Shaft-Guidance for Flexible Endoscopes

Shaft-Guidance for Flexible Endoscopes

Loeve, A.J.

Dankelman, J. (promotor)

Mechanical, Maritime and Materials Engineering

BioMechanical Engineering

2012-06-12

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. In this thesis, firstly, the fundamental mechanical causes of the difficulties that accompany the use of flexible endoscopes are analysed. Next, an extensive, categorizing review explores the available and potentially suitable solutions to causes of the flexibility-induced difficulties in flexible endoscopy. The review suggests that passive guiding of the flexible endoscope shaft using guides with rigidity control is the most feasible solution. 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. The first investigated rigidity control mechanism (“Vacu-SL” mechanism) utilizes the flexural rigidity increase that is achieved by vacuuming foil tubes filled with small particles. The thesis proceeds with experiments on the influence of particle hardness, size, and shape on the flexural rigidity of vacuumed foil tubes filled with these particles. The experiments showed 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. Next, a mechanism using friction between a rubber tube, stainless steel cables, and a stainless steel spring ( “FORGUIDE mechanism”) is presented, as well as a mathematical model predicting the maximally achievable flexural rigidity of that mechanism. The results of that chapter suggest that there is great potential for improvement of the FORGUIDE mechanism and that this mechanism may very well provide sufficient support for flexible endoscopes. A chapter on the static friction between several kinds of rubber and several types of stainless steel cables aids to advise on how the flexural rigidity of the friction-based FORGUIDE mechanism can be increased by properly choosing the materials of the tube, cables, and spring. The third rigidity control mechanism ( “PlastoLock” mechanism) changes rigidity by heating and cooling a lactide-based polymer through its glass-transition. A feasibility study shows the great potential of this concept in terms of achievable flexural rigidity, miniaturization, and simplicity. Finally, the thesis presents a force analysis and a number of functional design considerations that should guide the further design of a new generation of flexible endoscopes with passively guided shafts. The discussion of the thesis advises on what rigidity control mechanisms are most likely to provide a proper solution for what application areas, and on what steps should be taken next to finally obtain a good solution to the current flexibility-induced difficulties in flexible endoscopy. It is concluded that the FORGUIDE mechanism and the PlastoLock mechanism are most suitable for application in flexible endoscopes for the gastrointestinal tract. These mechanisms are simple, provide high flexural rigidity (especially when considering their size), and may be applied in a very broad range of applications. Many improvements in existing applications and a broadening of the diagnostic and therapeutic possibilities in gastrointestinal health care may be achieved by further developing the investigated rigidity control mechanisms into fully functional guided instruments. Arjo Loeve, 2012

shaft-guidance
flexible endoscopy
colonoscopy
instrument design
endoscopy

http://resolver.tudelft.nl/uuid:f1f3782a-98b3-4e9a-b79a-00b210aecee3

2012-05-29

978-94-6191-329-6

Institutional Repository

doctoral thesis

(c) 2012 Loeve, A.J.