Last year, we carried an item on 4D printing, which created quite a stir – although we did try to make it clear that it was unlikely to be an overnight sensation, and a lot of work is still needed to convert this extraordinary concept into a commercial process on an industrial scale. Nevertheless, by popular demand, here is a recap on some developments within the last months.
The 4D printing technique first invented at MIT in 2013 consists of smart materials that adapt and re-program their properties, functionality or shape on demand, based upon external stimuli (such as submersion in water, or exposure to heat, pressure, current, ultraviolet light, or some other source of energy). Researchers are combining different types of plastics and fibres to create smart materials that self-assemble or change shape after 3D printing. Here, the fourth dimension relates to the time taken for the self-transformation. With the addition of time (a stimulus) to additive manufacturing, objects can become adaptable: self-evolving structures, as some researchers call them.
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4D printing takes 3D printing to an entirely new level; an exciting emerging technology for creating dynamic devices that can change their shape and/or function on-demand and over time. The technique combines smart actuating and sensing materials with additive manufacturing techniques to offer an innovative, versatile, and convenient method for crafting custom-designed sensors, robotics and self-assembling structures.
A team from Harvard’s Wyss Institute at the esteemed Ivy League school, under the management of Jennifer Lewis, have developed a gel-like composite ink containing miniature fibers of cellulose, an organic compound found in plants is being used to mimic a plant’s ability to alter its shape and formation based on environmental stimuli. Specifically, the group intends to develop a printable substance capable of mimicking the way plants respond and react to precipitation or sunlight. The resulting cellulose-heavy composite allowed them to accomplish this very goal.
By aligning cellulose fibrils during printing, the hydrogel composite ink is encoded with anisotropic swelling and stiffness, which can be patterned to produce intricate shape changes. The anisotropic nature of the cellulose fibrils gives rise to varied directional properties that can be predicted and controlled. Just like wood, which splits more easily along the grain than across it, when it is immersed in water the hydrogel-cellulose fibril ink undergoes differential swelling along and orthogonal to the printing path. Combined with a proprietary mathematical model developed by the team that determines how a 4D object must be printed to achieve prescribed transformable shapes, the new method opens up new potential applications for 4D printing technology, including smart textiles, soft electronics, biomedical devices, and tissue engineering.
One potential application is the possibility of printing new “skin” for skin grafts, capable of freely changing shape over time, not to mention medical implants. “We can now generate structures that will change shape and functionality without external intervention,” said MIT mathematician Dan Raviv. “We want to print parts that can survive a lifetime inside the body if necessary.”
4D printed smart cities
Imagine a 4D-printed water pipe that could adapt to ground changes by expanding or contracting – or even mimicking the way the human intestine works by pulsating to drive water through itself. 4D printing could lead to the development of smart objects that can react to changing environmental conditions.
As MIT’s Self Assembly Lab points out, 4D printing can imbue objects with “robotics-like behavior without the reliance on complex electro-mechanical devices.”
Other possible uses for 4D printing might even include entire buildings, capable of arriving in flat-pack form, only to assemble themselves when heat, gravity, water or any other one of a number of possible stimuli are added. And how about a road that can heal its own potholes? Scientists and engineers are only just beginning to think about the possibilities.
Self-folding structures
Researchers from the Singapore University of Technology and Design and the Georgia Institute of Technology developed a 4D printing technology that makes complex self-folding structures possible. It could be used to create three-dimensional structures that can fold themselves sequentially from components and rolled into a tube or flattened for shipment.
This could pave the way for the creation of vehicles that can shift shape when necessary. The team used shape memory polymers, or SMPs, that can remember one shape and transform to another once uniform heat is applied.
H. Jerry Qi, from the Georgia Institute of Technology, said that earlier efforts to create components that can sequentially change shape involved placing several heaters at particular regions in the component and controlling the on and off time of each of these heaters, a process that he described as complicated.
Additional resource:
The Current State of 4D Printing Technology [PODCAST]
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