Design and Miniaturization of an Ultra-Fine Multi-Degree-of-Freedom Robotic Instrument for Ophthalmic Minimally Invasive Microsurgery

Minimally invasive surgery (MIS) has transformed surgical practice by reducing patient trauma and improving postoperative outcomes. In laparoscopic surgery, these benefits have been further enhanced by the clinical adoption of teleoperated robotic systems, most notably the da Vinci Surgical System, which provides improved dexterity, motion scaling, and ergonomics in confined environments. As surgical robotics advances, its application is expected to extend beyond conventional MIS to microsurgical procedures requiring levels of precision and stability beyond those achievable manually. However, the clinical adoption of robotic assistance in microsurgery remains limited, particularly for minimally invasive procedures in highly constrained workspaces. Teleoperated leader–follower robotic architectures offer a promising solution for robot-assisted minimally invasive microsurgery (MIMS) by enabling precise motion scaling and tremor suppression while preserving intuitive surgeon control. Ophthalmic MIMS requires dexterous manipulation within an extremely confined intraocular workspace under millinewton-level interaction forces. Although snake-like and continuum instruments have been explored to improve access and distal dexterity, achieving multi-degree-of-freedom (DOF) motion within a submillimeter outer diameter remains challenging. These challenges stem from inherent trade-offs among bending range, shaft stiffness, wire routing, pretension, and buckling stability. This work presents the design and miniaturization of an ultra-fine multi-DOF robotic instrument for vitreoretinal surgery. The proposed instrument integrates 2-DOF distal bending (pitch and yaw), shaft rotation (roll), and a microgripper within a 0.7 mm outer diameter. To support miniaturization while maintaining manufacturability and structural integrity, a novel surface-constrained, V-type disk-stacked bending mechanism is introduced. Wire passability through reduced-diameter guide holes is geometrically verified at maximum disk tilt, and shaft stiffness and Euler buckling are analyzed using second-moment-of-area models under a conservative 10 mN lateral tip load. Prototypes with outer diameters of 0.9 mm and 0.7 mm were fabricated and tested. The 0.7 mm instrument demonstrated smooth pitch–yaw bending and reliable grasping, with bending hysteresis of approximately ± 5°. Shaft deflection during bending and grasping remained below 0.06 mm, while rotational whirling produced displacement amplitudes of 0.1–0.23 mm. These results highlight key design trade-offs and provide experimentally validated guidelines for the development of ultra-fine robotic instruments for ophthalmic MIMS.