Humans twist and turn as a result of intricate physiological processes in which the neurological system of the body communicates our intentions, the musculoskeletal system supports the motion, and the digestive system supplies the necessary energy.
We are not even aware that coordinated, dynamic processes are going place when the body integrates these activities. Few one-component materials naturally possess the spatial and temporal coordination required to duplicate the spontaneity and dexterity of biological behavior, making it challenging to replicate equivalent, integrated functioning in a single synthetic substance.
Researchers from the University of Pittsburgh Swanson School of Engineering and the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have developed a single-material, self-regulating system that can bend and twist in a manner that is biomimetic through a combination of modeling and experiments.
The senior author is Joanna Aizenberg, the Amy Smith Berylson Professor of Materials Science and Professor of Chemistry & Chemical Biology at SEAS. Inspired by experiments performed in the Aizenberg lab, contributing authors at the University of Pittsburgh, Anna Balazs and James Waters developed the theoretical and computational models to design liquid crystal elastomers (LCEs) that imitate the seamless coupling of dynamic processes observed in living systems.
“Our movements occur spontaneously because the human body contains several interconnected structures, and the performance of each structure is highly coordinated in space and time, allowing one event to instigate the behavior in another part of the body,” explained Balazs, Distinguished Professor of Chemical Engineering and the John A. Swanson Chair of Engineering.
“For example, the firing of neurons in the spine triggers a signal that causes a particular muscle to contract; the muscle expands when the neurons have stopped firing, allowing the body to return to its relaxed shape. If we could replicate this level of interlocking, multi-functionality in a synthetic material, we could ultimately devise effective self-regulating, autonomously operating devices.”
The coupling among microscopic units the polymers, side chains, meogens, and crosslinkers within this material could remind you of the interlocking of different components within a human body; suggesting that with the right trigger, the LCE might display rich spatiotemporal behavior.Professor Anna Balazs
Long polymer chains with rod-like groups (mesogens) attached through side branches made up the LCE material employed in this Harvard-Pitt study. Photo-responsive crosslinkers were used to make the LCE material responsive to UV light.
The substance was shaped into micron-scale posts that were fastened to a surface below. The Harvard researchers then displayed a broad range of intricate motions that the microstructures can exhibit in the presence of light.
“The coupling among microscopic units the polymers, side chains, meogens, and crosslinkers within this material could remind you of the interlocking of different components within a human body,” said Balazs, “suggesting that with the right trigger, the LCE might display rich spatiotemporal behavior.”
Waters created a model that captures the simultaneous optical, chemical, and mechanical events occurring over the variety of length and time scales that characterize the LCE in order to provide the most efficient triggers.
Additionally, the simulations provide a useful way to discover and visualize the intricate interactions present in this responsive opto-chemo-mechanical system.
“Our model can accurately predict the spatial and temporal evolution of the posts and reveal how different behaviors can be triggered by varying the materials’ properties and features of the imposed light,” Waters said, further noting
“The model serves as a particularly useful predictive tool when the complexity of the system is increased by, for example, introducing multiple interacting posts, which can be arranged in an essentially infinite number of ways.”
According to Balazs, the development of the next generation of light-responsive, soft machines or robots that start to demonstrate lifelike autonomy is made possible by the combination of modeling and experimental studies.
“Light is a particularly useful stimulus for activating these materials since the light source can be easily moved to instigate motion in different parts of the post or collection of posts,” she said.
In further research, Waters and Balazs will examine how arrays of posts and posts with various geometries respond to the interaction of numerous or more localized light beams.
According to preliminary findings, the LCE posts may imitate the flexibility and mobility of fingers in the presence of multiple light beams, opening up new design possibilities for soft robotic hands that can handle light.
“The vast design space for individual and collective motions is potentially transformative for soft robotics, micro-walkers, sensors, and robust information encryption systems,” said Aizenberg.