A Soft Pneumatic Inchworm Double balloon (SPID) for colonoscopy

Abstract

The design of a smart robot for colonoscopy is challenging because of the limited available space, slippery internal surfaces, and tortuous 3D shape of the human colon. Locomotion forces applied by an endoscopic robot may damage the colonic wall and/or cause pain and discomfort to patients. This study reports a Soft Pneumatic Inchworm Double balloon (SPID) mini-robot for colonoscopy consisting of two balloons connected by a 3 degrees of freedom soft pneumatic actuator. SPID has an external diameter of 18 mm, a total length of 60 mm, and weighs 10 g. The balloons provide anchorage into the colonic wall for a bio-inspired inchworm locomotion. The proposed design reduces the pressure applied to the colonic wall and consequently pain and discomfort during the procedure. The mini-robot has been tested in a deformable plastic colon phantom of similar shape and dimensions to the human anatomy, exhibiting efficient locomotion by its ability to deform and negotiate flexures and bends. The mini-robot is made of elastomer and constructed from 3D printed components, hence with low production costs essential for a disposable device.

Figure 1

SPID design: (a) perspective view with the distal and proximal balloon activated; (b) cross-sectional showing the available inner space of the balloons and the SPA; (c) five steps bio-inspired locomotion, where (i) t_PB–A is the time needed to activate the proximal balloon, (ii) t_SPA–A is the time to activate the SPA in line with the orientation of the colonic lumen, (iii) t_DB–A is the activation time of the distal balloon providing anchorage, (iv) t_PB–D is the deactivation time of the proximal balloon, and (v) t_SPA–D is the deactivation time of the SPA to move it forward.

Figure 2

Experiment results of the balloon with radial expansion reporting external diameter vs. air volume (a), activation air pressure vs. air volume (b), activation air pressure vs. external balloon diameter (c). Static forces and pressures of the balloon inside the colon wall involved resulting from the inchworm locomotion are shown in the top-right section of sub-fig. (d). Sub-figure (e) shows maximal anchorage force that increased with the volume of air exerting 7.9 N with internal pressure of 6.1 kPa.

Figure 3

Sub-fig. (a) shows cross-section of the SPA with 3 chambers, C₁, C₂, C₃, and their forces, F_C1, F_C2, F_C3. Cross-section A − A′, (b), shows the force produced by 1 chamber, C₁, during negative bending. Cross-section B − B′, (c), shows the activation of the 2 chambers during positive bending. Experiments of the SPA unrestricted activation when 1 chamber (d,e) and 2 chambers (f,g) are activated. Sub-fig. (d,f) show the bending angle and the cross-section with the chamber activated in blue. Sub-fig. (e,g) show the position of the tip in the X-Z plane. Sub-fig. (h) shows the vertical extension when 3 chambers are activated and the air pressure thereof in sub-fig. (i).

Figure 4

Sub-fig. (a) shows experiments of the SPA activation force with its extension up to 30 mm. Sub-fig. (b) shows the force produced when the SPA is activated, blue line, and when deactivated, red line.

Figure 5

Experiments of SPID in a vertical tube (a), showing the ability of the two balloons to adapt their diameters to different sections. Sub-fig. (b) shows SPID in different sections of the plastic colon. Videos of these experiments are included in the Supplementary Material V1 and V2.