Page 41 - Flexible Robotics in Medicine

24 Chapter 2

examination, while the sigmoid colon segment and sigmoidodescending junction were the
difficult areas to scope as the areas with the frequent iatrogenic perforations and looping
occurring [14]. Thus in this chapter, the methodology for colonoscopy application will
discuss the creation of two components (a straight segment and a bent segment) instead of a
complete colon model. These components model after the rectosigmoid junction angle and
the sigmoid colon segment.

2.3 Methodology

This chapter will first determine the gaits for the soft robot to mimic, discuss the proposed
design based on origami bellows, and select materials for prototyping. It will also cover the
possible application in colonoscopy.

2.3.1 Gait selection

The snake is capable of four types of movements: serpentine, rectilinear, concertina, and
sidewinding. The serpentine movement is the most apparent characteristic of the snake and
is undulatory locomotion that can be used in both land and water, as it contracts muscles
in a way that thrusts its body side to side. The sidewinding movement is a less commonly
observed movement that is employed by the snake to move across terrains that have fewer
resistance points. It advances by contracting and throwing its body sideways, requiring
much fewer points of contact due to the lack of friction, and most of the movement
progression is in midair [22]. These two movement patterns are beneficial for the snake
to be able to move across multiple types of terrains [23]. However, this report mainly
considers rectilinear and concertina locomotion, as these are the movements that are
applicable in moving through an environment like the colon, which is narrow and tubular
with multiple bends and folds.

2.3.1.1 Snake’s rectilinear locomotion

Rectilinear locomotion allows snakes to move in a straight path instead of the serpentine
path that is often associated with snakes. It is achieved by utilizing a combination of the
snake’s scales and muscles near the belly and is more commonly used by more massive
snakes such as pythons and boas.

A snake must use two sets of muscles in order to achieve this gait. First, its anterior oblique
muscles will contract to lift the connecting scale upward and forward so that it can dig
into the ground. Then, the posterior oblique muscles will contract such that the scale gets
pulled backward while its edge is static. The combination of the contractions of these two
opposing muscle groups allows the body segment to be pulling forward. If all segments of