In 1985, Bill Freeman’s three-sided zipper was rejected and left in his garage; 40 years later, MIT revived it as a shape-shifting fastener |

In 1985, electrical engineer Bill Freeman imagined a zipper that could do more than join two pieces of material. His three-sided design used a slider to bring three strips together, potentially changing the shape and stiffness of objects. The idea was rejected by an innovation fund, but Freeman patented the mechanism and kept his prototype in his garage. Four decades later, researchers at MIT’s Computer Science and Artificial Intelligence Laboratory have revisited the concept using 3D printing and digital design tools. Their Y-zipper can transform from a flexible, open structure into rods, curves and other shapes, with potential applications ranging from tents to robots.

How Freeman’s rejected 1985 zipper became a patented prototype

Freeman’s original idea dates to 1985, when he was working as an electrical engineer at Polaroid. An advertisement in Scientific American from the Innovative Design Fund caught his attention. The fund was offering up to $10,000 for inventive prototypes involving areas such as clothing, textiles and home decor, as reported by Massachusetts Institute of Technology (MIT).Freeman submitted an idea that looked familiar at first glance but worked in a very different way. Instead of the two strips found on a conventional zipper, his version used three. He constructed the prototype with narrow wooden teeth attached to belts, arranging the strips around a triangular form. A slider could travel around the structure and draw the three sides together.Freeman imagined the mechanism acting almost like a mechanical switch, allowing objects such as chairs, tents and bags to move between softer, more flexible configurations and stiffer ones that could hold their shape. His proposal was rejected, but Freeman patented the design and kept the prototype in his garage. For decades, the three-sided zipper remained an idea waiting for the right manufacturing technology.

Four decades changed what the design could do

Earlier attempts at adjustable stiffness were not easily reversible or required manual assembly, which the CSAIL team set out to improve with an automated design tool. By the time MIT’s Computer Science and Artificial Intelligence Laboratory (CSAIL) began looking at the concept again, 3D printing offered a much more practical route. The research team developed a system that lets a person design a Y-shaped fastener digitally before producing it from plastic.The software gives users control over the dimensions and movement of the three strips. They can specify their lengths and decide the direction and angle in which the pieces should bend. Four basic movement patterns are available: straight, arched, coiled and twisted.That changes the role of the zipper. Rather than simply joining two surfaces, the printed mechanism can be incorporated into a larger object and help determine its final shape.When the Y-zipper is open, its three arms can spread apart. Once zipped, they draw together and form a more compact structure. Depending on its design, the result can resemble anything from a rod to a curved or twisted shape.

PC: MIT

How the Y-zipper could reshape camping and medical gear

Camping equipment was among the practical demonstrations explored by the MIT team. A tent supported by a Y-zipper can be designed so that its three arms connect to different parts of the canopy. According to MIT, pitching a tent alone can take up to six minutes. With the Y-zipper, it can be done in about one minute and 20 seconds.The mechanism provides a way of storing an object in a less rigid form and then giving it structure when needed. That distinction could be useful in equipment that has to be carried, packed and assembled repeatedly.The idea is not limited to camping gear. The researchers also tested the fastener around a wrist cast, where its changing stiffness could allow the support to be loosened at certain times and tightened when greater restraint was required.For wearable equipment, that ability to change shape without replacing the device could prove useful. The Y-zipper effectively becomes part of the structure rather than simply acting as a closure.

The zipper that can change a robot’s shape on demand

The MIT team also looked beyond manually operated versions. A motor can be attached to a Y-zipper after it has been fabricated, allowing the mechanism to open and close automatically. MIT describes an adaptive robotic quadruped built with the mechanism. The robot could potentially change the size of its legs, standing taller or lower as needed.The underlying idea is fairly simple. Instead of building a robot with a completely fixed geometry, some of its structure could be allowed to change when required.A similar principle was used for an experimental piece of kinetic art. The team made a long, winding flower that could open when a motor pulled the zipper into its closed position. The movement turned the fastener into an actuator for changing the shape of the artwork.

The Y-zipper was tested through 18,000 opening and closing cycles

The researchers tested two common 3D-printing plastics, polylactic acid (PLA), and thermoplastic polyurethane (TPU). The materials behaved differently under load. PLA could withstand greater forces, while TPU offered more flexibility.The team then subjected the Y-zippers to repeated opening and closing. An actuator continued cycling the mechanism until it broke, after about 18,000 cycles. Computer simulations offered an explanation for why the structure could tolerate that amount of repeated movement. Its elastic form spreads the stresses produced when the fastener is carrying a load, rather than concentrating them at one point. The researchers are already considering stronger materials, including metal, for future versions. Larger Y-zippers could also be useful, although the team’s existing 3D-printing equipment limits the scale at which they can currently be produced.