An Automated Intestinal Biomechanics Simulator for Expediting Robotic Capsule Endoscope Development1

Abstract

Robotic capsule endoscopes (RCEs) are pill shaped devices used for noninvasive imaging, chemical sensing, performing simple surgical procedures, and active locomotion through the bowel lumen [1]. Currently, there is no accurate in vitro method for testing RCEs during development, and thus, they are prematurely tested in vivo at a cost of about $1400 per swine test [2]. The purpose of this research was to develop an in vitro method of testing RCEs without the need for repetitive animal experimentation. We have developed a device that simulates the biomechanical behavior and environment of the small intestine to expedite the development of RCEs. This device (Fig. 1Fig. 1Intestine biomechanics simulator with mounted synthetic intestine (not filled)) supports two independently controlled compressive pressure vessels that mimic peristaltic waves and traverse at a speed corresponding to that of human peristaltic waves: 0.08–2 cm/s [3–6]. The simulator was authenticated by calibrating the cavity pressure of the vessels to exert the main components of peristaltic force within human physiological ranges: traction force (4–40 gf) and contact force (80–500 gf). These values ascertain the biomimicry of the simulator and thus allow for experimentation of RCEs. Mounted intestines are kept moist by humidifying the device, thus creating an environmental chamber. The use of such a device will save researchers both time and money in research and development of RCEs, allowing for sooner commercialization of this emerging noninvasive technology.The human intestine propels chyme using peristaltic and segmentation waves. Peristaltic waves advance the chyme while segmentation waves mix it for better nutrient absorption [3]. The main traversing agents of these waves, and thus the focus of the simulator's calibrations, are traction and contact forces. The coalition of these forces allows for wave propagation velocities of 0.08–2 cm/s [3–6]. The intestinal biomechanics simulator was designed to mimic two traversing waves to allow for biomimicry of both peristalsis and segmentation.The simulator (L.6 m × W.3 m × H.3 m) was designed to accommodate a 3.5 cm diameter reusable synthetic intestine (Fig. 2). During experimentation, a synthetic intestine (O-SIN-A-0005, SynDaver, Tampa, FL) is mounted on two cylindrical openings on each end of the tank housing. Though the simulator can operate with a porcine intestine, a synthetic intestine is used for both sanitation purposes and higher resilience to deformity. The synthetic intestine contains preloaded chyme and is validated against mechanical, physic-chemical, thermal, and dielectric properties of the small intestine. The intestine is also compatible with all known surgical devices, including suction devices, which are a component of the RCE testing we are conducting. As with a real intestine, the properties of the model intestine alter if the tissue dries out. To prevent such occurrence, the intestine-holding environmental chamber is held at 100% humidity. A high humidity also decreases external intestine friction and thus minimizes tissue deformation from the pressure vessels' motion, which would not be experienced in vivo.During experimentation, RCEs are inserted automatically via servo motor linkage at one of the openings. This automation allows for minimal user interaction during experimentation to minimize experimental variance. The simulated peristaltic waves traverse via two independently controlled linear actuators consisting of a stepper motor, lead screw, nut, and linear slide. The compression mechanism, referred to as a pressure vessel (Fig. 3), resembles a donut shape solid with an expandable inner wall. The inner layer of the pressure vessel is a polyisoprene tube that expands upon pressure increase. The pressure vessel contains two ports: for air inlet, modulated via 200 kPa dynamic pressure regulator, and pressure transducer (4426-005G, Digi-Key, Thief River Falls, MN) outlet.To ensure biomim