Abstract-Percutaneous intervention has attracted significant interest in recent years, but many of today's needles and catheters can only provide limited control of the trajectory between an entry site and soft tissue target. In order to address this fundamental shortcoming in minimally invasive surgery, we describe the first prototype of a bio-inspired multi-part probe able to steer along planar trajectories within a compliant medium by means of a novel "programmable bevel", where the steering angle becomes a function of the offset between interlocked probe segments. A kinematic model of the flexible probe and programmable bevel arrangement is derived. Several parameters of the kinematic model are then calibrated experimentally with a fully functional scaled-up prototype, which is 12 mm in diameter. A closed-loop control strategy with feed-forward and feedback components is then derived and implemented in vitro using an approximate linearization strategy first developed for car-like robots. Experimental results demonstrate satisfactory twodimensional trajectory following of the prototype (0.68 mm tracking error, with 1.45 mm STD) using an electromagnetic position sensor embedded at the tip of the probe.Index Terms-Biologically inspired robots, closed-loop control, medical robots and systems, needle steering, nonholonomic motion planning I. INTRODUCTIONERCUTANEOUS intervention has always attracted significant interest because it is performed through the skin and, as such, it has several advantages for the patient [1]. Tumor biopsy, brachytherapy, deep brain stimulation and localized drug delivery, for instance, benefit from this operative technique to reduce tissue trauma and hospitalization time.In order to localize a lesion, preoperative planning using Computer Tomography (CT) or Magnetic Resonance (MR) Manuscript received May 14, 2010. This work was supported by the EU-FP7 Project ROBOCAST (FP7-ICT-215190) and has also received funding from the European Research Council under the European Union's Seventh Framework Programme (FP7/2007(FP7/ -2013 / ERC grant agreement n° [258642-STING].S. Y. Ko and L. Frasson are with Department of Mechanical Engineering, Imperial College London, SW7 2AZ, UK (e-mail: s.ko@imperial.ac.uk, luca.frasson07@imperial.ac.uk).F. Rodriguez y Baena is with Department of Mechanical Engineering and the Institute of Biomedical Engineering, Imperial College London, SW7 2AZ, UK (corresponding author to provide phone: +44-(0)20-7594-7046; fax: +44-(0)20-7594-1472; e-mail: f.rodriguez@imperial.ac.uk).images is often necessary. If the lesion is reachable through a straight path, a straight rigid needle can be used. For a safe operation, the location of the needle tip can be monitored by means of external markers mounted on the proximal end of the needle by relying on the fixed geometrical relationship between the base and needle point.Recently, there have been efforts to introduce steerable needles in percutaneous interventions where a straight path does not seem possible or is not safe. Steerab...

Current trends in surgical intervention favour a minimally invasive approach, in which complex procedures are performed through very small incisions. Specifically, in neurosurgery there is a need for minimally invasive keyhole access, which conflicts with the lack of manoeuvrability of conventional rigid instruments. In an attempt to address this shortcoming, the current state of progress is reported on a soft-tissue intervention and neurosurgical guide (STING) to access deep brain lesions through curved trajectories. The underlying mechanism of motion, based on the reciprocal movement of interlocked probe segments, is biologically inspired and was designed around the unique features of the ovipositor of certain parasitic wasps. Work to date has focused on probe development, low- and high-level control, and trajectory planning. These aspects are described, together with results on each aspect of the work, including biomimetic microtexturing of the probe surface. Progress is very encouraging and demonstrates that forward motion into soft tissue through a reciprocating mechanism is indeed viable and can be achieved through a suitable combination of microtexturing and microfabrication techniques.

Percutaneous needle insertions are a common part of minimally invasive surgery. However, the insertion process is necessarily disruptive to the substrate. Negative side effects are migration of deep-seated targets and trauma to the surrounding material. Mitigation of these effects is highly desirable, but relies on a detailed understanding of the needle-tissue interactions, which are difficult to capture at a sufficiently high resolution. Here, an adapted Digital Image Correlation (DIC) technique is used to quantify mechanical behaviour at the sliding interface, with resolution of measurement points which is better than 0.5mm, representing a marked improvement over the state of the art. A method for converting the Eulerian description of DIC output to Lagrangian displacements and strains is presented and the method is validated during the simple insertion of a symmetrical needle into a gelatine tissue phantom. The needle is comprised of four axially interlocked quadrants, each with a bevel tip. Tests are performed where the segments are inserted into the phantom simultaneously, or in a cyclic sequence taking inspiration from the unique insertion strategy associated to the ovipositor of certain wasps. Data from around the needle-tissue interface includes local strain variations, material dragged along the needle surface and relaxation of the phantom, which show that the cyclic actuation of individual needle segments is potentially able to mitigate tissue strain and could be used to reduce target migration.

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The ability to steer flexible needles and probes to access deep anatomical locations safely for medical diagnosis and treatment represents a current clinical and engineering research challenge. The behaviour of parasitic wasps has inspired the development of a novel steerable and flexible multi-part probe, which allows the control of its approach angle by adjusting the steering offset between probe segments, i.e. by means of a programmable bevel tip. This paper describes the experimental evaluation of several scaled-up proof-of-concept flexible probe prototypes to explore the effects of tip design (bevel-tip angle) and dimensions (outer diameter) on steering. For each prototype, a linear relationship between steering offset and curvature is confirmed. The effect of probe diameter and bevel-tip angle on steering performance is also analysed, with results confirming that larger bevel-tip angles and smaller probe diameters lead to larger curvature values, although improved steering comes at the price of a less stable insertion process.