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

Abstract

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 cm(2) 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.

Experimental investigation of intestinal frictional resistance in the starting process of the capsule robot

“…Now one of the main limitations that the capsule robot moves in the intestine inefficiently is the imperfection of the friction model due to the presence of complex lumen surface features and a highly motile, tortuous intestine path. The frictional resistance comes from intestinal peristaltic contractions, mucoadhesion, the collapsed lumen and the interaction between the capsule surface and the intestinal inwall [17]. The surrounding organs, weight of the intestinal wall and pressure from the fluid within the intestine also impart forces on the capsule robot.…”

Sensorless Estimation of the Planar Distal Shape of a Tip-Actuated Endoscope

“…To validate the evaluate the effect of environmental friction on the method, the friction of the simulation model was increased by a factor of 5 (from 0.1 to 0.5) while all other model parameters were unchanged which resulted in the following errors: e baseline = 1.00 ± 0.04 and e est = 0.37 ± 0.03. For reference, Terry et al reported a coefficient of friction of 0.016 ± 0.002 in vivo between tissue and polycarbonate [23].…”

A wirelessly powered expanding-extending robotic capsule endoscope for human intestine

“…It has a coefficient of friction on the order of 10 -3 to 10 -4 ; this makes the locomotion infeasible which exploits effective friction. 20,21 Inchworm-like locomotion that utilizes the intestinal tract's characteristic of compliance helps the device adapt to the special environment. The simple inchworm-like mechanism consists of two radial motion mechanisms (RMM) for expanding the intestinal tract and an axial motion mechanism (AMM) for the robot's elongation.…”