3D-Printed “Hair” Is Useful as Sensors, Actuators and More
Michael Molitch-Hou posted on June 21, 2016 |
A group of researchers has learned to 3D print hair-like structures for a wide variety of applicatio...

3D-printed “hair” is not quite new. In 2015, researchers at Carnegie Mellon University demonstrated a method for using extrusion-based 3D printing to create plastic hair follicles from polylactic acid (PLA). The applications of the technology as showcased in the study, however, were not much more useful than giving printed ponies and troll dolls brand new dos.

MIT researchers have learned to 3D print “hair” with DLP 3D printers. (Image courtesy of MIT Media Lab.)
MIT researchers have learned to 3D print “hair” with DLP 3D printers. (Image courtesy of MIT Media Lab.)

A team from MIT has since broadened the capabilities of 3D printing hair, while also developing new software for controlling the properties of the printed hair follicles for specific applications. In a recent study, researchers from MIT Media Lab describe methods for printing hairs of varying thicknesses onto flat and curved surfaces for use as sensors, actuators, Velcro and more.

In the case of Carnegie Mellon, the team created plastic hair by extruding a small dot and pulling the print head away while the material cooled. The MIT researchers, in contrast, were able to write a piece of software for 3D printing hairs in a much more controllable way using digital light processing (DLP) 3D printing technology.

The ability to print features as fine as hair with SLA was not the biggest hurdle for the MIT group. 3D printing with an Autodesk Ember 3D printer provided the team, led by Jifei Ou, with the print resolution to create 50 micron follicles on their prints. Instead, the most significant obstacle was the amount of data represented by thousands of tiny hairs—something that proved difficult for either CAD or slicing software to handle.

CAD software doesn’t actually create three-dimensional representations for hair models, but rather paints the illusion of hair using 2D images. Even if one were to create 3D models of every strain of hair, the Slicer software, which converts a 3D model into instructions that a printer uses for fabricating an object, would not be able to process that amount of data and would likely crash. For this reason, the MIT group opted for a bottom-up approach.

With Cillia, users can control the length, density, thickness and angle of 3D-printed hair. (Image courtesy of MIT Media Lab.)
With Cillia, users can control the length, density, thickness and angle of 3D-printed hair. (Image courtesy of MIT Media Lab.)

Rather than model hair in a CAD program, the researchers conceived of their hair follicles as individual pixels assembled into the shape of a cone. The features of a strand of hair were then represented as RGB values with graphic bitmaps in Photoshop, so that the R-value represented the angle of the hair on the X-axis, the G-value stood for the angle of Y-axis and the B-value symbolized the height of the hair.

The team then built an accompanying program called Cillia for manipulating the angle, thickness, density and height of the hairs that would be applied to a 3D model. Adjusting simple sliders, users can create anything from thick patches of long fur to sparse, short bristles. These swatches can then be applied to standard STLs imported into Cillia, though hair jutting out at angles more extreme than 60 degrees will not be printable. This is then exported as a presliced file for 3D printing.

Custom brushes can be 3D printed with the MIT team’s process. (Image courtesy of MIT Media Lab.)
Custom brushes can be 3D printed with the MIT team’s process. (Image courtesy of MIT Media Lab.)

The applications explored by the Media Lab team are fascinating. Of course, there were the straightforward aesthetic uses for hair-like features on 3D prints, such as printing a furry model of a rabbit and a spiny model of a hedgehog. This application was given a more utilitarian purpose with the 3D printing of custom paintbrushes with varying bristle qualities.

More interesting perhaps was the use of 3D-printed hair as Velcro. The team was able to print swatches of hair and stick them together, providing inspiration for 3D printing designs with built-in adhesive properties.

Based on the angle of the hairs, vibrations will push an object along a specific path. (Image courtesy of MIT Media Lab.)
Based on the angle of the hairs, vibrations will push an object along a specific path. (Image courtesy of MIT Media Lab.)

Inspired by the cilia found in nature, the Media Lab group has demonstrated a number of instances in which 3D-printed hair could act as passive actuators. By altering the angle at which the follicles are pointing, the researchers could guide the motion of an object in contact with those follicles.

The angles of the hair will also cause an object to rotate in response to vibrations. (Image courtesy of MIT Media Lab.)
The angles of the hair will also cause an object to rotate in response to vibrations. (Image courtesy of MIT Media Lab.)

Vibrating blocks with hairy surfaces resulted in a conveyor belt system that would pass objects along in a predetermined pattern. 3D printing hairs into the interior of a ring allowed for passive rotary properties so that, when vibration was applied, a rod would be forced to spin in a specific direction, as showcased in the video below.

Attaching a microphone to a patch of hair, the researchers determined, could make for a tactile sensor. When the bristles are touched, the microphone can pick up the sound, which can be translated into data for a number of uses. For instance, this method could be implemented to determine the speed at which an object traveled over the hair or as an on-off switch for lighting up an LED.

Vibrations from a smartphone can cause a windmill to spin along an axis determined by the angle of 3D-printed hairs. (Image courtesy of MIT Media Lab.)
Vibrations from a smartphone can cause a windmill to spin along an axis determined by the angle of 3D-printed hairs. (Image courtesy of MIT Media Lab.)

Just as Lawrence Livermore National Laboratory looks into creating new types of foam with 3D-printed microstructures, research further demonstrates how changing the geometry of an object at a microscopic level can affect its larger physical properties. The results of such research will likely change the way everyday objects are designed altogether and, in turn, create a future that may be unpredictable from the perspective of today.

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