Computational tools for the investigation of the mechanical interaction between the urethra and artificial urinary sphincters

The current Thesis presents a novel in silico procedure designed to address limitations in traditional approval processes for artificial urinary sphincters (AUSs). Utilising finite element method (FEM) analysis, the research investigated the mechanical stimulation exerted by the AUS on urethral tissue across its operational phases. Key mechanical fields—compressive strain, compressive stress and hydrostatic pressure—were assessed to evaluate the device’s reliability when the AUS applied a target occlusive pressure, focusing on the most stimulated urethral section. The procedure also evaluated the device’s performance as the sphincter’s ability to maintain continence under simulated urine conditions. Therefore, reliability and performance parameters were derived by the procedure for each AUS under investigation. The initial implementation involved the gold standard device, AMS 800™, assessing its interaction with urethral tissue at clinical occlusive pressure levels. These analyses also helped the tuning of the FEM analysis settings to optimise computational cost and accuracy. Variations in inflation speeds were tested, revealing no significant impact on mechanical stimulation or device’s performance, leading to the selection of the highest speed for efficiency. Subsequent analyses compared the effects of different urethral lumen shapes, with similar outcomes observed between a histological and a simpler elliptical shape. This consistency justified the use of the elliptical shape in further simulations, simplifying the model and reducing computational costs. The following implementation concerned a novel AUS patented by the University of Padua, characterised by a cylindrical design aimed at optimising occlusive pressure distribution. Various device configurations were tested by varying chamber length, chamber thickness and chamber-band clearance and evaluating different material sets for mechanical characterisation. The analyses revealed that chamber length had the most significant impact on device’s reliability and performance, with the longest chamber showing the lowest values in terms of compressive strain and the shortest chamber exhibiting reduced levels of both compressive stress and hydrostatic pressure. Variations in chamber thickness and chamber-band clearance had minimal impact on device’s performance, although they affected the evaluation of the reliability in terms of compressive strain, with the minimum chamber thickness and the maximum chamber-band clearance yielding the lowest values. The study also explored the impact of variations in urethral tissue mechanical properties. Tissue compressibility significantly influenced device’s reliability, with the lowest Poisson’s ratio adopted for the urethral tissue resulting in the highest compressive strain values and lowest hydrostatic pressure values. These findings highlighted the importance of integrating in silico methodologies into AUS approval processes to thoroughly evaluate device’s reliability across diverse scenarios, including ageing. The developed computational tools are intended to aid biomedical industries in the initial device design phase, addressing experimental and ethical challenges, screening multiple configurations and identifying optimal designs for further testing. These tools aim to support clinical practices by improving AUS implantation efficacy and patient outcomes. Future work will involve experimental testing of device prototypes in interaction with a tissue-mimicking phantom under fluido-dynamic conditions and expanding the procedure to assess artificial sphincters for other anatomical dysfunctions. This flexible approach adapts to a wide range of clinical scenarios, advancing the field of artificial sphincters.