4-D technology allows complex self-folding objects

Researchers have demonstrated a four-dimensional printing technology that allows creation of complex self-folding structures.
The technology, developed by researchers at the Georgia Institute of Technology and the Singapore University of Technology and Design (SUTD), could be used to create 3-D structures that sequentially fold themselves from components that had been flat or rolled into a tube for shipment.
The components could respond to stimuli such as temperature, moisture or light in a way that is precisely timed to create space structures, deployable medical devices, robots, toys and range of other structures.
The researchers used smart shape memory polymers (SMPs) with the ability to remember one shape and change to another programmed shape when uniform heat is applied.

The ability to create objects that change shape in a controlled sequence over time is enabled by printing multiple materials with different dynamic mechanical properties in prescribed patterns throughout the 3-D object.
When these components are then heated, each SMP responds at a different rate to change its shape, depending on its own internal clock. By carefully timing these changes, 3-D objects can be programmed to self-assemble.

The research creates self-folding structures from 3-D printed patterns containing varying amounts of different smart shape-memory polymers. The patterning, done with a 3-D printer, allows the resulting flat components to have varying temporal response to the same stimuli.

"Previous efforts to create sequential shape changing components involved placing multiple heaters at specific regions in a component and then controlling the on-and-off time of individual heaters," said Jerry Qi, a professor in the George W Woodruff School of Mechanical Engineering at Georgia Tech.
"This earlier approach essentially requires controlling the heat applied throughout the component in both space and time and is complicated.
"We turned this approach around and used a spatially uniform temperature which is easier to apply and then exploited the ability of different materials to internally control their rate of shape change through their molecular design," Qi said.

The team demonstrated the approach with a series of examples including a mechanism that can be switched from a flat strip into a locked configuration as one end controllably bends and threads itself through a keyhole.
The research team envisions a broad range of applications for their technology. For example, an unmanned air vehicle might change shape from one designed for a cruise mission to one designed for a dive.
Also possible would be 3-D components designed to fold flat or be rolled up into tubes so they could be easily transported, and then later deformed into their intended 3D configuration for use.

The research was published in the journal Scientific Reports.