Bioinspired MXene-cellulose nanofiber actuator design mimics plant movement

(Nanowerk Spotlight) In a significant breakthrough, a team of researchers from China and Singapore has developed a bioinspired dynamic matrix of soft actuators that integrates sensing and actuation functions in a single material system. Drawing inspiration from the intelligent sensing and movement of plants like mimosa, the researchers combined the unique properties of MXene and cellulose nanofibers (CNF) to create a soft actuator that can detect touch and rapidly respond with localized movement.
The findings have been reported in Advanced Functional Materials ("Bioinspired Dynamic Matrix Based on Developable Structure of MXene-Cellulose Nanofibers (CNF) Soft Actuators").
The integration of sensing and actuation capabilities in a single material system has been a long-standing challenge in the field of soft robotics. Conventional soft actuators often rely on separate components for sensing and actuation, leading to complex designs and limited responsiveness. By leveraging the multifunctional properties of advanced nanomaterials like MXene and CNF, the researchers have overcome this hurdle, paving the way for truly biomimetic soft actuators.
MXene, a class of two-dimensional transition metal carbides and nitrides, has garnered significant attention in recent years due to its exceptional electrical and thermal conductivity, mechanical strength, and dispersibility in water. However, pure MXene films often suffer from brittleness and limited strain range, hindering their application in soft actuators. To address this issue, the researchers incorporated CNF, a sustainable and bio-derived nanomaterial with excellent mechanical properties and hydrophilicity, into the MXene matrix.
The resulting MXene-CNF composite exhibited a remarkable six-fold improvement in strain range compared to pure MXene films, achieving a working strain of approximately 14%. This enhancement in flexibility and strain tolerance is crucial for developing soft actuators that can undergo large deformations without failure. However, it is important to note that the scalability and cost-effectiveness of producing MXene-CNF composites remain challenges that need to be addressed for widespread adoption.
A biomimetic dynamic matrix with intelligent proprioceptive and instant feedback capability
A biomimetic dynamic matrix with intelligent proprioceptive and instant feedback capability. a) The working mechanism of a mimosa plant, transitioning from its open stage to closed stage when exposed to external stimulation. b) Schematic illustrations of the structure of the biomimetic intelligent dynamic matrix, with each actuator consisting of both soft actuator and flexible triboelectric sensor layer: each element in matrix represents a different leaf of mimosa plant, with a triboelectric tactile sensor in each element imitating the action potential induced by the stimuli on the mimosa plant to sense instantaneous stimuli, which further converts the mechanical stimuli into electrical signals to trigger the location identification and rapid actuating of the soft actuator. MXene-CNF serves as both the photothermal conversion layer and triboelectric sensing layer. (Reprinted with permission by Wiley-VCH Verlag)
The researchers fabricated a series of soft actuators using a bilayer structure, with the MXene-CNF composite serving as the active layer and a passive elastomer layer made of polydimethylsiloxane (PDMS). When exposed to near-infrared light, the MXene-CNF layer efficiently converts the energy into heat, causing the actuator to bend and deform due to the mismatch in thermal expansion between the two layers. This photothermal actuation mechanism enables remote, wireless control of the actuators, offering flexibility in designing responsive systems.
One of the key innovations in this work is the seamless integration of a triboelectric sensing function directly into the MXene-CNF layer. Triboelectric sensors generate electrical signals when two dissimilar materials come into contact and separate, allowing for highly sensitive detection of touch and pressure. By using the MXene-CNF layer as both the actuating and sensing element, the researchers achieved a remarkably low touch detection limit of just 0.3 kPa, surpassing many previously reported triboelectric sensors. Moreover, the actuators demonstrated rapid response times of 90 milliseconds, enabling near-instantaneous feedback to stimuli.
To showcase the potential of this technology, the researchers constructed a dynamic matrix composed of multiple MXene-CNF actuators arranged in a 3x3 array, inspired by the structure and behavior of mimosa leaves. This matrix exhibited intelligent proprioception and instant feedback capabilities, closely mimicking the rapid, spatially precise folding of mimosa leaves in response to touch. When a single actuator in the matrix was touched, it quickly identified the location of the stimulus and triggered a localized response, with the activated actuator bending while the others remained unaffected.
The development of this bioinspired dynamic matrix of MXene-CNF actuators represents a significant advancement in the field of soft robotics and intelligent materials. By seamlessly integrating actuation, sensing, and control functions into a single, flexible platform, this approach opens up exciting possibilities for creating truly biomimetic systems that can adapt and respond to their environment with the sophistication and efficiency of living organisms.
Potential applications for this technology span a wide range, from adaptive robotic grippers and intelligent prosthetics to responsive camouflage and interactive interfaces. The ability to precisely detect and localize touch stimuli while rapidly triggering actuation could enable soft robots to navigate complex environments, handle delicate objects, and interact safely with humans. In biomedical contexts, such actuators could be used to create smart bandages or implants that can sense and respond to changes in pressure, temperature, or chemical composition.
However, it is essential to recognize the current limitations and challenges in translating this technology into practical applications. Scalability, cost-effectiveness, and long-term stability are among the key hurdles that need to be addressed. Further research is needed to optimize the fabrication processes, explore alternative materials, and investigate the performance of these actuators in real-world scenarios.
Despite these challenges, the bioinspired dynamic matrix of MXene-CNF actuators developed by this research team represents a significant leap forward in the quest to create truly biomimetic soft robots and intelligent systems. As scientists continue to draw inspiration from the natural world and push the boundaries of materials science and engineering, we can anticipate even more remarkable advances in this field.
The integration of sensing and actuation functions in a single material system, as demonstrated by this work, opens up new avenues for designing responsive, adaptable, and intelligent soft robots. With further refinement and scale-up of these techniques, we may soon witness the emergence of soft robotic systems that can sense, learn, and interact with their environment in ways that were once thought to be exclusive to biological organisms. This research brings us one step closer to realizing the vision of truly lifelike artificial systems that can mimic the extraordinary abilities of plants and animals.
Michael Berger By – Michael is author of three books by the Royal Society of Chemistry:
Nano-Society: Pushing the Boundaries of Technology,
Nanotechnology: The Future is Tiny, and
Nanoengineering: The Skills and Tools Making Technology Invisible
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