Design of an Autoclavable Active Cannula Deployment Device

Concentric tube continuum devices, known as active cannulas, consist of multiple pre-curved elastic tubes that extend telescopically and rotate axially with respect to each other. Through these degrees of freedom, an active cannula presents a dexterous and versatile “tentacle-like” mechanism for accessing targets in minimally invasive surgery. Deploying an active cannula in a practical surgical setting requires a sterilizable device capable of specifying positions and trajectories for each degree of freedom. While robotic devices will likely enable this to be done most efficiently in the future, initial clinical feasibility studies are best undertaken with manual devices. In this paper we present specifications, design and development of a manual (that is, not motorized) active cannula deployment device. INTRODUCTION One of the most common surgical tasks is reaching a specific, predefined location within the human body in order to deliver drugs, perform biopsy or deliver therapy (e.g. thermal ablation) [1,2]. Minimally invasive techniques often utilize needles, which in current clinical practice require a straight access path. Recent developments in needle steering enable curved insertion trajectories and control of needle path [3-7]. A drawback of these devices is that they must be embedded in tissue to steer, and use the tissue itself to enable steering. Thus, needle trajectory models (and hence control techniques) require accurate knowledge of tissue mechanical properties and boundary conditions (see e.g. [8,9]). Obtaining this information with a sufficient level of fidelity is an open research question. Also, incorporating inhomogeneous material properties into needle models is an open research challenge. Lastly, these steerable needles are not able to steer through open space or liquid-filled cavities. These factors in part inspired concentric tube devices, i.e. active cannulas, which provide dexterity in a needle-sized package, without requiring tissue reaction forces in order to steer [10-14]. A second advantage is that the active cannula design permits control of needle shaft shape as well as direction of forward tip progression (most prior steerable needle designs consider only the latter). An active cannula consists of elastic pre-curved tubes that extend telescopically and rotate axially with respect to each other. Figure 1 shows an Active Cannula and its degrees of freedom. Prior work on active cannula actuation units, with the exception of [15-16], has focused on robotic actuation. While robotic devices are desirable in the long-term to coordinate many degrees of freedom rapidly, manual actuation is also desirable for 1) initial clinical proof of concept in human cases (IRB and FDA approval of robotic devices is clearly much more challenging than for manual devices), and 2) cases where Figure 1: A three tube active cannula composed of concentric, pre-curved Nitinol tubes. Each tube provides two degrees of freedom.