3D printing research just made a 40-year-old concept a reality

When we think of zippers, we think of a 2D structure that allows users to close two parts of a garment. Pulling a slider up and down between two rows of facing teeth allows the zipper to close and open smoothly. Applying the same concept to a three-sided fastener would result in a 3D zipper that could be used to quickly close or open structures that could benefit from such a mechanism. Such a device is called a “Y-zipper” and existed only as a concept until recently. Demonstrated and patented over 40 years ago, the original Y-zipper was not easy to manufacture. But today’s 3D printing technology has allowed researchers at MIT’s Computer Science and Artificial Intelligence Laboratory (CSAIL) to bring it back to life and turn the Y-zipper concept into a product that could one day be manufactured at scale for specific scenarios.

According to MIT News, William Freeman was an electrical engineer at Polaroid in 1985 when he entered an Innovative Design Fund competition. The prize was $10,000 for inventions related to clothing and textiles. The judges rejected Freeman’s proposal, but the engineer kept the difficult-to-make prototype and patented the invention. More than 40 years later, Freeman is a professor at MIT and other MIT engineers have developed a simpler method to make his three-sided zipper using 3D printing technology.

Jiaji Li, a researcher at MIT CSAIL and lead author of the modern version of the Y-zipper, and his team developed the software that allows 3D printers to create the 3D zipper components that can be precisely connected using a 3D cursor. The resulting three-sided zipper becomes an object whose stiffness changes as the actuator moves.

When not in use, the Y-zipper resembles a squid, according to MIT. Its three arms can be compared to tentacles. They are flexible and loose, as each side offers little rigidity on its own. But when the actuator rises to close the three-sided zipper, the teeth on all three sides fit together, creating a rigid structure. The software allows the 3D printer to create Y-zippers of different shapes, depending on their purpose.

The scientists demonstrated concepts for the Y-zipper to form a rigid vertical rod that could be used as a leg in a robot that needs to navigate complex terrain. A concept robot with four Y-zippered legs was able to reduce its height to pass under obstacles, or increase it to step over rocks on the ground. A different concept proposed a medical device intended to support a broken wrist. In this scenario, one of the three parts of the Y-zipper was 3D printed into a wrist sleeve, allowing it to remain flexible to support wrist movement during the day. At night, the user connected the other two parts of the Y-zipper using a slider, transforming the sleeve into a rigid support protecting the healing wrist.

A third concept showed a Y-zipper structure added to a tent. A user only needed 80 seconds to assemble a simple tent instead of the usual six minutes. Adding four motorized actuators to the four Y-zippers could reduce assembly time to less than 60 seconds. Finally, the researchers also showed the potential of using Y-zips for art installations that require objects to change shape or rigidity, as shown in the flower experiment in the video above.

2D zippers found on clothing are relatively durable, although they can become damaged over time and need to be replaced. For 3D printed Y-zippers, durability may be even more important. For example, the flexible Y-zipper legs of a robot that may be used in exploration or search and rescue missions must be durable enough so that the robot can reliably cover large distances. MIT researchers experimented with two types of plastics used in 3D printing: polylactic acid (PLA) and thermoplastic polyurethane (TPU). The former was better for heavier loads, while the latter was softer. They also conducted an experiment in which an actuator opened and closed continuously to test the durability of the device. After 18,000 cycles the Y-zipper broke.

These tests suggest that 3D-printed plastic Y-zippers could be suitable for specific uses, such as adding rigidity to a medical sleeve. But other uses may require more durable materials to prevent three-sided zippers from malfunctioning and losing their rigidity. MIT researchers are considering metal as a potential material for Y-zippers, although it’s unclear how a metal model would be designed. 3D printing is the key technology to manufacture the Y-zipper components, as the software ensures that the three zipper components match the geometry and fit to the millimeter and that the teeth adjust precisely as the slider moves.

The perfect match also depends on a factor that scientists could not control: the environment. The researchers envisioned use in aerospace for three-sided zippers, which could be used as tentacles to grab objects near a spacecraft. In such a scenario, debris could be a problem, as it could impact the compression and decompression processes.