A concentric tube-based 4-DOF puncturing needle with a novel miniaturized actuation system for vitrectomy

Abstract

Background: Vitreoretinal surgeries require precise, dexterous, and steady instruments for operation in delicate parts of the eye. Robotics has presented solutions for many vitreoretinal surgical problems, but, in a few operations, the available tools are still not dexterous enough to carry out procedures with minimum trauma to patients. Vitrectomy is one of those procedures and requires some dexterous instruments to replace straight ones for better navigation to affected sides inside the eyeball.

Method: In this paper, we propose a new vein puncturing solution with a 4-DOF motion to increase the workspace inside the eye. A two-member concentric tube-based 25G needle is proposed whose shape is optimized. To operate the concentric tube needle, a novel and miniaturized actuation system is proposed that uses hollow shaft motors for the first time. The presented prototype of actuation system has a stroke of 100 mm in a small size of 148 × 25 × 65 mm (L × W × H), suitable for approaching distant positions inside the eyeball.

Results: Experimental results validate that the targeting accuracy of the needle is less than one millimeter and the needle tip can apply a force of 23.51 mN which is enough to perform puncturing. Furthermore, the proposed needle covers maximum workspace of around 128.5° inside the eyeball. For the actuation system, experiments show that it can produce repeatable motions with accuracy in submillimeter.

Conclusion: The proposed needle system can navigate to the sites which are difficult to approach by currently available straight tools requiring reinsertions. Along with the miniaturized actuation system, this work is expected to improve the outcome of vitrectomy with safe and accurate navigation.

Keywords: Concentric tube robots (CTR); Ophthalmic surgery; Puncturing needle; Vitrectomy.

Fig. 1

Schematic diagram of the motion of the presented pre-bent tool vs the conventional straight one inside the eyeball; a advantage of the bendable tool; b limitations of a straight tool

Fig. 2

Feasibility of proposed needle system in different conditions; a developed prototype with a 10 KRW coin for size reference (10KRW coin has a diameter of 22.86 mm). The inset view shows the puncturing tip on the 25G stylet, b movement of needle inside the eyeball of skull phantom to reach different targets from the same insertion point, c the proposed needle system inside a phantom eyeball, and d movement of the needle inside a block that is filled with albumen (white part of the egg)

Fig. 3

Optimized shape of the needle; a total shape, b cannula, and c stylet

Fig. 4

Developed prototype of the hollow shaft motor-based actuation system; a 3D model and b developed prototype

Fig. 5

Experimental setup; a control setup for experimentations, b experimental setup to validate accuracy and repeatability of the actuation system

Fig. 6

Repeatability experiments; a illustration of the movement used for repeatability experiments and b repeatability error plot in each module of the actuation system

Fig. 7

Experimental setup for targeting accuracy experiments for the needle. Inset view shows the final moved shape

Fig. 8

Real-time movement of the needle to reach target points

Fig. 9

Workspace covered by the needle; a isometric view and b top view

Fig. 10

Geometrical method used for the calculation of the sweeping angle

Fig. 11

Maximum force generated by the puncturing tip only by the movement of the stylet. Inset view shows the contact point of the stylet tip with the load cell sensor (the load cell provides values in gram-force)