NWO VICI – Dendritic Instruments – Outreaching the Squid

This VICI-research project is funded by the Netherlands Organization for Scientific Research NWO.

Background

In ‘standard’ minimal access surgery, the surgeon inserts rigid instruments through small incisions in the skin or natural orifices to reach targeted areas inside the human body. This approach drastically reduces the invasiveness of surgery compared to conventional open approaches, yet the reduced size of the surgical entry-point does also severely restrict the maneuverability of the used instrumentation. This lack of instrument maneuverability becomes especially apparent when considering Endoscopic Skull Base Surgery (ESBS). A prime target of ESBS are tumors on the pituitary gland positioned at the skull base, the region that separates the brain from the rest of the head. The nose is used as the surgical entry-point, and due to the rigid nature of the used instrumentation, the surgeon needs to create a straight surgical pathway to the pituitary gland. The limited width of this pathway in combination with the need for multiple instruments severely limits sideway movements of the instruments. This situation leads to a phenomenon called swordfighting wherein the shafts of instruments collide and, moreover, it severely restricts the maneuverability of the individual tools (i.e. grasper, scissors, etc.).

We strive to improve on overall instrument maneuverability with the development of dendritic instruments. A dendritic instrument is a maneuverable single-shaft instrument that branches into multiple independently steerable tools. Such an instrument would eliminate the occurrence of swordfighting, as the number or shafts is reduced to one, while providing the surgeon sufficient maneuverability of the individual tools. This research project is divided into two main topics; the mechanical construction and methods of control of dendritic instruments, such that these instruments are able to be implemented in operating theatre in the near future.

Steering

The mechanical construction of a dendritic instrument consists of two basic parts. First, there is the shape memory shaft that should be capable of following a curved trajectory up to the targeted area while providing a stable base. Secondly, there are the individual steerable branches that sprout from this stable base and provide independent maneuverability of each individual tool.

Creating a steerable branch starts with a flexible structure, either containing joints or a compliant backbone. The actuation of such this flexible structure can then be realized by several actuation methods, including the use of electric motors, hydraulic actuators, and shape memory alloys. Our research is focused on a fully mechanical actuation method based on cable-structures. This allows for structures that are easy to miniaturize, eliminates the need for possibly dangerous electric currents, high pressures or high temperatures, and shows high potential for reducing the costs of fabrication.

Besides the obvious requirement that the branches need to be maneuverable, they should also have a certain stiffness in order to cope with external forces that will be present during, for example, tissue manipulation. In our search for a suitable cable-structure to achieve high maneuverability and stiffness, we have developed a cable-structure in which multiple cables are placed at different angles along the longitudinal axis. This structure has already shown great promise and is now in the process of further optimization.

Control

Dendritic instruments consist of many small joints and branches which the surgeon(s) needs to actively steer, in order to perform complex surgical tasks (e.g. suturing or tissue manipulation). The amount of joints in dendritic instruments are even so many, that currently existing prototypes require the cooperation of two surgeons to perform a task which is actually meant for only one surgeon. In other words, dendritic instruments have more Degrees of Freedom (DOF) than any  surgeon can control alone. However, the large amount of DOFs combined with an intuitive method of control is exactly what is required for dendritic instrumentation to become a reality.

The BITE research method to dendritic instrument control is one which is exploration driven. The optimal mechanical construction and DOF configuration are still being researched. Hence, the accompanying control interface or instrument handle cannot be designed yet. To investigate the best methods of control, virtual instruments are simulated in a Virtual Environment (VE). Physical hand movements and gestures are measured with RGB-D Kinect cameras, and mapped to virtual instrument movements. By playing with the coupling between hand DOF and instrument DOF, new control strategies are tested and reverse engineered to ultimately discover the best method for dendritic instrument control.

Dendritic_control_simulation_setup

Image adapted from  www.nimblevr.com (previously www.threegear.com)

I-Flex – Steering Towards Miniaturization Limits

Developed in 2007-2008, diameter 0.9 mm, steering range: ±90º in all directions.

The retina is a light-sensitive layer at the inside of the eye. The macula is the region at the center of the retina with the highest concentration of light-sensitive cells. Macula degeneration – a disease which is a major cause of blindness –  is caused by a disfunctioning choroid layer under the macula. A way to treat macula degeneration is to perform surgery to the choroid layer via a tiny incision in the retina near the macula.  Reaching the choroid layer under the macula is extremely difficult as the surgeon has to operate through the incision under an angle while avoiding damage to the extremely delicate macula layer.  A steerable instrument could potentially solve this issue by making it easier to steer the instrument through the incision.

The largest design and fabrication challenge of such an instrument is the extreme miniaturization of the steerable mechanism in the tip. Down-scaling our patented Cable-Ring mechanism, already applied in the Endo-Periscope III and MicroFlex, to a very small scale, resulted in the  I-Flex – world’s smallest steerable surgical instrument that can be steered in all directions. The compliant tip has a diameter of only  0.9 mm and is constructed from 7 steel cables and a spring. Being equipped with a tiny gripper, the tip can be steered in two Degrees of Freedom (DOF). The instrument contains a novel handle that combines intuitive steering with a fine and precise pincer grip.

Feedback of experienced eye-surgeons from the Eye Hospital in Rotterdam has led to the development of a second prototype which is currently under construction. This instrument incorporates a different handle, allowing further miniaturization of the steerable tip to a diameter of only 0.45 mm – three times the size of a human hair.

 

Publications

Media

Shaft Guidance for Flexible Endoscopes

Flexible endoscopes (long, slender, flexible instruments with a camera and light at the distal end, having working channels to introduce flexible instruments) are used for diagnostic and therapeutic interventions inside the human digestive system and inside the abdomen. Though used for their flexibility, the flexibility of these instruments causes several difficulties during insertion and use. During insertion, flexible endoscopes can buckle and loop, which may hamper full insertion into the patient’s body. During therapeutic interventions, the flexible endoscope fails to provide stability for surgical instruments that are introduced through the flexible endoscope.

Shaft-guidance would be a good solution because it potentially enables following a 3D trajectory without any support of the surrounding anatomy at all. Combining auto-propulsion with a rigidity control mechanism may provide improvement in applications within confined anatomies where auto-propulsion simplifies insertion and rigidifying the endoscope shaft helps to stabilize the instruments during surgery. Three potentially suitable rigidity control concepts are selected and further investigated to quantitatively and qualitatively predict the maximally achievable flexural rigidity of these rigidity control mechanisms:

Vacu-SL

FORGUIDE

PlastoLock

The thesis on this topic can be found on:
Shaft-Guidance for Flexible Endoscopes

 

FORGUIDE

The FORGUIDE mechanism enables making a shaft-guide out of cheap standard parts that is rigidified by creating a laminate that consists of a spring, cables and expandable tube. The connection between these three layers is obtained by friction. The bench tests showed that the FORGUIDE prototype FGP-01 of only 5.5 mm diameter could provide flexural rigidities up to 1541 Ncm2 , which far exceeds the flexural rigidity of flexible endoscopes. Furthermore, a bending radius of almost 1 cm could be achieved in the compliant state with the FGP-01 without losing the ability to rigidify.

MultiFlex – Tentacle from Steel

 

 

Developed in 2008-2009, diameter 5 mm, steering range: ±200º in all directions.

The MultiFlex is what we call a multi-steerable instrument. Based on the Cable-Ring mechanism applied in the Endo-Periscope III, the MultiFlex does not contain just one, but five steering segments serially stacked on top of each other. Each of these segments can be actuated in two Degrees of Freedom (DOF) by its own set of four steering cables, resulting in a total of 20 steering cables and a 10-DOF maneuverable tip capable of making a wide range of 3D shapes and curves. This level of maneuverability gives the instrument the ability to steer around anatomic strucures, making it world’s first instrument of this kind developed at 5 mm dimensions.

By using the Cable-Ring mechanism, all actuation cables could be positioned at the same diameter. Consequently, the increase in maneuverability does not affect the outer diameter of the instrument, which is still equal to Ø5 mm with a complexity similar to the Endo-Periscope III. The control handle of the MultiFlex has a  structure similar to the tip, yet its dimensions are scaled-up for a better fit to the surgeon’s hand.

 

Publications

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Endo-PaC – Endoscopic Path Controller

Developed in 2011-2012.

In the field of minimally invasive surgery and specifically in pathway surgery – i.e. minimally invasive procedures carried out transluminally or through instrument-created pathways – spatial disorientation is a common experience to surgeons.

Our Endo-PaC (Endoscopic Path Controller) is a simulator designed to investigate human control behavior during path following tasks. Emulating the shaft and handle of a maneuverable surgical instrument, Endo-PaC’s hardware controller consists of a base, an instrument shaft, and a handle with a joystick. The hardware controller contains five position sensors to measure the orientation of the shaft relative to the base, the translational displacement of the shaft, and the orientation of the joystick relative to the shaft. Instead of having a separate joystick, the handle can also be directly connected to the joystick, making the Endo-PaC suitable for comparing thumb control with wrist control.

The hardware controller is combined with custom-developed software animating surgical pathway scenarios. This virtual environment enables the assessment of the user performances based on criteria such as task completion time, motion smoothness, collisions, and the length of the travelled path. This makes the Endo-PaC highly suitable for comparing different control techniques.

Publications:

Steerable Guidewire – Maneuvering without Twisting

Developed in 2007-2008, diameter 0.9 mm, length 1 m, steering range: ±90º in all directions.

The Steerable Guidewire has been developed by spin-off DEAM in a very close collaboration with the BITE-group, using our patented Cable-Ring technology. Intended for easy steering through a network of blood vessels during catheter interventions, the guidewire contains a flexible shaft ending in a steerable tip with two Degrees of Freedom (DOF). The mechanism is novel as compared to existing guidewire designs in that it requires no need for twisting the guidewire body for re-directing the tip, which results in a much more stable and fluent 3D steering motion. The tip-mechanism is similar to the I-Fex and composed out of seven steering cables surrounded by a spring. The handle contains two joysticks, one at the proximal handle side and one at the distal handle side, that can both be used to control the 2-DOF tip. The Steerable Guidewire forms the basis for a series of new multi-steerable catheters designs currently being developed in the BITE-group.

 

Publications

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PlastoLock

Flexible endoscopes are used for diagnostic and therapeutic interventions in the human body for their ability to be advanced through tortuous trajectories. However, this very same property causes difficulties as well. For example, during surgery a rigid shaft would be more beneficial since it provides more stability and allows for better surgical accuracy. In order to keep the flexibility and obtain rigidity when needed, a shaft guide with controllable rigidity could be used. On this page we introduce the PlastoLock shaft-guide concept, which uses thermoplastics (Purasorb PLC 7015) that are reversibly switched from rigid to compliant by changing their temperature from 5 to 43 degrees Celcius. These materials were used to make a shaft that can be rendered flexible to follow the flexible endoscope and rigid to guide it.  A feasibility study shows the great potential of this concept in terms of achievable flexural rigidity, miniaturization, and simplicity.

Vacu-SL

In order to fully benefit from the functionalities of flexible endoscopes in surgery, a simple shaft-guide that can be used to support the flexible endoscope shaft is required. Such a shaft-guide must be flexible during insertion into the human body and rigidified when properly positioned to support the flexible endoscope shaft. A shaft-guide called ‘Vacu-SL’ was designed.

The Vacu-SL rigidity control mechanism utilizes the flexural rigidity increase that is achieved by vacuuming foil tubes filled with small particles. In this prototype the influence of particle hardness, size, and shape on the flexural rigidity of vacuumed foil tubes filled with these particles is investigated. Experiments show that the flexural rigidity increases with the hardness and irregularity of the particles and that there may be an optimal particle size in the low particle diameter region.

MicroFlex – Steering at a Micro-Scale

Developed in 2005-2006, diameter 1.3 mm, steering range: ±90º in all directions.

The MicroFlex is a steerable instrument for micro-surgery with a miniature Cable-Ring mechanism consisting of a ring of six steel cables (Ø0.2 mm) surrounded by a spring. The six cables are used for steering the tip, whereas the inner spring is replaced by a central cable that can be used to drive a miniature gripper on the tip (not yet incorporated in this prototype). The result is an instrument that realizes 3D-steering with only seven cables and a spring – smaller and at the same time simpler than existing steerable instruments.

 

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Solving medical problems through nature’s ingenuity