Development of Auxetic Polymeric Stent-graft for the palliative Treatment of Oesophageal Cancer

Oesophageal cancer is the ninth leading cause of malignant cancer death and its prognosis remains poor, ranking as the sixth frequent cause of death in the world. This research work is aimed to use Auxetic (rotating-squares) geometry, only theoretically predicted and analysed by (Grima and Evans 2000), for the production of a novel Auxetic oesophageal stents and stent-grafts relevant to the palliative treatment of oesophageal cancer and also for the prevention of dysphagia. This study also endeavoured to manufacture a significantly small diameter Auxetic oesophageal stent and stent-graft. In order to easily deploy the Auxetic stent orally using a commercial balloon dilatational catheter, and hence it also obviates the need of an expensive dedicated delivery system. A novel manufacturing route was employed in this research to develop both Auxetic films and Auxetic oesophageal stents, which ranged from conventional subtractive techniques to new generative manufacturing methods.
Polyurethane was selected as a material for the fabrication of Auxetic films and Auxetic oesophageal stents because of its good biocompatibility and non-toxicological properties. The Auxetic films were later used for the fabrication of seamed Auxetic oesophageal stents. The flexible polyurethane tubular grafts were also attached to the inner luminal side of the seamless Auxetic oesophageal stents, in order to prevent tumour in-growth. The scanning electron microscopy (SEM) was used to conduct surface morphology study by using different Auxetic specimens developed from different conventional and new additive manufacturing techniques. Tensile testing of the Auxetic films was performed to characterise their mechanical properties. The stent expansion tests of the Auxetic stents were done to analyse the longitudinal extension and radial expansion of the Auxetic stent at a range of radial pressures applied from the balloon catheter, and to also identify the pressure values where the Auxetic stent fails.
Finite element models of both Auxetic film and Auxetic stent were developed, and the results were compared with experimental results with reasonably good agreement. The tensile testing of the Auxetic polyurethane films revealed that the Poisson’s ratio of the sample ranged between -0.87 to -0.963 at different uniaxial tensile load values. From the stent expansion test, it was found that the Auxetic oesophageal stent radially expanded from 0.5 to 5.73mm and longitudinally extended from 0.15 to 1.83mm at a range of applied pressure increments (0.5 to 2.7 bar) from the balloon catheter.