A tiny flexible wrist can bend around corners—and grip while it does. Meet a new possibility for the tools of microsurgery.

Engineering at the millimeter scale

A tiny flexible wrist can bend around corners—and grip while it does. Meet a new possibility for the tools of microsurgery.

A little pull. A whole new angle.

Instead of a rigid hinge, this wrist bends along its length. Explore a simplified model: choose a bend, steer around the shaft, then close the jaws.

Make your move

This is a pose illustration, not a simulation of tendon forces or displacement. The paper does not yet provide that control model. The circle animation illustrates steering at a fixed bend.

1 A flexible skeleton

The 3.75 mm wrist is a stack of hollow diamond-shaped cells that deform elastically. Two-photon polymerization prints the wrist and gripper in IP-Q photoresin, with features at the micron scale.

2 Three lines to steer

Three tungsten tendons run around the wrist. Coordinated pulls bend it in different directions. Each tendon is just 25 micrometers across.

3 One line to hold

A fourth tendon runs down the center to close the gripper. In the demonstration, the bent wrist held microfiber paper, used as a tissue proxy.

Beyond a right angle.

The researchers measured more than 90° of bending in all four tested directions, with tight bend radii of 2.1–2.3 mm.

*A different setup for measurement: these tests used a wrist without the gripper and four bending tendons arranged in opposing pairs. The integrated gripper demonstration uses three bending tendons and a separate gripping tendon.

A wrist with a little memory.

Pull a tendon, then ease it back. The wrist may take a different path on the way home. Friction in the tendon channels causes this effect, called hysteresis.

At the same tendon displacement, the bend can differ depending on whether the tendon is being pulled or released. Switch the direction to see why precise control needs more than a simple pull-to-angle rule.

Pulling: the wrist follows the lower branch. At this pull position, the bend is smaller.

Qualitative illustration of hysteresis; curves are schematic, not measured data.

Built small. Still a big next step.

This is an early fabrication and motion demonstration. The researchers envision integration with a teleoperated robot for microsurgery, particularly procedures inside the eye.

Force measurements, statistical testing, a tendon-to-angle control model, and further miniaturization remain future work. The study does not establish clinical safety or performance in surgery.

A new way to reach is the beginning. Reliable, precise control is what comes next.

Based on “Toward a Millimeter-Scale Tendon-Driven Continuum Wrist with Integrated Gripper for Microsurgical Applications.” Alexandra Leavitt, Ryan Lam, Nichols Crawford Taylor, Daniel S. Drew & Alan Kuntz · University of Utah · 2023. Conceptual artwork generated with AI; experimental figure reproduced from the paper.