fibrillar arrays with double re-entrant tips [154] | Robotics, medical devices, underwater adhesives | Retains adhesion in presence of water, oil, and other liquids; robust, stretchable, and highly deformable |
Trapezoidal-prism + mushroom-shaped microstructure [155] | Pick-and-place for microelectronics, transfer printing | Strong adhesion (87.8 kPa); low detachment strength (<0.07 kPa); works in dry and wet conditions |
Gecko-inspired adhesive with spatial variation [156] | Robotics, climbing devices | 100× stronger adhesion in preferred direction; enhances control and mimics natural adhesive asymmetry |
Anisotropic dry-adhesive microstructures produced via two-photon polymerization [157] | Space debris capture, high-anisotropy applications | High anisotropic adhesion factor (7.52:1); strong adhesion (up to 1105.29 mN/cm2); suitable for mass production |
Combined microfibril textures (micro-spatulae and micro-mushroom) [159] | Robotics, adaptive gripping systems | Optimized adhesion and friction under varying loads and velocities; adaptable to environmental conditions |
Off-center spatula-shaped microfiber caps [161] | Pick-and-place, robotics | 3–5× reduction in adhesion for easy detachment; 3× increase in shear with lateral drag; versatile directional control |
Mushroom-like PDMS microline arrays with directional patterns [162] | Silicon wafer transportation | High shear adhesion in parallel direction; low peeling force, enabling easy detachment and directional control |
Elastomeric mushroom-shaped microfibers with PSA layer [163] | Wearable medical devices, transfer printing, robotic manipulation | High adhesion strength (300 kPa); 35× durability improvement on smooth surfaces |
T-shaped PDMS micropillars with modulus gradient [164] | Robotics, gripping systems | 4.6× increase in adhesion; 2.4× increase in friction compared to pure PDMS arrays |
Fiber-reinforced adhesive with bio-inspired soft backings [167] | Soft robotic grippers, curved surfaces | Enhanced conformability and friction on curved substrates; scalable contact area inversely with backing stiffness |
Mushroom-like adhesive pillars with optimized geometry [168] | Robotic grasping, microtransfer printing | 2× adhesion enhancement; reduced edge stress concentration; crack initiation shifted to pillar center |
Machine learning-optimized composite pillars [169] | Robotics, adhesive interfaces | 11× increase in detachment force; high adhesion under varied loading conditions; 1.7× improvement over rectangular core design |
Gecko-inspired micropillars with asymmetrical tilt [170] | Robotics, gripping systems | 4× stronger adhesion than plain surface; 2× stronger in gripping direction than release direction |
Machine learning-optimized gecko-inspired fibrils [171] | Robotics, medical devices | 77% improvement in adhesion; sensitivity to fibril shape and deformation considered |
Free-form optimized adhesive pillar shapes [172] | Robotics, adhesive interfaces | Improved uniformity in stress distribution without stress peaks |
Directional adhesive pillars with anisotropic properties [173] | Wall-climbing robots, grippers | Superior directionality and adhesion strength |
In-plane combination of micropillars with different aspect ratios [175] | Space capture and docking | Maintains 85% adhesion after large deformation; resists overload-induced adhesion failure; adaptable to dynamic capture |
4.2. Strategies of Reversibly Controlled Adhesion and Latest Advances
4.2.1. Controlling the Amount of True Surface Contact
4.2.2. Controlled Adhesion by Shear Force
5. Discussion
5.1. Key Mechanisms and Innovations
5.2. Challenges in Interface Mechanics
5.3. Precision, Repeatability, and Practical Applications
5.4. Expanding the Application Range
6. Conclusions and Outlook
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
References
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Refrigerator | Table Desktop | Sputter Coater | 0.3 μm FibrMet disc | |
---|---|---|---|---|
Rq (μm) | 0.057 | 0.162 | 0.22 | 0.226 |
Pull-off force (mN) (Original/Split) | 42/54.2 | 30/44.5 | 30.1/48.5 | 37/41.8 |
Static friction force (mN) (Original/Split) | 360/398 | 280/374 | 250/308 | 335/310 |
Design Strategy | Control Mechanism | Applications | Advantages/Innovations |
---|---|---|---|
Suction + gecko-inspired adhesion [3] | Suction for grip; nylon fabric with gentle airflow | Retail and warehouse robots | Lifts up to 2.3 kg; grips small items; conforms to irregular surfaces |
Soft–hard–soft sandwiched composite for reversible adhesion [176] | Lateral shrinkage for uniform loading; stress concentration for easy detachment | Precision manufacturing, flexible electronics, climbing robots | Scalable adhesion (1.5 to 150 cm2); supports loads from 20 to 700 N; fast switching (~0.2 s); adhesion switching ratio of ~54 |
Hierarchical bionic toe (bio-toe) with elastic actuator and bionic lamellae [177] | Bi-directional pressure for adhesion/release and non-linear deformation for adaptability | Robot grippers, wall-climbing robots, space, defense | High adaptability and load capacity; 100% release success; 12× shear adhesion force-to-preload ratio; contact rate of 60% even with contact tilt |
Directional buckling micropatterned adhesives [178] | Compressive overload for elastic buckling and controlled release | Pick-and-place systems, micro-assembly | High switching ratio (~20); precise release of objects <1 mm; enhanced placement accuracy |
Double-sided micropatterned PDMS adhesive pads [179] | Elastic buckling instabilities to switch adhesion states | Temporary double-sided fixation, micro-assembly | High switching efficiency (up to 83%); controlled detachment from one side |
Soft hollow pillars (SHPs) with sidewall buckling [181] | Low-pressure control (negative for buckling, positive for bulging) | Microtransfer printing, selective pick-and-place | High adhesion tunability (up to 151×); versatile for varied surface textures and curvatures; low energy cost |
Dry adhesive with multiphalange, multifinger design [182] | Buckling ribs for shear load sharing and normal compliance | Robotic manipulators, flexible grippers | High contact area; efficient shear load distribution; adaptable manipulation beyond pick-and-place |
Multilayer adhesive with backing, middle, and bottom layers [183] | Preload adjustment for rapid adhesion switching via underside buckling | Transportation, handling applications | High switching ratio (up to 136×); rapid switching; dirt-resistant film-terminated structure |
Trigger plant-inspired snap-action metastructure [185] | Tunable spring with snap-through mechanism for adhesion switching | Micro-object handling, pick-and-place systems | Extremely high switching ratio (>10,000); effective in dry/wet and smooth/rough environments |
Mushroom-shaped adhesive with magnetized tip [187] | Magnetic actuation for morphology transformation and adhesion switching | Transfer technology, precision pick-and-place | Rapid and reversible adhesion control; noncontact switching for selective pickup and release |
Gecko-inspired shape-memory polymer (SMP) adhesive [188] | Shape recovery for reversible adhesion switching | Glass transfer systems, precision assembly | High adhesion (≈332.8 kPa) with easy detachment (3.73 kPa); adaptable to various surfaces |
Gecko- and creeper-inspired fibrillar adhesive with PU-GSMP layers [189] | UV-induced photothermal effect for phase change in GSMP micropillars | Robotics, handling rough surfaces | High adhesion strength (278 kPa); high switching ratio (29); fast switching (10 s); adaptable to surfaces with varied roughness |
Hierarchical structure with stiffness modulation [190] | Electrothermal film for adjustable stiffness in TPU layer | Soft grippers, wall-climbing robots | High and switchable adhesion on non-flat surfaces; adhesion increased by 10–100× with voltage control |
Thermally responsive shape-memory polymer with micropillars [191] | Laser heating for shape recovery to switch adhesion | Noncontact transfer printing, electronics assembly | Strong adhesion for pick-up; laser-driven release for noncontact printing; adaptable to diverse surfaces (e.g., sandpaper, glass) |
Superhydrophobic film with shape-memory polyurethane-cellulose nanofiber substrate [192] | Shape-memory effect for switching adhesion states | Controlled droplet manipulation, microfluidics | Captures/releases multiple droplets step-by-step |
Shape-memory polymer (SMP) adhesive gripper [194] | Thermoelectric Peltier module for active heating and cooling to switch adhesion | Robotic pick-and-place, manipulation | Strong grip force (>2 atmospheres); minimal release force; works on flat, rough, and wet surfaces |
Elastomeric 3D surface structures with conductive nanowire electrodes [197] | Combined shear and electrostatic adhesion, capacitive sensing for touch | Soft grippers, tactile sensors | 72% increase in gripping force with voltage; adaptable to various materials; multifunctional for adhesion and force sensing |
Gripper with gecko adhesive and thermo-responsive filament [198] | Hydraulic-driven bending actuators, variable stiffness filament | High-load grasping, soft robotics, industrial handling | 655% increase in holding force; rapid cooling (31 s); cost-effective and scalable fabrication |
Microstructured adhesive with integrated piezoelectric element [199] | Ultrasonic vibration for dust removal and adhesion tuning | Robotics, cleanroom applications | Removes 53–71% of contaminants; recovers 3–11% adhesion post-contamination; maintains performance over 1500 cycles |
Combined electrostatic and gecko-inspired adhesive [200] | Tunable adhesion via electrostatic and microstructured adhesive layers | Grasping diverse materials, soft robotics | 100–168% increased gripping force across various materials; effective on rough surfaces; adaptable for soft and fragile objects |
Hierarchical structure: asymmetric wedges + mushroom fibrils [201] | Loading–dragging–pulling and magnetic field actuation | Flexible devices, releasing ultra-light objects | Dual switchable adhesion modes; overcoming shear-induced adhesion limits; self-cleaning; ultra-light release |
Soft gripper with 3D-printed directional adhesives and curved pillars [202] | Adhesion enhancement via additional coating for smoothness and tip deformation | Handling thin, flexible objects (e.g., films, FPCBs) | Cost-effective; environment-friendly; retains 95% adhesion after 10,000 cycles; adhesion recovery with cleaning |
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© 2025 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).
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Xu, S.; Emami, A.; Khaleghian, M. Controlled Dry Adhesion of Bio-Inspired Fibrillar Polymers: Mechanics, Strategies, and Recent Advances. Materials 2025, 18, 1620. https://doi.org/10.3390/ma18071620
Xu S, Emami A, Khaleghian M. Controlled Dry Adhesion of Bio-Inspired Fibrillar Polymers: Mechanics, Strategies, and Recent Advances. Materials. 2025; 18(7):1620. https://doi.org/10.3390/ma18071620
Chicago/Turabian StyleXu, Shuo, Anahita Emami, and Meysam Khaleghian. 2025. "Controlled Dry Adhesion of Bio-Inspired Fibrillar Polymers: Mechanics, Strategies, and Recent Advances" Materials 18, no. 7: 1620. https://doi.org/10.3390/ma18071620
APA StyleXu, S., Emami, A., & Khaleghian, M. (2025). Controlled Dry Adhesion of Bio-Inspired Fibrillar Polymers: Mechanics, Strategies, and Recent Advances. Materials, 18(7), 1620. https://doi.org/10.3390/ma18071620