Towards the development of minimally invasive medical devices for separating the  mesocolon from the retroperitoneum during colorectal surgery

The recent discovery that the mesocolon is one, continuous organ has prompted revaluation of previous literature and drives the design of new instruments to exploit this state of the art discovery intraoperatively. The main hypothesis of this thesis is to innovate laparoscopic surgery by developing a laparoscopic medical device to assist in separation of the mesocolon from the retroperitoneum during surgical procedures which involve colectomy.

The findings of this research indicated that there is unique opportunity to improve laparoscopic surgery, with key focus on the mobilisation of the mesocolon through exploitation of Toldt’s fascia; a bloodless, fascial plane. The gold standard of treatment for colorectal cancer and other bowel diseases such as ulcerative colitisis partial or total colectomy, which involves mobilisation of the mesocolon. This presents an opportunity to design medical devices which can exploit Toldt’s fascia, which adheres the mesocolon to the retroperitoneum, during mobilisation of the colon.

This thesis details the application of a multi-disciplinary approach to medical device design. The four disciplines that contribute to this research are biomedical engineering, human factors, anatomical modelling, and industrial design. Contextual understanding through a literature review and primary research that included surgical observation, laparoscopic video data analysis, modelling of internal anatomical structures, and mechanical characterisation of non-intestinal colorectal tissues informed the design process.

Data in the literature were reviewed to understand the complex and dynamic nature of colorectal laparoscopic surgery. Details on how surgeons process information while conducting surgery were identified, and facilitated the creation of a Human Information Processing model for laparoscopic surgery. As a result, instrument usability could be likened to a laparoscopic surgeon’s already established thought process and skillset.

Constructing 3D anatomical models of the mesocolon and Toldt’s fascia extends the work of previous efforts to enhance the understanding of non-intestinal colorectal structures of the abdomen. Different data sets were used to develop an anatomically accurate model of the mesocolon for education and illustrative purposes. These models reinforced the latest research which characterised the mesocolon as one, continuous organ.

Mechanical characterisation of non-intestinal colorectal tissues of a porcine specimen was undertaken. The tissues characterised were mesocolon, peritoneum, fascia, and small intestinal mesentery. Most notably, fascia and peritoneum are used interchangeably in the literature; however, most recent state of the art research concludes that these are two discrete entities, prompting revaluation of the mechanical characteristics of these tissues. This work was used to determine the upper limit of forces that can be applied to these tissues before failure. This work also forms the foundation for human-porcine tissue comparability testing in the future to determine if porcine tissue can serve as a readily available, analogous tissue for device testing.

The design phase of the research was research-led, and followed a multiple diamond design process. The process was comprised of iterative development cycles along a linear path, and began with a wide scope which became more focused as the concepts became more developed. Concept design underwent an iterative process of expert review and subsequent refinement. Evaluation of the concepts was systematic and dynamic. Each concept was analysed longitudinally at the end of each development cycle. Further developed concepts were tested by a surgical expert on a porcine model to determine their validity. The most successful concepts were then further refined. The patent landscape was examined, which forms a firm foundation for further development of these refined concepts.