Matt Strong

Matt Strong

CS PhD at Stanford University

← Paper Digest

Helping Hand: A Continuum Robotic Grasper for Traction in Single-Channel Endoscopic Submucosal Dissection

Bendavid Maimon, Thompson Wong, Aedan Mangan, Sukjun Kim, Michael C. Yip, Tania K. Morimoto

November 2026

TL;DR The Helping Hand is a tendon-driven, notched Nitinol continuum grasper with a slot at its base for an electrosurgical knife, so tissue traction and cutting both fit through one 3.7 mm colonoscope channel. It applied about 0.33 N of traction at every tested phantom height, and with the knife it removed a tissue sample from ex vivo chicken thigh in one piece in 15 min.

What they do

In endoscopic submucosal dissection (ESD), a physician cuts a large polyp out of the colon wall in one piece. Pulling on the partly freed flap (traction) keeps the cutting plane visible. However, existing traction tools either add bulk at the endoscope tip or need a dual-channel endoscope. The Helping Hand passes an articulated grasper and an electrosurgical knife through a single 3.7 mm working channel.

How it works

  • Notched Nitinol tube (3.5 mm outer diameter) with two tendon-driven segments. The proximal segment has one knife-exit notch and four lifting notches. The distal segment has eight notches facing the other way, so the two segments form an S bend that aims a 1 mm biopsy-forceps grasper.
  • Knife slot. The knife, an insulated 1.0 mm steel rod, runs inside the tube and exits through a 2.0 mm slot at the base once the first notch bends. 3D-printed routers keep the tendons, grasper and knife apart.
  • Fabrication and actuation. Two CNC milling operations on a reusable fixture cut the notches. Four lead-screw units drive the two tendons, the knife and the grasper. Load cells measure tension in both tendons, and a micro-ROS link connects the units to ROS 2.
  • A constant-curvature model maps tendon displacements to tip pose.

Results

  • Workspace, tracked with an EM sensor: the model overestimates tip travel. The normalized RMS error (NRMSE) is 33.9% for the proximal segment and 9.10% for the distal segment, which the authors attribute to tendon stretch, actuator compliance and friction.
  • Traction on an 18 mm silicone polyp mounted on a force sensor, at 9 N proximal tendon tension, with three trials at each of four heights 4 mm apart: resultant force 0.33 ± 0.02 N and normal (lifting) force 0.27 ± 0.04 N. The grasper produced traction at every height.
  • Ex vivo, with the device on a mock endoscope tip, the grasp-retract-cut workflow removed the target region of chicken thigh en bloc in 15 min.

Limitations

The kinematic model ignores tendon elongation, compliance and friction. Tendon tension was controlled open loop, so traction was not regulated during cutting. The resection was a benchtop demonstration on chicken tissue, with the device on a mock endoscope moved by hand.

Figures

From Figure 1: The Helping Hand has two bending segments and a grasper at the tip. A slot at its base lets an electro...
From Figure 1: The Helping Hand has two bending segments and a grasper at the tip. A slot at its base lets an electrosurgical knife extend for cutting while the grasper holds the tissue.
From Figure 3: Exploded view of the Helping Hand, with the medial and proximal routers and the grasper collet.
From Figure 3: Exploded view of the Helping Hand, with the medial and proximal routers and the grasper collet.
From Figure 8: One phantom traction trial: resultant and normal force on the phantom and the two tendon tensions over...
From Figure 8: One phantom traction trial: resultant and normal force on the phantom and the two tendon tensions over time, through articulation, grasping, traction and release.
From Figure 9: En bloc resection in ex vivo chicken thigh from the tip of a mock endoscope: alignment, knife exposure...
From Figure 9: En bloc resection in ex vivo chicken thigh from the tip of a mock endoscope: alignment, knife exposure, grasping, traction and first incision, lifting the cut flap, removing the specimen, and a close-up of the resected region.
Abstract

Endoscopic submucosal dissection (ESD) is a minimally invasive approach for removing large polyps from the colon and offers many benefits compared to other surgical approaches. However, ESD is technically very challenging to perform, leading to limited adoption by physicians. We propose the Helping Hand, a two-segment continuum robotic grasper that, together with an electrosurgical knife, enables tissue traction and cutting within a single 3.7 mm working channel. We achieve this functionality by creating a slot at the base of the Helping Hand that lets the electrosurgical knife extend out, enabling countertraction and cutting through one instrument lumen. We evaluate the Helping Hand's workspace and its ability to provide traction forces from different starting configurations. Finally, we demonstrate the full workflow by isolating and removing tissue in an ex vivo chicken thigh, illustrating the potential for the Helping Hand to help improve ESD procedures.

Summaries are written automatically from each paper's text. Figures and videos come from the paper and its project page; all credit goes to the authors.