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Research Papers

Preliminary Mechanical Characterization of the Small Bowel for In Vivo Robotic Mobility

[+] Author and Article Information
Benjamin S. Terry

Department of Mechanical Engineering,  University of Colorado at Boulder, 427 UCB, 1111 Engineering Drive, Boulder, CO 80309-0427 benjamin.terry@colorado.edu University of Colorado at Denver, 12631 E 14th Avenue, Aurora, CO 80045e-mail: jonathan.schoen@ucdenver.edubenjamin.terry@colorado.edu University of Colorado at Boulder, 427 UCB, 1111 Engineering Drive, Boulder, CO 80309-0427 e-mail: mark.rentschler@colorado.edubenjamin.terry@colorado.edu

Allison B. Lyle

Department of Mechanical Engineering,  University of Colorado at Boulder, 427 UCB, 1111 Engineering Drive, Boulder, CO 80309-0427 allison.lyle@colorado.edu University of Colorado at Denver, 12631 E 14th Avenue, Aurora, CO 80045e-mail: jonathan.schoen@ucdenver.eduallison.lyle@colorado.edu University of Colorado at Boulder, 427 UCB, 1111 Engineering Drive, Boulder, CO 80309-0427 e-mail: mark.rentschler@colorado.eduallison.lyle@colorado.edu

Jonathan A. Schoen, Mark E. Rentschler

Department of Mechanical Engineering,  University of Colorado at Boulder, 427 UCB, 1111 Engineering Drive, Boulder, CO 80309-0427  University of Colorado at Denver, 12631 E 14th Avenue, Aurora, CO 80045e-mail: jonathan.schoen@ucdenver.edu University of Colorado at Boulder, 427 UCB, 1111 Engineering Drive, Boulder, CO 80309-0427 e-mail: mark.rentschler@colorado.edu

J Biomech Eng 133(9), 091010 (Oct 14, 2011) (7 pages) doi:10.1115/1.4005168 History: Received December 21, 2010; Accepted September 19, 2011; Published October 14, 2011

In this work we present test methods, devices, and preliminary results for the mechanical characterization of the small bowel for intra luminal robotic mobility. Both active and passive forces that affect mobility are investigated. Four investigative devices and testing methods to characterize the active and passive forces are presented in this work: (1) a novel manometer and a force sensor array that measure force per cm of axial length generated by the migrating motor complex, (2) a biaxial test apparatus and method for characterizing the biomechanical properties of the duodenum, jejunum, and ileum, (3) a novel in vitro device and protocol designed to measure the energy required to overcome the self-adhesivity of the mucosa, and (4) a novel tribometer that measures the in vivo coefficient of friction between the mucus membrane and the robot surface. The four devices are tested on a single porcine model to validate the approach and protocols. Mean force readings per cm of axial length of intestine that occurred over a 15 min interval in vivo were 1.34 ± 0.14 and 1.18 ± 0.22 N cm−1 in the middle and distal regions, respectively. Based on the biaxial stress/stretch tests, the tissue behaves anisotropically with the circumferential direction being more compliant than the axial direction. The mean work per unit area for mucoseparation of the small bowel is 0.08 ± 0.03 mJ cm−2 . The total energy to overcome mucoadhesion over the entire length of the porcine small bowel is approximately 0.55 J. The mean in vivo coefficient of friction (COF) of a curved 6.97 cm2 polycarbonate sled on live mucosa traveling at 1 mm s−1 is 0.016 ± 0.002. This is slightly lower than the COF on excised tissue, given the same input parameters. We have initiated a comprehensive program and suite of test devices and protocols for mechanically characterizing the small bowel for in vivo mobility. Results show that each of the four protocols and associated test devices has successfully gathered preliminary data to confirm the validity of our test approach.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of the MFS in vivo (left). Cross section of a single MFS balloon segment (right).

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Figure 2

MFS insertion (left) and fully inserted (right) into the jejunal region of the small bowel

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Figure 3

Biaxial test apparatus and intestine sample ready for processing (inset)

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Figure 4

Steps in Mucus Adhesivity Characterization: Tubular intestine sample adhered to lower test mount (A). Upper grip brought into contact with sample (B). Cuts are made through the intestinal wall prior to separation (C). Two halves of the sample are pulled apart while recording force (F) and displacement (s).

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Figure 5

Tribometer with curved specimen tray (left). In vivo tribometer test (right).

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Figure 6

Radial contact force exerted by small bowel on bolus

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Figure 7

Left: stretch-stress results for proximal, middle, and distal tissue samples. Curves that are indicated with an L are stretched along the longitudinal direction, and C indicates the circumferential direction. Right: mean stretch values of all equibiaxial tissue samples at a post-collagen engagement stress level of 53 kPa.

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Figure 8

COF versus sled position for three runs on a single sample (in vitro test, distal small bowel). Inset: portion of an intestine sample illustrating relative size of mucosa topographical features.

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