Novel self-expanding stent retractors for neuroendoscopy

Thesis

This thesis reports on the development of a novel self-expanding stent retractor (SESR), one that could replace the rigid tubular retractors in common use for minimally invasive neuroendoscopy. The thesis begins with a comprehensive literature review, focusing on existing neuroendoscopy techniques and devices that treat deep brain lesions. The motivation behind this project, including its potential scientific and practical value, is set out clearly. The main body of the thesis describes three different activities.

The first part presents preliminary studies on brain tissue that have been conducted to set up an appropriate medium for SESR deployment. A finite element model of brain tissue phantom was built in Abaqus/Explicit and several surgical scenarios were simulated. The finite element model was validated through comparisons with existing simulation results, data from the literature review and experimental measurements. It is found that the pressure required to create a 16mm diameter corridor in the brain tissue phantom through radial expansion is 2.089 kPa.

The second part of the thesis explains the process of designing and analysing the SESR. Conceptual designs identify the dimensions, materials, and functions of SESR, along with its accessory components. Theoretical analysis found a range for geometric design based on z shape stent radial pressure. Finite element analysis was applied to thoroughly study single z shape stents and SESRs, identifying 5-crown stent SESR (wire diameter 0.31mm to 0.33mm) and 10-crown stent SESR (wire diameter 0.34mm to 0.36mm) to be suitable designs for neuroendoscopy deployment. Finally, prototypes were manufactured and experiments conducted to validate these results of finite element analysis.

The third part of the thesis explores the SESRs' deployment in brain tissue. In both finite element analysis and in vitro experiments, SESRs created access corridors in the brain tissue phantom similar in efficacy to those by rigid tubular retractors, while reducing the pressure on surrounding tissue. By changing SESR’s radial pressure along its longitudinal direction, alternative deployment shapes were also attainable, which suggested suitability for varying surgical needs.

In summary this thesis demonstrates that the proposed novel self-expanding stent retractor is a viable design with potential to reduce tissue damage during surgical use.

Authors: Xia, Y

• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: nitinol; tubular retractor; finite element analysis; neuroendoscopy; self-expanding stent; minimally invasive
• Subjects: Neurosurgery; Mechanical engineering; Medical devices