Chained Flexible Capsule Endoscope: Unraveling the Conundrum of Size Limitations and Functional Integration for Gastrointestinal Transitivity

TL;DR

The study tackles the gap between diagnostic capsule endoscopes and therapeutic GI interventions by proposing a Chained Flexible Capsule Endoscope (FCE) with a rigid-soft-rigid architecture to extend functional capabilities without enlarging overall size. The design enables passive navigation through the small intestine, magnetically actuated tail propulsion for locomotion, and on-demand expansion via a thermal trigger for anchoring, sampling, or drug delivery, addressing intrinsic volume constraints. Feasibility is demonstrated in in vitro models and ex vivo tissues, showing passable traversal through zigzag lumens and safe navigation around features like a knot, along with expansion/disassembly under high-frequency EM. However, clinical translation requires in vivo validation, safety assessments, and integration of real-time control and localization to enable robust, automated deployment of the therapeutic functions. Overall, the FCE concept provides a promising pathway to functionally enriched, size-compatible capsule endoscopes with potential applications in targeted therapy and tissue interaction within the GI tract.

Abstract

Capsule endoscopes, predominantly serving diagnostic functions, provide lucid internal imagery but are devoid of surgical or therapeutic capabilities. Consequently, despite lesion detection, physicians frequently resort to traditional endoscopic or open surgical procedures for treatment, resulting in more complex, potentially risky interventions. To surmount these limitations, this study introduces a chained flexible capsule endoscope (FCE) design concept, specifically conceived to navigate the inherent volume constraints of capsule endoscopes whilst augmenting their therapeutic functionalities. The FCE's distinctive flexibility originates from a conventional rotating joint design and the incision pattern in the flexible material. In vitro experiments validated the passive navigation ability of the FCE in rugged intestinal tracts. Further, the FCE demonstrates consistent reptile-like peristalsis under the influence of an external magnetic field, and possesses the capability for film expansion and disintegration under high-frequency electromagnetic stimulation. These findings illuminate a promising path toward amplifying the therapeutic capacities of capsule endoscopes without necessitating a size compromise.

Figures (10)

• Figure 1: Design and functionality of the proposed flexible capsule endoscope. (a) Illustration of the challenges faced by longer capsule endoscopes during transit through the narrow, elongated lumen of the small intestine, where their smooth passage is impeded. (b) Schematic representation of the "rigid-soft-rigid" configuration of our flexible capsule endoscope. The first 'rigid' segment is modelled after existing commercial endoscopes, with the 'soft' segment enabling passive deformation under intestinal compression stresses and peristaltic forces, facilitating adaptation to the zigzag environment of the small intestine. (c) The additional rigid section at the tail end of the capsule is designed to induce a worm-like crawling propulsion motion via the interaction of a pair of internal radial magnets under an external magnetic field, and to integrate functional components. The figure also depicts the expansion of the capsule endoscope in response to high-frequency electromagnetic heating, leading to the expansion of an Ecoflex film. This feature suggests potential applications for anchoring, drug delivery, sampling, and scaffold deployment.
• Figure 2: Schematic of the rotary joint in a flexible capsule, constructed with a custom connection mechanism, 3D-printed malleable ring, and iron pins. (b) "Passability" metric used for performance evaluation, where a tethered wire in a curved plastic hose replicates small intestine conditions. Results are summarized in Table 1.(c) Manual bending of the flexible capsule and measurement of extreme bending angle. Despite a stiffness of 70%, the softer, non-hollowed-out components do not cause appreciable deformation, with bending facilitated by the rotary joints and ring deformation. Component lengthening from 18mm to 24mm did not notably increase the bending angle. These findings may inform future design optimizations of flexible capsules.
• Figure 3: Analysis and Modelling of 'Soft' Structure. (a) Shows parametric representation of the structure. (b) Explores material property impact on bending deformation. (c) Presents ANSYS simulation results aligning with experimental data. (d) Indicates lower bending force with higher stiffness, favouring VeroMagenta-V over VeroCyan-V as a connecting material.
• Figure 4: Deformation Analysis of FCE. (a) Shows force analysis with stresses $q_{1}$, $q_{2}$ and reaction forces $\textbf{F}{n1}$ and $\textbf{F}{n2}$. Deforming areas $a_{1}^{'}$ and $a_{2}^{'}$ enable wider bending. (b) Displays passive deformation via iron hold forces and reaction forces $\textbf{F}{n1}^{'}$ and $\textbf{F}{n2}^{'}$ (c). (d) Examines soft section deformation under section moments $\textbf{M}{i}$ and $\textbf{M}{j}$. The moment-curvature relationship is derived from the Euler-Bernoulli beam theory.
• Figure 5: (a) In vitro intestinal passage experiment to assess the passive transport capability of the FCE. (b) Model's interior, constructed from pig small intestine, emulates a true intestinal wall. (c) Depiction of one section of the model. (d) Model's rigid, zigzag-patterned support made of acrylic. (e) Force associated with the passive transit of the FCE along the path, demonstrating an elevated tensile force requirement at large corners and small curvatures, such as points B and D, yet confirming the FCE's effective adaptability to such conditions.