Design, manufacturing and characterisation of a wireless flexible pressure sensor system for the monitoring of the gastro-intestinal tract
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Ingestible motility capsule (IMC) endoscopy holds a strong potential in providing advanced diagnostic capabilities within the small intestine with higher patient tolerance for pathologies such as irritable bowel syndrome, gastroparesis and chronic abdominal amongst others. Currently state-of-the art IMCs are limited by the use of obstructive off-the-shelf sensing modules that are unable to provide multi-site tactile monitoring of the Gastro-Intestinal tract. In this work a novel 12 mm in diameter by 30 mm in length IMC is presented that utilises custom-built flexible, thin-film, biocompatible, wireless and highly sensitive tactile pressure sensors arrays functionalising the capsule shell. The 150 μm thick, microstructured, PDMS flexible passive pressure sensors are wirelessly powered and interrogated, and are capable of detecting pressure values ranging from 0.1 kPa up to 30 kPa with a 0.1 kPa resolution. A novel bottom-up wafer-scale microfabrication process is presented which enables the development of these ultra-dense, self-aligned, scalable and uniquely addressable flexible wireless sensors with high yield (>80%). This thesis also presents an innovative metallisation microfabrication process on soft-elastomeric substrates capable to withstand without failure of the tracks 180o bending, folding and iterative deformation such as to allow conformable mapping of these sensors. A custom-built and low-cost reflectometer system was also designed, built and tested within the capsule that can provide a fast (100 ms) and accurate extraction (±0.1 kPa) of their response. In vitro and in vivo characterisation of the developed IMC device is also presented, facilitated respectively via the use of a biomimetic phantom gut and via live porcine subjects. The capsule device was found to successfully capture respiration, low-amplitude and peristaltic motility of the GI tract from multiple sites of the capsule.