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Design Innovation

Polymer Rigidity Control for Endoscopic Shaft-Guide ‘Plastolock’ — A Feasibility Study

[+] Author and Article Information
Arjo J. Loeve

Department of Biomechanical Engineering, Faculty of Mechanical, Maritime, and Materials Engineering, Delft University of Technology, Mekelweg 2, 2628 CD Delft, The Netherlandsa.j.loeve@tudelft.nl

Johannes H. Bosma, Paul Breedveld, Dimitra Dodou, Jenny Dankelman

Department of Biomechanical Engineering, Faculty of Mechanical, Maritime, and Materials Engineering, Delft University of Technology, Mekelweg 2, 2628 CD Delft, The Netherlands

J. Med. Devices 4(4), 045001 (Oct 12, 2010) (6 pages) doi:10.1115/1.4002494 History: Received May 03, 2010; Revised August 12, 2010; Published October 12, 2010; Online October 12, 2010

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 it allows for better surgical accuracy. In order to keep the flexibility and to obtain the rigidity when needed, a shaft-guide with controllable rigidity could be used. In this article, we introduce the plastolock shaft-guide concept, which uses thermoplastics that are reversibly switched from rigid to compliant by changing their temperatures from 5°C to 43°C. These materials are used to make a shaft that can be rendered flexible to follow the flexible endoscope and rigid to guide it. To find polymers that are suitable for the plastolock concept, an extensive database and internet search was performed. The results suggest that many suitable materials are available or can be custom synthesized to meet the requirements. The thermoplastic polymer Purasorb® PLC 7015 was obtained and a dynamic mechanical analysis showed that it is suitable for the plastolock concept. A simple production test indicated that this material is suitable for prototyping by molding. Overall, the results in this article show that the plastolock concept can offer simple, scalable solutions for medical situations that desire stiffness at one instance and flexibility at another.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Example of flexibility effects during surgery with a flexible endoscope. (a) Flexible endoscope inserted through the esophagus and an incision in the stomach wall. (b) Reality: Forces applied to pull tissue make the flexible endoscope shaft move. (c) Desired: Endoscope shaft provides stability and tissue is pulled toward the endoscope.

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Figure 2

Variations of the plastolock concept. (a) Plastolock rod concept: A thermoplastic rod can slide inside the flexible endoscope shaft. The rigidity of the rod can be altered at will by heating or cooling the rod material. (b) Plastolock overtube concept: Similar to the plastolock rod but shaped as a tube that slides over the flexible endoscope shaft. (c) Possible cross section of a plastolock rod with heat carrying fluid channels in it. (d) Possible cross section of a plastolock overtube with heat carrying fluid channels in it.

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Figure 3

Temperature-stiffness plot for a (partly) amorphous polymer. Tg is the glass-transition temperature.

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Figure 4

Scheme of the search criteria, sources, and methods used to find suitable polymers for the plastolock concept

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Figure 5

Molding test with Purasorb® PLC 7015. (a) Teflon® mold made at Delft University of Technology workshop demo. The mold consists of two semicylinders, an axis to create the channel of the tube and two caps with vent holes holding the mold parts together. (b) Produced tube (5×7×90 mm3) in straight, rigid condition carrying 305 g weight. (c) Tube is flexible after flushing with warm water. (d) Tube is put in an arch shape and made rigid again by flushing it with cold water. Again carrying 305 g. (e) Tube is put around a 4 mm diameter flexible endoscope, then bent and rigidified in an arch shape. After that, the endoscope was advanced through the tube.

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Figure 6

Damping (tan δ) and storage modulus (E′) of Purasorb® PLC 7015 and PLC/PLG 60/40 for six different frequencies measured from approximately −20°C to 60°C. The plots show the raw data without interpolation as measured with the DMA analyzer. The white background areas indicate the temperature range of 5–43°C.

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