Understanding interactions with human intestinal tissue for capsule endoscopy

This thesis investigates the mechanical and tribological interactions between capsule endoscopy devices and small intestinal tissues, aiming to inform the future design of capsules in order to address persistent challenges such as capsule retention, slippage, and uncontrolled movement. While capsule endoscopy provides a minimally invasive diagnostic alternative to traditional methods, its effectiveness is often hindered by unpredictable frictional behaviour and poor mobility within the gastrointestinal tract. To address these limitations, this study formulates the central research question: Can a novel experimental methodology that simulates the interaction between capsule endoscopy devices and the intestine provide new insights into the tribological behaviour of a sliding capsule, and the effect of different capsule design factors on friction, in order to inform future medical device development?

A multiphase experimental approach was employed, beginning with the mechanical characterization of porcine small intestine tissue under various strain rates. These results informed the development of an ex vivo friction testing platform that simulates capsule–tissue interactions under hydrated conditions. Friction experiments were performed using various lubricants, capsule orientations, loads, speeds, and surface designs.

The experimental studies revealed that (1) porcine tissue exhibits viscoelastic behaviour with rate-dependent stiffness; (2) mucus and PBS both reduce friction, but mucus does not outperform PBS under current conditions; (3) increased normal load reduces the coefficient of friction, likely due to interstitial fluid dynamics; (4) sliding speed correlates positively with friction and (5) ridge design significantly alters friction, with a 2:1 height-to-width ratio yielding the most stable resistance due to enhanced interlocking. These insights provide a foundational framework for future advancements in capsule endoscopy by clarifying the mechanics of frictional interaction within the small intestine.