Video: Two Different Shape-Shifting Polymers Change Shape In Water

Two different shape-shifting polymers have been announced from two different universities: Wyss Institute at Harvard University and Zhejiang University in eastern China. Both of them change their shapes when immersed in water. The one from Wyss Institute was made with 3D-printing techniques, which the team calls 4D printing since it combines 3D printing with shape-shifting materials.

As we've often reported, shape-changing materials have been under development for several years, more recently made by, or combined with, 3D-printing techniques. One advantage of using 3D printing is the ability to fine-tune material composition at each layer, such as the University of Colorado Boulder's method of making composites containing shape-memory polymer fibers. This is often seen as a mechanism for creating objects that self-assemble under the right stimuli, such as temperature or immersion in water.

(Source: New China TV/Zhejiang University)

As you can see in this video, the Zhejiang University's origami-like paper crane that forms from a plastic flake responds to the water -- but also to the water's temperature, in this case 60C. The researchers say that this material can change between different preset shapes under specific conditions. Potential applications include flexible medical equipment that changes shape in response to changes in body temperature. The team published its work in an open access article in Science Advances.

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A team at the Wyss Institute for Biologically Inspired Engineering at Harvard University and the Harvard John A. Paulson School of Engineering and Applied Sciences developed a microscale-level 3D-printing technology that prints hydrogel composites, which change when exposed to environmental stimuli like humidity and/or heat. The hydrogel composites, which contain cellulose fibrils derived from wood similar to the microstructures enabling shape changes in plants, are programmed to contain precise, localized swelling behaviors. 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.

(Source: Wyss Institute at Harvard University)

When immersed in water, the hydrogel-cellulose fibril ink undergoes differential swelling behavior both along the printing path, and orthogonal to it, as shown in this video. The team, led by Jennifer Lewis, developed a proprietary mathematical model that predicts how a 4D-printed object must be fabricated to achieve prescribed transformable shapes. Although these complex geometries are achieved with one composite ink printed in a single step, the team says it uses different materials to tune for specific properties like biocompatibility or conductivity. Smart textiles, soft electronics, biomedical devices, and tissue engineering are some of the potential applications. The work is decribed in an article in Nature Materials.

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Ann R. Thryft is senior technical editor, materials & assembly, for Design News. She's been writing about manufacturing- and electronics-related technologies for 28 years, covering manufacturing materials & processes, alternative energy, and robotics. In the past, she's also written about machine vision and all kinds of communications.