The stiff guide

Flexible endoscopes that doctors use to inspect your insides may handle better if they contain elements that can stiffen up at will, says Dr Arjo Loeve.

“Every exit is an entrance,” Dr Arjo Loeve joyfully remarks at the end of his propositions. But, as any gastro-enterologist will testify, pushing a flexible hose up someone’s bum can be a heck of a job. Especially the first S-shaped part is notorious for its sharp turns and its unpredictable anatomy. A flexible hose, which an endoscope, despite all its complexity, basically is, will incidentally buckle up in the curves and be impossible to advance. Pushing harder merely leads to major discomfort for the patient and quite possibly will stretch and damage the large intestine.

No wonder then that multiple researchers have come up with various methods of stiffening an endoscope in order to improve its manoeuvrability. But only four attempts have resulted into scientific publications, and only one of these in a clinical demonstration. “It seems that there is still a lot of work to be done on this subject,” Loeve concludes in his PhD thesis.

He shows how shaft-guidance may be achieved by two elements in a tube that can be stiffened alternatively: the stiffened element serves as a rail supporting the rest of the tube sliding over it. For a next curve, the other element is stiffened up to take over the guiding. The stiffening elements may be arranged parallel on opposite sides of the tube or concentrically, depending on the mechanical realisation.

In his thesis, Loeve compares three different mechanisms for these stiffening elements: vacuum tubes, clamped cables and miracle polymers. The vacuum tubes may be compared to a hard pack of sealed coffee that softens when you break the vacuum. An inflatable balloon inside the tube clamps the steel cables and the materials are selected for maximal friction. Promising, says Loeve, but mechanically complicated and prone to entanglements. His favourite is the stiffening polymer, which has a sharp phase transition at a preset temperature. Heating or cooling elements

within the tube are required to control the stiffness. No prototype has been developed in this study, however. Loeve recommends clamped cables (Forguide) and stiffening polymers (PastoLock) as the way forward for his successors.

Arjo Loeve, ‘Shaft-guidance for flexible endoscopes’, 12 June 2012, PhD supervisors Prof Jenny Dankelman and Dr Paul Breedveld (3mE).

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