image: (a) The adhesive fibril is made of SMPs with switchable material between the soft rubber-phase and stiff glass-phase, and the fibril radius is designed so that the adhesion regime is in the JKR-like mode with weak adhesion and DMT-like mode with strong adhesion. The JKR-DMT transition is enabled by on-demand switching of the material phases through heating. (b) Demonstrations of utilizing the SMP R2G fibrillar adhesive hooks to support various heavy loads. (c) On-demand detachment of the adhesive hook using a hair dryer. (d) Overall comparison of the new SMP fibrillar adhesives compared to the gecko and gecko-inspired ones.
Credit: ©Science China Press
This study is led by Prof. K. Jimmy Hsia (School of Mechanical & Aerospace Engineering, Nanyang Technological University), Prof. Huajian Gao (Mechano-X Institute, Applied Mechanics Laboratory, Department of Engineering Mechanics, Tsinghua University) and their Ph.D. student Dr. Changhong LINGHU (now a research fellow, School of Mechanical & Aerospace Engineering, Nanyang Technological University).
Have you ever wondered how geckos effortlessly climb walls and ceilings? The secret lies in their tiny, hair-like structures on their feet called adhesive fibrils. These natural wonders have inspired scientists to create smart fibrillar adhesives that can stick and unstick on demand, opening up a world of possibilities in robotics, wearable devices, manufacturing, and even medicine.
But mimicking the gecko’s adhesive prowess has been a sticky challenge. Traditional gecko-inspired fibrillar adhesives often struggle with a tug-of-war between stickiness and switchability - the stronger they stick, the harder they are to detach. Plus, as the size of the adhesive fibrils gets bigger, their sticking power weakens, limiting them to tiny scales that are tricky to manufacture. When arranged in arrays, these fibrils also don’t cooperate well, leading to uneven load distribution and limited scaling efficiency.
Enter a groundbreaking new design paradigm that’s taking smart adhesives to the next level. By leveraging a clever phase-changing mechanism in shape memory polymers, researchers have created fibrillar adhesives with mind-blowing strength (think 2 mega Pascals!), exceptional switchability (toggling over 2000 times), and the ability to scale up to millimeter sizes. When arranged in arrays, these adhesives can achieve scaling efficiencies of nearly 57% and support objects weighing a whopping 2000 times their own weight.
The key to this adhesive revolution lies in finding the sweet spot for fibril size, striking a balance between two adhesion regimes - the DMT regime for maximum stickiness and the JKR regime with weak adhesion for easy detachment. By carefully tuning the fibril radius and harnessing the unique properties of shape memory polymers, scientists have pushed the limits of the DMT regime to an unprecedented 2.7 millimeters.
Smart adhesive fibrils at the macroscale, in stark contrast to their micro/nano counterparts, offer significant advantages by dramatically simplifying the fabrication process. Previously, only specialists could create gecko-inspired fibrillar adhesives in the laboratory using sophisticated equipment. Now, with this new design paradigm, these smart adhesives can be easily produced even in a household setting, making this cutting-edge technology accessible to a wider audience and paving the way for innovative applications across various fields.
This breakthrough marks a significant leap forward in our understanding of fibrillar adhesion and opens up a world of possibilities for smart adhesive technology. By breaking free from the constraints of gecko-inspired designs, these innovative adhesives are poised to transform industries from robotics to manufacturing, enabling everything from wall-climbing robots to heavy-duty industrial grippers.
As we continue to explore the frontiers of smart adhesion, the future looks bright for a new generation of adhesive technologies that can stick, switch, and scale like never before. So, the next time you see a gecko scampering up a wall, remember the amazing science that’s bringing, and even transcend their sticky secrets to life in the world of smart adhesives.
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See the article:
Fibrillar adhesives with unprecedented adhesion strength, switchability and scalability https://doi.org/10.1093/nsr/nwae106
Journal
National Science Review