New 4D Printed Composite Material is Capable of Complex Movements

By using additive manufacturing technology, researchers at the University of Pittsburgh’s Swanson School of Engineering and Clemson University have developed a new hybrid material that is capable of moving independently when exposed to heat or light. What makes this 4D printed material unique is the ability to control the amount of heat and light exposure to create complex movements and transformations. The material was made by combining photo-responsive fibers with thermo-responsive gels that not only interact with each other but will independently react to either heat or light. The material is well-suited to the development of assistive devices that can adapt and display distinct behavior based on exposure to specific environments.

A research paper detailing the new material and its uses, called “Stimuli-responsive behavior of composites integrating thermo-responsive gels with photoresponsive fibers,” has been published by the journal Materials Horizons. The research was conducted by distinguished professor of Chemical and Petroleum Engineering at Pitt Anna C. Balazs and associate professor of Materials Science and Engineering at Clemson’s College of Engineering and Science Olga Kuksenok. They determined that these composite materials would exhibit highly reconfigurable behavior while also being quite mechanically strong, two important traits needed for any material intended to be used for biomimetic four-dimensional printing.

Balazs and Kuksenok created their 4D printed material by embedding a series of light-responsive fibers coated with spirobenzopyran (SP) chromophores into a temperature-sensitive gel. The new composite material will display a varying degree of behaviors and movements based on how much light and heat it is being exposed to.

“If we anchor a sample of the composite to a surface, it will bend in one direction when exposed to light, and in the other direction when exposed to heat. When the sample is detached, it shrinks like an accordion when heated and curls like a caterpillar when illuminated. This programmable behavior allows a single object to display different shapes and hence functions, depending on how it is exposed to light or heat,” says Professor Kuksenok.

So by regulating the heat and light exposure, the substance displays a wide range of movement that can be programmed by printing specific combinations and configurations of the fibers and gel. 4D printed objects have previously been made that react to a specific stimuli, either heat or light, using different materials printed in alternating concentrations. Then when the amount of stimuli is regulated or controlled it will cause specific movements. But by combining two of these reactive materials Balazs and Kuksenok have developed a method for much more complex, controllable and versatile movements. For instance the material could be incorporated into bionic limbs, used to develop surgical aids and even artificial joints that could prove essential to developing new flexible robots and adaptive devices.

“In 4D printing, time is the fourth dimension that characterizes the structure of the material; namely, these materials can change shape even after they have been printed.  The ability of a material to morph into a new shape alleviates the need to build a new part for every new application, and hence, can lead to significant cost savings. The challenge that researchers have faced is creating a material that is both strong and malleable and displays different behavior when exposed to more than one stimulus. Robots are wonderful tools, but when you need something to examine a delicate structure, such as inside the human body, you want a ‘squishy’ robot rather than the typical devices we think of with interlocking gears and sharp edges. This composite material could pave the way for soft, reconfigurable devices that display programmed functions when exposed to different environmental cues,” explained Professor Balazs.

The fact that these complex movements and behavior were created with a single composite material is the most significant portion of their research. It shows a working example of the viability of combining multiple stimuli-responsive materials to create complex and dynamic movements that are both controllable and can be reliably repeatable. The next step for Balazs and Kuksenok is to refine the composite and orientation of the light-sensitive fibers to simulate a hand-like structure capable of gripping and holding movements.  Discuss this new material in the 4D Printed Composite forum thread on 3DPB.com.