Researchers have found a way to bypass a major design step in 3D printing, to quickly and efficiently model and print thousands of hair-like structures – something that had previously not been possible using 3D printers.
The hope is that being able to quickly and easily print thousands of hairs will open up new designs for sensors and actuators. Jifei Ou, a graduate student in media arts and sciences and lead author on the research paper, said the work is inspired by hair-like structures in nature, which provide benefits such as warmth, in the case of human hair, and movement, in the case of cilia, which help remove dust from the lungs.
Instead of using conventional computer-aided design (CAD) software to draw thousands of individual hairs on a computer – a step that would take hours to compute – the team at MIT’s Media Lab built a new software platform, called "Cilllia," that lets users define the angle, thickness, density, and height of thousands of hairs, in just a few minutes.
The researchers began by modelling 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.
To scale up to thousands of hairs on a flat surface, Ou and his team used Photoshop to generate a colour mapping technique. They used three colours – red, green, and blue – to represent three hair parameters – height, width, and angle. For example, to make a circular patch of hair with taller strands around the rim, they drew a red circle and changed the colour 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 colour map into a model of a hair array, which they then fed to a 3D printer.
To print hairs on a curved surface 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 then developed an algorithm to locate the centre 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 rabbit's curved surface.
The researchers then used their colour mapping techniques to quickly customise the rabbit hair's thickness and stiffness.
Using these techniques, the team printed pads of Velcro-like bristles, and paintbrushes with varying textures and densities.
The researchers are now looking into how 3D-printed hair could perform useful tasks such as sensing, adhesion, and actuation.
To demonstrate adhesion, the team printed arrays that act as Velcro-like bristle pads. Depending on the angle of the bristles, the pads can stick to each other with varying forces. For sensing, the researchers printed a small furry rabbit figure, equipped with LED lights that light up when a person strokes the rabbit in certain directions.
To see whether 3D-printed hair can help actuate, or move objects, the team fabricated a weight-sorting table made from panels of printed hair with specified angles and heights. As a small vibration source shook the panels, the hairs were able to move coins across the table, sorting them based on the coins' weight and the vibration frequency.
Among other applications, Ou said 3D-printed hair may be used in interactive toys. To demonstrate, his team inserted an LED light into the fuzzy printed rabbit, along with a small microphone that senses vibrations. With this setup, the bunny turns green when it is petted in the correct way, and red when it is not.