Today, it may look as if 3D printers can produce anything, from a complete sports car, to eatable food, to human skin. However, a number of things have challenged the technology, including fur, hair and other solid range of very fine features that need a large amount of computational power and time to design and print objects.
Researchers from MIT’s Media Lab have discovered a way to avoid a key design step involved in 3D printing, to rapidly and professionally design and print thousands of structures similar to hair. The research team developed a new software platform, named “Cilllia,” in place of conventional computer-aided design (CAD) software to draft thousands of separate hairs on a computer, a process that would take nearly hours to work out. The new software allows users to describe the height, thickness, density and angle of hairs within a fraction of few minutes.
The scientists have used the new software to design a range of hair-like structures with a 50 µm resolution - nearly the thickness of a human hair. They also used a standard 3D printer to print various arrays ranging from coarse bristles to high-quality fur, onto flat and curved surfaces in different dimensions. A paper describing the study results presented at the Association for Computing Machinery’s CHI Conference on Human Factors in Computing Systems in May.
Could this technology be utilized to print hair and wigs extensions? Probably, say the investigators. However, that’s not their final target. Instead they are looking at how 3D-printed hair could be utilized to carry out useful tasks like actuation, sensing, and adhesion.
In order to show adhesion, the researchers printed arrays that function as Velcro-like bristle pads. These pads, relying on the angle of the bristles, can attach to each other with variable forces. For sensing, the team printed a small hairy rabbit figure with LED lights that illuminate whenever a person rubs the rabbit in particular direction. They also made a weight-sorting table from printed hair panels with certain heights and angels in order to observe how 3D-printed hair can help prompt or move objects. When a slight vibration shook the panels, the hairs moved the coins across the table and arranged them based on the frequency of the vibration and the weight of the coins.
According to Jifei Ou, a graduate student in media arts and sciences, the effort is inspired by hair-like structures present in nature, and these structures offer benefits such as warmness, in the instance of human hair, and movement, in the instance of cilia that help reduce dust from the lungs.
It’s very inspiring to see how these structures occur in nature and how they can achieve different functions. We’re just trying to think how can we fully utilize the potential of 3D printing, and create new functional materials whose properties are easily tunable and controllable.
Jifei Ou, Graduate Student, MIT
Ou is the lead author of the research paper, which also involved the contribution of graduate students Chin-Yi Cheng and Gershon Dublon; Hiroshi Ishii, the Jerome B. Wiesner Professor in media arts and sciences; Karl Willis of Addimation, Inc.; and Felix Heibeck, a former research assistant.
A software challenge
The resolution of current 3D printers is “already pretty high,” Ou says. “But we’re not using [3D printing] to the best of its capabilities.”
The researchers searched for things to print in order to test the limits of the technology and found hair as the perfect choice.
[Hair] comes with a challenge that is not on the hardware, but on the software side.
Jifei Ou, Graduate Student, MIT
In order to 3D-print hair with existing software, engineers would have to form hair in CAD, stretch strand and then supply the drawing through a slicer program that signifies each hair’s shape as a mesh of small triangles. Next, the program would produce horizontal cross segments of the triangle mesh and transform each cross segments into a bitmap or pixels, that could be printed out layer by layer.
Ou said that making a stamp-sized array of 6,000 hairs utilizing this method would take quite a few hours to process.
“If you were to load this file into a normal slicing program, it would crash the program,” he says.
The scientists decided to get rid of the CAD modeling completely in order to design hair. So, they created a new software platform to initially develop a single hair and after that an array of hairs, and finally to print arrays on both curved and flat surfaces.
The scientists developed a single hair by making an extended cone as a stack of less and less pixels from the bottom to the top. They modified the assembly of pixels in the cone in order to alter the hair’s dimensions, such as its angle, height and width.
Ou and his collaborators utilized Photoshop to produce a color mapping technique to develop a large number of hairs on a flat surface. They utilized three colors — red, green, and blue — to signify three hair parameters — angle, height and width. For instance, to create a circular piece of hair with taller strands surrounding the trim, they sketched a red circle and altered the color gradient and made darker hues of red become visible around the rim, indicating taller hairs. The researchers then created an algorithm to rapidly convert the color map into a hair array model and fed the model into a 3DD printer. They used these techniques and printed Velcro-like bristle pads and paint-brushed with varying densities and textures.
Compared to flat surfaces, printing hair on curved surfaces was trickier. In order to do this, the researchers first brought in a CAD drawing of a curved surface, for example, a small rabbit, and then supplied the model through a slicing program to produce a triangle mesh of the rabbit figure. They then created an algorithm to trace the center of each base of the triangle and drew a line out, vertical to the base of the triangle, to signify a single hair. Repeating this process for each triangle in the mesh formed a thick array of hairs moving vertical to the curved surface of the rabbit. The investigators then utilized their color mapping techniques to rapidly modify the stiffness and thickness of the rabbit hair.
With our method, everything becomes smooth and fast. 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?
Jifei Ou, Graduate Student, MIT
Ou says 3D-printed hair, may be utilized in interactive toys and other applications. In order to prove this, his team placed an LED light into the furry printed rabbit, together with a tiny microphone to sense vibrations. In this setup, when the bunny is petted in the right way, it turns green and red when it is not.
“The ability to fabricate customized hair-like structures not only expands the library of 3D-printable shapes, but also enables us to design alternative actuators and sensors,” the authors conclude in their paper. “3D-printed hair can be used for designing everyday interactive objects.”
Kelly Schaefer, a designer at IDEO, a design consulting firm, says “this type of work expands the possibilities of 3D printing as an industry because of the new applications it suggests.”
“Perhaps more inspiring than any single output from this team is the idea of rethinking the 3D printing process itself and the purpose of 3D printed objects,” says Schaefer, who was not involved in the research. “The Cilllia team has challenged some of the current constraints of 3D printing processes, which makes me wonder what other constraints can be challenged and potentially eliminated.”