Researchers at North Carolina State University have developed a polymer structure inspired by traditional Chinese lanterns that can transform into more than a dozen distinct, stable shapes. This innovation in material science creates a foundation for a new class of devices that can change their form and function on command. The structure, which can be manipulated by compression, twisting, or even a remote magnetic field, has the potential to be used in a wide array of applications, from biomedical devices to robotics and aerospace engineering.
The core of this new technology lies in the principles of bistability and multistability, which allow the material to hold a specific shape without needing a constant input of energy. By engineering a simple sheet of polymer with a series of precise cuts, the research team has created a device that can store and release energy to rapidly snap between its various configurations. This breakthrough paves the way for the development of adaptive materials that can respond to their environment or be controlled remotely to perform complex tasks, opening up new possibilities in fields that require lightweight, reconfigurable structures.
A Design Inspired by Tradition
The fundamental design of this shape-shifting material is elegantly simple, drawing its inspiration from the collapsible form of a paper lantern. The researchers begin with a flat, parallelogram-shaped sheet of a polymer. Across the center of this sheet, they cut a series of parallel lines, creating a flexible core of interconnected ribbons. The top and bottom of the sheet are left as solid strips, which provide structural integrity. When the left and right edges of this incised sheet are connected, the structure naturally forms a shape that closely resembles a traditional Chinese lantern.
This initial lantern shape is the foundation for the material’s transformative properties. The choice of a lantern as a model was not purely aesthetic; its geometry is key to the way the structure deforms under pressure. The parallel slits allow the material to bend and fold in predictable ways, while the solid strips at the top and bottom act as anchor points, guiding the transformation. This careful balance of flexible and rigid components is what allows the structure to transition between its various stable states, a process that is both rapid and repeatable. The design is a testament to how traditional craft and modern engineering can intersect to produce novel technological solutions.
The Science of Shape-Shifting
The ability of the lantern structure to change its shape is rooted in the scientific principles of bistability and multistability. A bistable system is one that has two different stable states. In the case of the lantern, its initial, expanded shape is one stable state. When a compressive force is applied from the top, the structure begins to deform, storing the energy from the compression. As the pressure increases, the lantern reaches a critical point and then rapidly snaps into a second stable shape, which resembles a spinning top. In this compressed state, the structure is also stable and will hold its form without any external force being applied. The energy used to compress it is stored within the material itself.
This stored energy is what allows the structure to quickly revert to its original form. When the compressive force is released and a slight upward pull is applied, the stored energy is released all at once, causing the structure to snap back into its lantern shape with remarkable speed. This rapid, reversible transformation between two stable states is the essence of its bistable nature. The researchers have effectively created a mechanical switch, one that can be toggled between two distinct shapes, each with its own unique properties and potential uses. The efficiency of this energy storage and release mechanism is a key feature of the design, as it allows for swift and repeatable transformations with minimal energy loss.
From Two Shapes to Many
While a bistable structure is impressive, the research team did not stop at just two shapes. They discovered that by introducing additional manipulations, they could unlock a multitude of other stable forms. By applying a twist to the lantern structure, either on its own or in combination with compression, they were able to create a variety of new, stable three-dimensional shapes. Furthermore, they found that folding the solid strips at the top and bottom of the lantern, either inward or outward, also resulted in additional stable configurations. The combination of these simple actions—compressing, twisting, and folding—allowed the researchers to coax the single piece of polymer into more than a dozen distinct shapes.
Each of these new shapes is also multistable, meaning it can exist in several different stable forms depending on the forces applied to it. For example, one variation of the structure was found to have four stable states, each accessible by a different combination of compressing and twisting. This ability to access a wide range of shapes from a single, simple design greatly expands the potential applications of the technology. A device made from this material could be programmed to transition through a sequence of shapes to perform a complex task, or it could be reconfigured on the fly to adapt to changing conditions. The researchers have also developed a mathematical model that can predict how the geometry of the initial cuts will affect the final shapes and the amount of energy stored in the structure, allowing for the custom design of lanterns with specific transformative properties.
Remote Control and Future Applications
A significant advancement in this research is the ability to control the shape-shifting process remotely. To achieve this, the researchers applied a thin magnetic film to the bottom strip of the polymer structure. By using an external magnetic field, they could then manipulate the lantern without any physical contact, inducing the same compression and twisting motions that were initially applied by hand. This capability for remote actuation is a critical step in translating this technology from the laboratory to real-world applications. It opens the door to using these structures in environments that are inaccessible or hazardous for humans, such as inside the human body or in deep-sea exploration.
The potential applications for this technology are vast and varied. The research team has already demonstrated several proof-of-concept devices to illustrate the utility of their design. These include a non-invasive gripper capable of capturing a fish, a filter that can modulate the flow of water, and a device that can rapidly expand to open a collapsed tube. In the field of robotics, these structures could be used to create soft robots that can change their shape to navigate complex environments or perform delicate tasks. In biomedical engineering, they could be used to create implantable devices that can be deployed in a compressed form and then expanded to their full size once in place. The aerospace industry could also benefit from this technology, using it to create deployable structures like antennas or solar arrays that can be packed into a small volume for launch and then expanded in space.
A New Era for Metamaterials
This Chinese lantern-inspired structure is part of a broader class of materials known as metamaterials. These are materials that are engineered to have properties not found in naturally occurring materials. In this case, the researchers have created a material with programmable shape-shifting capabilities. The work, led by senior author Jie Yin, a professor of mechanical and aerospace engineering at North Carolina State University, and first author Yaoye Hong, a post-doctoral researcher at the University of Pennsylvania, represents a significant step forward in the field of active materials.
By combining elegant design with a deep understanding of mechanical principles, the team has created a platform technology that is both versatile and scalable. The simple fabrication process, which involves cutting a sheet of polymer, suggests that these structures could be produced at a low cost and in a wide range of sizes. The development of a predictive mathematical model further enhances the potential for customization, allowing engineers to design structures with specific shapes and energy storage capacities tailored to a particular application. As research in this area continues, we may see the emergence of a new generation of smart devices and structures that can adapt to their surroundings in ways that were previously only imagined in science fiction.
