MIT researchers program and 3D print hair-like structures

Additive manufacturing is constantly being used to print just about anything you could possibly think about. However, researchers are now pushing the limits by 3D printing extremely fine features, like those found in hair, fur and other dense arrays. These types of products require a huge amount of computational time and power to design and print.

3D printed micro-pillar structures for surface texture, actuation and sensing. Courtesy of Tangible Media Group/MIT Media Lab.

The researchers at MIT’s Media Lab have found a way to bypass this major step. By removing the design step in 3D printing, the researchers are able to quickly and efficiently model and print thousands of hair-like structures.

Traditionally, the team would have been required to uses CAD software to draw thousands of individual hairs. This task could have taken hours to compute. However, the researchers have developed a new software platform, Cilllia. This platform allows users to define the angle, thickness, density and height of thousands of hairs in a matter of minutes. The hair-like structures are designed with a resolutions of 50 microns.

The team designed and 3D printed many arrays ranging coarse bristles to fine fur on both flat and curved surfaces. The goal is to understand how 3D printed hair performs useful tasks such as sensing, adhesion and actuation.

“It’s very inspiring to see how these structures occur in nature and how they can achieve different functions,” says Jifei Ou, a graduate student in media arts and sciences and lead author of the paper. “We’re just trying to think how can we fully utilize the potential of 3-D printing, and create new functional materials whose properties are easily tunable and controllable.”

Ou points out that the resolution of today’s 3D printers are already pretty high, but for the most part, we are not using additive manufacturing to the best of its capabilities. When it came to 3D printing hair, the challenge was not a hardware one, but rather a software issue. This is partially why the team decided to do away with traditional CAD modelling.

The researchers modeled a single hair by representing an elongated cone as a stack of fewer and fewer pixels, from the base to the top. To change the hair’s dimensions, such as its height, angle, and width, they simply changed the arrangement of pixels in the cone.

Ou and the team then used Photoshop to generate a color mapping technique in order to scale up to thousands of hairs on a flat surface. Red, green and blue were used to represent the hair parameters of height, width and angle.

For example, to make a circular patch of hair with taller strands around the rim, the team drew a red circle and changed the color gradient in such a way that darker hues of red appeared around the circle’s rim, denoting taller hairs. They then developed an algorithm to quickly translate the color map into a model of a hair array, which they then fed to a 3D printer.

3D printing on a curved surface was a much greater challenge for the researchers. The team first imported a CAD drawing of a curved surface, such as a small rabbit, then fed the model through a slicing program to generate a triangle mesh of the rabbit shape.

They developed an algorithm to locate the center of each triangle’s base, then virtually drew a line out, perpendicular to the triangle’s base, to represent a single hair. Doing this for every triangle in the mesh created a dense array of hairs running perpendicular to the curved surface. The researchers then used their color mapping techniques to quickly customize the rabbit hair’s thickness and stiffness.

“With our method, everything becomes smooth and fast,” Ou explains. “Previously it was virtually impossible, because who’s going to take a whole day to render a whole furry rabbit, and then take another day to make it printable?”

Ou believes that this development can be used to many different applications and that it will enable users to design alternative actuators and sensors as well as everyday interactive objects.

www.media.mit.edu