Carpenters could use the technique to make furniture or other wooden products that are shipped flat to a destination and then dried to form the desired final shape.
Doron Kam, a graduate student at the Hebrew University of Jerusalem, said despite warping being an obstacle, the research team behind the technique sought to understand this phenomenon and “harness it into a desirable morphing”.
Unlike some natural objects, artificial structures can’t typically shape themselves, said Eran Sharon, one of the project’s principal investigators. In recent years, scientists have printed flat sheets that could form themselves into 3D shapes after a stimulus, such as a change in temperature, pH or moisture content.
However, Sharon noted that such self-morphing sheets were made from synthetic materials, such as gels and elastomers. “We wanted to go back to the origin of this concept, to nature, and do it with wood,” he explained.
The team had previously developed an environmentally friendly water-based ink composed of wood-waste microparticles known as “wood flour” mixed with cellulose nanocrystals and xyloglucan, which are natural binders extracted from plants. The researchers then began using the ink in a 3D printer.
They recently discovered that the way the ink is laid down, or the “pathway,” dictates the morphing behavior as the moisture content evaporates from the printed piece.
For instance, a flat disk printed as a series of concentric circles dries and shrinks to form a saddle-like structure reminiscent of a Pringles crisp, while a disk printed as a series of rays emanating from a central point turns into a dome or cone-like structure.
The scientists learned how to program the print speed and pathway to achieve a variety of final shapes. They found that stacking two rectangular layers that are printed in different orientations yields a helix after drying.
In their latest work, the team found they can program the printing pathway, speed and stacking to control the specific direction of shape change, such as whether rectangles twist into a helix that spirals clockwise or counterclockwise.
The team said that further refinement of the technique will allow them to combine the saddles, domes, helices and other design motifs to produce objects with complicated final shapes, such as a chair.
Kam said the technique could ultimately make it possible to make wood products that are shipped flat to the end user, which could reduce shipping volume and costs: “Then, at the destination, the object could warp into the structure you want”.
Sharon added that, eventually, it may be feasible to license the technology for home use so consumers could design and print their own wooden objects with a regular 3D printer.
The team is also exploring whether they could make the morphing process reversible. “We hope to show that under some conditions we can make these elements responsive – to humidity, for example – when we want to change the shape of an object again,” Sharon concluded.
Source: E&T
