Mechanical Engineering Magazine

TECH BUZZ

ENGINEERS DEVELOP A MEANS TO CONTROL THE CURVATURE OF PLASTICS USING JUST INK AND HEAT.

Researchers have designed and built small, self-folding structures for years. But the shapes that they could design have always been limited by the straight-line hinges embedded into the material. Geometric solid shapes like cubes and pyramids were easy; more complex, flowing shapes were impossible.

Now, a team of engineers at North Carolina State University in Raleigh has developed a technique using black ink to make 2-D plastic sheets curve into

3-D structures, such as spheres, tubes, bowls, and even more complex shapes.

Michael Dickey and Jan Genzer, professors of chemical and biomolecular engineering at N.C. State, published their paper in the Royal Society of Chemistry journal, Soft Matter.

“The project really started with (stu-
dents Russ Mailen and Amber Hubbard)
just trying different ink patterns in the
lab. We thought it would be interesting to
use thermoplastics since they are used
for many applications in everyday life,”
Dickey said. “We want to create materials
that are initially flat and then transform
into 3-D objects in response to some
stimuli, such as light, heat, or micro-
waves.”
To make their curved shapes, the team
used a conventional inkjet printer to print
bold, black ink lines onto a pre-strained
plastic sheet. The printed sheet was then
cut into a pattern and placed under a heat
lamp. The black lines absorbed more
energy from the light than the rest of the
material, and the plastic heated and con-
tracted at those points, creating a hinge
around which the sheet can deform.

“Consider the challenge of wrapping
a soccer ball with wrapping paper. It is
impossible to do without crumpling the
paper,” Dickey said. “The only way is with
material that can deform. We are essen-
tially using the ink to dictate where the
sheet deforms in response to light, and
create curvature.”
By varying the width of the printed
hinges, the researchers can adjust the