Research Papers

Development of a Variable Stiffness Over Tube Based on Low-Melting-Point-Alloy for Endoscopic Surgery

[+] Author and Article Information
Ruzhen Zhao

State Key Laboratory of Mechanical
Systems and Vibration,
Institute of Biomedical Manufacturing and
Life Quality Engineering,
School of Mechanical Engineering,
Shanghai Jiao Tong University,
800 Dong Chuan Road,
Shanghai 200240, China
e-mail: deep-dimples@sjtu.edu.cn

Yao Yao

State Key Laboratory of Mechanical
Systems and Vibration,
Institute of Biomedical Manufacturing and
Life Quality Engineering,
School of Mechanical Engineering,
Shanghai Jiao Tong University,
800 Dong Chuan Road,
Shanghai 200240, China
e-mail: yaoyaorz@sjtu.edu.cn

Yun Luo

State Key Laboratory of
Mechanical Systems and Vibration,
Institute of Biomedical Manufacturing and
Life Quality Engineering,
School of Mechanical Engineering,
Shanghai Jiao Tong University,
800 Dong Chuan Road,
Shanghai 200240, China
e-mail: luoyun@sjtu.edu.cn

1Corresponding author.

Manuscript received April 27, 2015; final manuscript received February 1, 2016; published online May 12, 2016. Assoc. Editor: Rafael V. Davalos.

J. Med. Devices 10(2), 021002 (May 12, 2016) (8 pages) Paper No: MED-15-1173; doi: 10.1115/1.4032813 History: Received April 27, 2015; Revised February 01, 2016

Instruments used in endoscopic surgery (colonoscopy surgery or natural orifice transluminal endoscopic surgery (NOTES)) are flexible to be advanced in human body. However, when the end of the instrument reaches the target, the instrument should be rigid enough to hold its shape against external forces for better surgical accuracy. In order to obtain these two properties, a variable stiffness over tube based on low-melting-point-alloy (LMPA) is proposed in this paper. The structure exploits the phase transformation property of the LMPA which enables the stiffness change of the over tube by heating and cooling. A prototype was fabricated using a special molding method, and experiments were carried out to evaluate its variable stiffness property and response characteristics. According to experimental results, it costs 17 s to make the over tube transform from rigid state to flexible state and 18 s to make the over tube transform from flexible state to rigid state. The experimental results also indicated that the over tube is very rigid in rigid state and flexible in compliant state. A heat insulation layer was assembled to prevent human tissue from thermal damage. The temperature of the outer wall of the over tube was 42.5 °C when hot water of 80 °C was pumped into the over tube continually with the help of the heat insulation layer.

Copyright © 2016 by ASME
Topics: Stiffness , Surgery
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Fig. 1

Schematic of flexibility and passive bending effects for surgery with flexible endoscope. Endoscope buckling and excessive squeeze to body cavity inner wall occurred when forces were applied to push (a) or pull (b) lesion tissue.

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Fig. 2

Illustration of the variable stiffness over tube

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Fig. 3

Dimension of the Cerrolow 117-tension test specimen

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Fig. 4

Elastic modulus measurement of Cerrolow 117 using tensile test: (a) experimental setup and (b) stress–strain curve

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Fig. 5

Molding process of a segment of the variable stiffness over tube

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Fig. 6

An experimental setup for measuring the flexural stiffness (a) and the axial stiffness (b) of the over tube under rigid state

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Fig. 7

An experimental setup for measuring the deflection of the over tube during state transformation process

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Fig. 8

An experimental setup for measuring transformation times between rigid and flexible state

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Fig. 9

Evaluation results of the flexural stiffness (a) and the axial stiffness (b) of the over tube under rigid state

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Fig. 10

Evaluation results of the flexural stiffness of the over tube under compliant state

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Fig. 11

Evaluation results of the deflection of the over tube during phase transformation process: (a) deflection of the over tube when the water temperature rose from 37 °C to 50 °C and (b) deflection of the over tube when the water temperature was set to 50 °C

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Fig. 12

The water temperature controlled course

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Fig. 13

Evaluation results of the transformation time between rigid state and flexible state: (a) from rigid state to compliant state and (b) from compliant state to rigid state

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Fig. 14

Experimental setup for evaluation of the effectiveness of the heat insulation layer

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Fig. 15

Evaluation results of the effectiveness of the heat insulation layer




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