Sep 22, 2015 | By Kira

Folding and unfolding structures are ubiquitous in nature (think of insect wings, or blossoming flowers, or tree leaves) and in recent years have attracted increasing interest for technical applications. Origami techniques, for example, have been studied by engineers for uses in space exploration, foldable batteries, biomedical devices and even shopping bags. Now, scientists have found a way to 3D print smart shape memory polymers (SMPs) that can self-fold into precise, predetermined shapes when exposed to uniform heat. These structures could be rolled or flattened for shipment, and then self-assemble on-demand to create deployable space structures, medical devices, solar cells, robots, airbags and other tools.

SMPs are smart digital materials with different shape memory behaviours. They can sense environmental changes, such as heat, moisture, or light, and react accordingly, going from one shape to another in a predetermined sequence. 3D printing technology enables the printing of multiple SMPs, each with different dynamic properties in prescribed patterns. This means that the entire structure can be heated evenly, but each SMP will respond at a different rate according to its precise material properties and internal clock. By carefully timing these changes, researchers can set-up complex structures without the risk of collisions between the components during the folding/unfolding processes.

(a) The schematic graph of the interlocking SMP component. (b) The ROM simulation of the sequential folding resulting in interlocking, and (c) the collision indices of the chosen design. (d) The comparison of experiments (plan and side views) and the ROM simulations (red lines)

“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,” explained Georgia Tech Professor Jerry Qi. Rather than going through the complicated approach of controlling the heat applied through the component in both space and time, they turned to 3D printing. “We have exploited the ability to 3D print smart polymers and integrate as many as ten different materials precisely into a 3D structure,” said Martin L. Dunn, a professor at SUTD.

In order to demonstrate this pioneering approach, the team showed a mechanism that can be switched from a flat strip into a locked configuration as one end threads itself through a keyhole. They also showed off a flat sheet that can fold into an interlocking box.

(a) A USPS mailbox is folded into a box by following a sequence of folding. (b) A programmed 3D printed sheet with different materials assigned at different hinges. (c–f) The design of the folding box with some details at the hinges. (g–j) Upon heating, the sheet folds into a box with self-locking mechanism.

The real-world applications for this technology range from aerospace technology to shipping infrastructure. For example, an unmanned air vehicle designed for a cruise mission could remotely self-assemble into a dive jet. Also, flat or rolled-up components could easily be stored in shipping trucks, and deploy into their 3D structures only upon arrival.

According to the researchers, with self-folding devices, expensive infrastructure investments such as robotic arms that automate the folding are not required. In addition, the SMPs can be chemically tuned to achieve biocompatibility and biodegradability, and can therefore be used in biomedical and aerospace applications. Professor Dun said that there is also the potential to expand this concept and enable the 3D printing of SMPs with dynamic mechanical properties that vary continuously in 3D space.

Yiqi Mao, a postdoctoral fellow at Georgia Tech, shows a folded box structure produced from smart shape-memory materials. The materials were created with the 3-D printer shown with him.

The research was conducted by scientists at the Georgia Institute of Technology and the Singapore University of Technology and Design (SUTD) and was reported in the journal Scientific Reports. It was funded by the U.S. Air Force Office of Scientific Research, the U.S. National Science Foundation and the Singapore National Research Foundation. In addition to Dunn and Qi, the team included co-author Yiqi Mao and three Georgia Tech collaborators: Kai Yu, Michael Isakob and Jiangtao Wu.

 

 

Posted in 3D Printing Technology

 

 

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