Bioinspired Suction Cup Equipped Needle for Minimally Invasive ONSF
Authors:   School of Biomedical Engineering & Imaging Sciences, King's College London, Lovatt-Fraser Joseph , Liu Anhao , da Cruz Lyndon , Bergeles Christos , Hadi Sadati S.M. ,   NIHR Biomedical Research Centre at Moorfields Eye Hospital UCL
Published: September 2024

Optic nerve sheath fenestration (ONSF) is used to treat increased intracranial pressure caused by craniocerebral injury. The operation usually requires the detachment of the eye muscles and cutting open part of the skull to access the nerve behind the eye in the eye orbit [1]. Severe potential complications such as visual loss by making a deep incision that damages the nerve fibres is another challenge with ONSF. To achieve minimally invasive ONSF, we have recently proposed a multi-arm Concentric Tube Robot (CTR), consisting of a camera and a suction cup-equipped needle (called Gripe-Needle) arm (see Fig. 1a) [2], [3]. The compliant miniature size of the robot enables performing ONSF by bypassing the eye globe in the eye orbit through a small collimator (incision port) that is sutured to the eye globe. The Gripe- Needle uniformly and gently grasps the incision area vicinity by suction force. This eliminates the distance between the gripping and incision sites and the challenges with estimating the incision depth due to the resulted complex deformation of the tissue [3]. Ex-vivo evaluation of the earlier design of Gripe-Needle showed successful grasping and manipulation of different porcine eye tissues. However, a successful incision while maintain the optic nerve tissue could not be achieved [3]. In this paper, we revisited the geometry and material properties of the Gripe-Needle to address this issue. Medical suction grippers have been studied extensively for biopsy or tissue handling during surgical interventions [4]. Such devices use an external suction system to provide negative air pressure and can deliver suction forces of up to 5 N. Compared to forceps-type graspers, the suction grippers allow a safer grasp and incision of the target tissue. However, multi-purpose toolsets that combines interventional tools with a suction cup have not extensively explored. The Gripe-Needle design in [3] featured a sticky gel, inspired by octopus suckers to improve the cup vacuum sealing property, on a flat cup surface with a coaxial needle perpendicular to the incision surface. Ex-vivo test with porcine eye samples showed that this design could effectively (with 57-75% success rate) grasp and manipulate different eye tissues such as the muscles, fatty layers, and clean optic nerve surface while safely providing the necessary 0.1-0.15 N gripping force range of an ONSF procedure on porcine eye samples [2]. However, the design proved ineffective in performing an incision during the tissue grip. Furthermore, the needle right angle increased the chance of bypassing the incision site, i.e. between the optic nerve outer sheath and cord bundle cover, causing severe damage to the nerves. This paper presents a curved Gripe-Needle with a 45- deg inclined needle axis w.r.t. the incision surface (see Fig. 1b). The suction cup curved shape improves the gripper performance by encircling the target tissue and better complying with the round surface of the optic nerve. As a result, better sealing of the suction pressure and a larger gripping area could be achieved. The inclined needle axis helps the needle slide under the optic nerve outer sheath, hence reducing the chance of penetration the inner nerve cord layer. Different sticky gel materials, i.e. foam and a silicone type, are tested on stainless steel, rubber, silicone, and thin film plastic surfaces as well as in ex-vivo tests with porcine eye tissue samples to improve the cup sealing properties and gripping force on real tissue. Such a device can find further application in targeted micro-size minimally invasive surgeries by replacing the needle with another interventional tool. The rest of this paper presents the device fabrication, experimental procedures, results, and a brief discussion on the advantages, disadvantages, and future research directions based on the proposed device.