Shape-shifting metamaterial inspired by octopuses is a world first

Researchers in South Korea have created for the first time a remarkably codable multifunctional material that can be changed into different shapes and mechanical properties in real time. The inspiration for this new metamaterial came from an unlikely place: octopuses.

According to the researchers, this material exceeds the limits of existing materials and opens up new possibilities for various fields that require rapid adaptability, especially within robotics.

Overcoming the hard limits of soft machines

Compared to biological examples, soft machines tend to lag behind in their ability to adapt to the ever-changing environment. This is because there are significant limitations on their real-time tuning, as well as limitations on the range of their reprogrammable features and functionalities. That is, until now.

The new digitally programmable material has several remarkable mechanical capabilities, including shape change and memory, stress-strain responses, and the Poisson’s ratio (which shows how the cross-sectional area of ​​a deformable body changes with longitudinal stretching) under compressive loading.

Furthermore, the new material demonstrates application-oriented functionalities, such as adjustable and reusable energy absorption and pressure release.

The breakthrough could herald a new era of development for fully adaptive soft robots and smart interactive machines.

“We have introduced a metamaterial composite system that enables gradual and reversible adjustments in different mechanical information by translating encoded digital pattern information into discrete stiffness states of the mechanical pixels,” the team writes in their paper.

To develop it, the team led by Professor Jiyun Kim from the Department of Materials Science and Engineering at UNIST, South Korea, introduced a new approach using graphical stiffness patterns, which enable rich shape reconfigurability of a material. This allowed them to independently switch between what they call the ‘digital binary stiffness states’ (basically soft or stiff states) of the material’s constituent units, within a ‘simple auxetic’ (a structure or material with a negative Poisson’s ratio) with therein elliptical cavities.

The material, the authors explain in their paper, achieves “in situ and gradational tuning in different mechanical qualities.”

“We have developed a metamaterial that can implement the desired features in minutes, without the need for additional hardware,” said Jun Kyu Choe, first author of the study and a student in Materials Science’s combined MS/PhD program and Engineering at UNIST, said in a statement.

“This opens up new possibilities for advanced adaptive materials and the future development of adaptive robots.”

Choe and colleagues demonstrated the material’s potential through an “adaptive shock energy-absorbing material,” which adjusts its properties in response to sudden shocks. The material was able to reduce the risk of damage or injury by minimizing the force transmitted to the protected object. The team then turned the material into a “power transmission material,” which delivered force at desired locations and times.

diagram showing different pixel patterns in the material and how they affect pressure absorption when an iron ball is dropped on it

Changing the pattern of activated pixels in the material affects how it responds in a ball-drop experiment.

Image credit: UNIST (cropped)

By entering specific digital commands, the material can control adjacent LED switches, allowing precise control over the power transfer paths.

The metamaterial is also compatible with a range of existing devices and gadgets, as well as artificial intelligence technologies, including deep learning.

“This metamaterial, capable of converting digital information into physical information in real time, will pave the way for innovative new materials that can learn and adapt to their environments,” said Professor Kim.

The research has been published in Advanced Materials.

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