They’ve designed a new kind of soft robotic gripper that changes shape mid-task. It starts as an open loop to wrap around objects, then closes into a secure loop to lift and hold them. The technique, called loop closure grasping, lets the gripper safely lift everything from fragile produce to a full-grown adult.
This work, published in Science Advances by a team from MIT, Stanford, and the University of Florida, tackles one of the long-standing challenges in robotics in terms of how to build a single gripper that’s both adaptable and reliable, strong but gentle. Instead of forcing one design to do everything, the researchers took a different approach - let the gripper change shape to suit the task.
Why This Matters
Most robotic grippers fall into one of two camps. You have rigid tools like claw or pincer grippers, which can hold heavy items securely but struggle with delicate or oddly-shaped objects. Then there are soft, flexible grippers, which are better at adapting to shapes but aren’t great at applying force.
This new system bridges that gap by splitting the job into two parts. First, the gripper reaches out in an open-loop shape that’s easy to move and position. Then, once it’s in place around an object, it connects its free end back to its base, closing the loop and creating a stable, load-bearing structure.
It’s a simple idea with big implications: one shape for flexibility, another for strength.
How it Works
To build this two-stage gripper, the team used inflatable “vine robots” (long, soft tubes that can extend by inflating and steer through tight spaces). Think of a robotic version of those air-filled tube dancers, but with a lot more control.
Two versions were built:
- A large-scale prototype made from heat-sealed nylon, strong enough to lift a person.
- A smaller version using lightweight plastic materials for more compact tasks.
Each version has a motorized winch at the base to help retract the robot and control its motion. But the key part is the tip-fastening mechanism. Once the vine robot has wrapped around its target, it uses a clamp or latch to attach the tip back to the base, turning the open loop into a closed, tension-bearing one. That’s where the strength comes from.
This setup means the robot doesn’t have to be stiff or bulky to support weight; it relies on tension, like a hammock or a sling, which makes it strong and soft at the same time.
Experimental Validation
The researchers put the system through a variety of tests to see how it performed in both stages.
First, they looked at versatility. The open-loop gripper was able to:
- Wrap around a ball using multiple vines to form a soft, cage-like grip.
- Interlock with objects in complex ways, like forming a loop with a ring and a bucket handle.
- Retrieve a kettlebell from a cluttered bin, navigating through a space that was narrower than the gripper itself.
All of this showed how well the gripper could move and shape itself before even starting to lift.
Then came the strength and gentleness tests. The gripper:
- Lifted a 74 kg adult off a bed, proving it could support human-scale weight.
- Applied only 16.95 kPa of contact pressure during the lift, which is significantly lower than typical medical slings, which often reach 26.7 kPa.
- Safely picked up delicate items like a watermelon and a glass vase without causing damage.
These results confirmed that the closed-loop phase delivers strong support while remaining gentle, exactly what’s needed for handling fragile or sensitive objects.
What’s Next
This type of gripper could open up new possibilities in areas such as healthcare, agriculture, or disaster response, where robots need to handle heavy yet delicate items or work in tight, unpredictable environments.
What’s especially promising is that the system works well at different scales and doesn’t require bulky materials or complex joints. It’s just soft, inflatable tubing, smart sequencing, and a shape change at the right moment.
There’s still room to improve things like control and fine-tuning how the robot makes contact, but the core idea is simple, practical, and already showing real-world potential.
Journal Reference
Barhydt et al. (2025). Loop closure grasping: Topological transformations enable strong, gentle, and versatile grasps. Science Advances, 11(50). DOI:10.1126/sciadv.ady9581. https://www.science.org/doi/10.1126/sciadv.ady9581
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