Characterising the Mechanical Properties of Large Intestine

This research was carried out to characterise mechanical properties of the large intestine. Assessing the mechanical properties of tissue plays an important role in understanding the links between histological structure and physical properties, physical functioning and normal anatomy. The mechanical properties of large intestine are poorly understood but essential for more accurate characterisation of their behaviour, for example during interaction with surgical instrumentation or devices. This project was set in the context of designing a new robotic colonoscopy device. The aim of this study was to develop and evaluate a robust methodology to characterise the ex-vivo mechanical properties of porcine large intestine tissue and create a database of these properties. In order to study the unique and complex physical properties of the large intestine two common techniques were employed: indentation and tensile stretching. A series of indentation and tensile tests were conducted and the time, strain-rate and strain history dependent responses of porcine large intestine during loading and stress relaxation were observed. Linear and non-linear models were used to analyse the tissue response. The results identified strong dependency of the large intestine mechanical properties to strain-rate and loading history. Tissue preconditioning was also found to be an effective way to stabilise the tissue response in air. Tissue hydration was also found to better preserve the natural state of tissue similar to the in-vivo environment. One of the most important observations was the necessity to produce an appropriate testing protocol for such investigations. Guidelines are proposed to set the requirements for mechanical tissue characterisation. For in-vivo investigation of tissue properties, a system based on measuring acoustic impedance properties of the tissue was successfully designed. Stiffness and tissue relaxation properties of the large intestine were examined using this probe and the results were linked back to the indentation outcomes. This system has the capability to be miniaturised and deployed during conventional colonoscopy or robotic hydro-colonoscopy.