MIT‘s Computer Science and Artificial Intelligence Laboratory (CSAIL) has created a new way to 3D print objects that can move. Called Xstrings, this method prints cables inside the object so it can bend, twist, or flex right out of the printer. Normally, making something like a robotic hand or a moving sculpture takes a lot of time because the cables must be added by hand. But Xstrings does everything in one step, without any extra assembly required.
By embedding cables directly into objects during printing, Xstrings can create dynamic mechanisms. This means researchers can make things like robotic fingers that curl, sculptures that shift shape, or clothes with adjustable parts, all in one step.
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Printing Motion
Traditional cable-driven systems are common in robotics and mechanical designs, but putting them together by hand takes time and effort. Xstrings solves this by automating the entire fabrication process. Users can design their creations using specialized software, and a 3D printer then creates the full piece—cables included—so it’s ready to use right away.
MIT CSAIL postdoctoral researcher and lead author Jiaji Li says that Xstrings can save engineers time and energy, reducing 40 percent of total production time compared to doing things manually.
“Our innovative method can help anyone design and fabricate cable-driven products with a desktop bi-material 3D printer,” says Li.
The team behind Xstrings put their system to the test, printing various functional objects, including a red lizard-like walking robot, a peacock-inspired wall sculpture that opens and closes, and a robotic claw that forms a fist to grab objects. Each design shows the flexibility of Xstrings and its potential to change how engineers think about 3D printing objects that can move.
Built to Move
Xstrings lets users fully customize their designs by defining an object’s shape, size, and movement. The software provides a range of motion options, known as “primitives,” including bending (like a finger curling); coiling (like a spring tightening); twisting (like a screw turning), and compressing (like an accordion folding in).
By combining multiple motion primitives, users can create complex and lifelike movements. For example, a toy snake could incorporate a series of twists along its body, while a robotic claw could use parallel cable placement to allow each finger to move independently.
The system also gives designers precise control over where cables are secured within an object, including the anchor points (where the cable is fixed), threaded areas (the pathways the cable follows through the object), and exposed pull points (where the user applies force to activate movement).
This level of control means that, instead of just printing inert objects, Xstrings allows users to bring their designs to life in ways that were previously complicated or impractical.
Next Level
To turn these digital designs into reality, Xstrings sends the blueprint to a fused deposition modeling (FDM) 3D printer, which builds the object layer by layer. The researchers explain that during printing, the machine strategically places cables and joints within the structure, ensuring they function correctly once the object is complete.
One of the biggest challenges the researchers faced was ensuring the cables could withstand repeated use. To test durability, they subjected their printed strings to over 60,000 cycles of movement. They also fine-tuned printing conditions, settling on an optimal temperature of 260°C and a speed of 10-20 millimeters per second to ensure strong, functional designs. The result is a new kind of 3D printed object that looks and moves naturally.
How Xstrings is 3D printed. Image courtesy of MIT CSAIL.
Xstrings is already proving its potential in robotics, art, and fashion, but its possibilities don’t stop there. Li imagines a future where cable-driven 3D printing could play a role in extreme environments like outer space.
“One day, this technology could enable the rapid, one-step creation of cable-driven robots in outer space, even within highly confined environments such as space stations or extraterrestrial bases,” says Li.
The team is also exploring new ways to expand the technology’s capabilities, such as using more durable cables and experimenting with different orientations—moving beyond horizontal placement to angled and even vertical string integration. Another possibility includes developing objects that are soft on the outside but rigid inside, mimicking the structure of human skin and bones.
With Xstrings, MIT CSAIL is literally pulling 3D printing in a whole new direction. By building movement into the printing process, the team has made it possible for 3D printed objects not just to exist but also to move and interact. Whether robots assemble themselves, kinetic sculptures that move on command, or adaptive clothing that adjusts to the wearer, the applications are limitless.
In April, researchers will present the paper detailing Xstrings at the 2025 Conference on Human Factors in Computing Systems (CHI2025).
