image: This system is equipped with a hydraulic-driven 3 DOF-soft cutting arm and a 3-jaw teleoperated soft grasper system for cutting and grasping lesions inside the colon, respectively. The soft manipulator (i.e., soft robotic arm) and grasper (i.e., end-effector) are operated by an electricity-free delta structure master device.
Credit: Kefan Zhu, The University of New South Wales.
Colorectal cancer is the third most common malignancy worldwide. While conventional laparoscopic resection is already minimally invasive, it still requires an abdominal-wall incision and relies on relatively rigid instruments. Endoscopic submucosal dissection (ESD) performed through natural-orifice transluminal endoscopic surgery (NOTES) can remove early lesions via natural lumens, yet most existing ESD robots are cable- or motor-driven: long actuation paths introduce friction and hysteresis, the hardware is bulky and costly, and accuracy therefore suffers inside the tortuous, narrow intestinal tract. “To overcome these limitations, we propose a fully motor-free, hydraulically actuated master-slave soft-robotic system that combines a steerable, elongating soft arm with a leech-inspired three-finger grasper.” said the author Kefan Zhu, a researcher at The University of New South Wales, “Using incompressible fluid for actuation offers low friction, high compliance and strong grasping force, aiming to improve reach, safety and fine manipulation for ESD throughout the colorectum.”
The platform adopts a completely motor-less, hydraulic master–slave architecture. On the proximal side, a Δ-structure joystick built from three syringe–Scotch-yoke amplification units provide a four-DOF end effector; through a 1.6 m pressure line it maps the operator’s subtle hand motions to the slave with a 1.45-fold torque gain, while independently driving the grasper’s opening and closing for purely mechanical teleoperation. The slave hosts two soft arms. The first, a three-chamber hydraulic soft cutting arm (SCA) about 5.5 mm in diameter and 35 mm long, uses three artificial muscles arranged 120° apart to deliver two bending DOFs and one axial extension DOF, with a 0.3 mm electrocautery knife at the tip for precise dissection. The second is a three-finger soft grasper (TSGS) just 4 mm × 8.5 mm: inspired by a leech’s anterior sucker, its Y-shaped fingers close via a helically wound hose muscle and reopen passively via a pre-stretched elastic band, enabling self-centering, evenly distributed grasping in confined spaces. Each arm offers three DOFs, allowing omnidirectional bending, extension or gripping; together they deliver up to 3.88 N of pulling force and sweep a 40 mm rotational envelope that spans the colorectal workspace. Leveraging the low friction and high compliance afforded by incompressible-fluid actuation, the system can complete the full “grasp–lift–cut–retrieve” ESD workflow in vivo, enhancing access and safety for early deep-seated intestinal lesions.
System-level evaluations show that the soft-robotic platform combines force, precision and endurance. Bench tests revealed that the soft cutting arm elongated 70 mm (100% strain) under 0.2–0.6 MPa and swept a 40 mm rotational envelope—enough to cover the entire colorectal workspace. The leech-inspired grasper generated a peak pulling force of 3.88 N at a 0.52 MPa pressure differential, comfortably exceeding the 2.26 N ESD threshold and outperforming comparable systems. In pre-programmed path-tracking trials the mean error for rectangular and circular trajectories was only 0.19–0.21 mm, confirming sub-millimetre positioning accuracy, while 11 delay measurements averaged 0.089 s—well below the 150 ms safety limit—and a 40-minute durability cycle produced just 0.9 % positional drift. In vitro silicone-colon models and ex vivo porcine-colon experiments further demonstrated the full “grasp–lift–cut–retrieve” ESD workflow: the grasper securely lifted target tissue and the 0.3 mm electrocautery knife completed dissection and closure of both simulated and real mucosal lesions. The system achieves a 100 % colorectal reach rate, ~0.2 mm trajectory error and the highest grasping force among peers within a 5.5 mm diameter, giving it clear advantages in flexibility and safety over traditional cable- or motor-driven platforms.
Although the hydraulically driven soft robot already outperforms most peer platforms in traction, reach and sub-millimetre accuracy, there are still several issues that need to be addressed. First, the viscoelastic nature of the artificial muscles causes nonlinear hysteresis in the hydraulic loop, so the unloading force is lower than the loading force, hampering fine force control. Second, the mean trajectory error (≈ 0.20 mm) meets ESD requirements but still falls short of the 0.15 mm benchmark reported for motorised RMIS systems. Third, the operator currently relies solely on visual feedback; the absence of haptic cues limits the safety margin during delicate mucosal manipulation. Validation has so far been confined to bench, in-vitro silicone and ex-vivo porcine-colon tests, leaving unresolved questions about blood contamination, hydraulic leakage and sterilisation/reuse under true physiological conditions. “To address these issues, we plan to (i) integrate a haptic-feedback channel at the master side for better perception of tissue tension and cutting depth; (ii) pair real-time image processing with motion-compensation algorithms to mitigate errors caused by respiration and peristalsis; (iii) further miniaturise the hydraulic arms and grasper while developing quick-swap end effectors (suction, suturing, etc.) to enable NOTES procedures through even narrower natural orifices and multi-instrument collaboration; and (iv) advance to in-vivo large-animal trials and design disposable or sterilisation-friendly fluid circuits to pave the way for clinical translation.” said Kefan Zhu.
Authors of the paper include Kefan Zhu, Chi Cong Nguyen, Bibhu Sharma, Phuoc Thien Phan, Trung Thien Hoang, James Davies, Adrienne Ji, Emanuele Nicotra, Jingjing Wan, Patrick Pruscino, Sumeet Walia, Tat Thang Vo-Doan, Soo Jay Phee, Shing Wong, Nigel H. Lovell, and Thanh Nho Do.
The authors acknowledge support from the UNSW Scientia Fellowship Grant (PS46197), the Cancer Institute NSW Career Development Fellowship (RG243183) funded by the NSW Government, NHMRC Ideas (RG241515), UNSW GRIP Award (PS74064), and the GROW Early Career Academics Grant (PS66730). C.C.N. would like to acknowledge the support from the Science and Technology Scholarship Program for Overseas Study for Master’s and Doctoral Degrees, Vin University, Vingroup, Vietnam. This study was partly conducted at the Australian National Fabrication Facility, NSW Node, a firm founded under the National Collaborative Research Infrastructure Strategy that offers researchers in Australia with nano- and microfabrication capabilities.
The paper, “Development of a Bioinspired Soft Robotic System for Teleoperated Endoscopic Surgery” was published in the journal Cyborg and Bionic Systems on Jun. 12, 2025, at DOI: 10.34133/cbsystems.0289.