An Artificial Sphincter based on Dielectric Elastomer Actuators in the context of Urinary Incontinence

Urinary incontinence is a prevalent condition that significantly impairs quality of life, particularly among elderly individuals and women. Conventional Artificial Urinary Sphincters (AUS) face limitations in mechanical complexity, reliability, and adaptation to female anatomy. This thesis proposes and investigates a soft actuation approach based on dielectric elastomer actuators (DEAs). The work is structured around three main contributions. First, the mechanical behavior of the urethra was characterized using uniaxial tensile testing on porcine samples along longitudinal and circumferential directions, and published literature data for the human urethra were incorporated. These experiments enabled the development of a fiber-reinforced hyperelastic model capturing the anisotropic and nonlinear response of urethral tissue. The model incorporates fiber modulus, orientation, and volume fraction, achieving normalized RMSEs of 9.24% and 12.98% in the circumferential and longitudinal directions, respectively, outperforming conventional phenomenological models (RMSE > 30%). Second, a soft artificial urethra was developed for ex vivo testing. Among candidate materials including hydrogels, silicones, polyurethanes, and composites, Ecoflex 00-10 (1/8 A: 7/8 B ratio) and PAAm hydrogel closely matched native tissue compliance. Ecoflex exhibited a radial stretch of 1.4 at 5 kPa, compared with 1.32 for the human urethra, and maintained robust, repeatable performance under pressures up to 10 kPa, while PAAm hydrogel was slightly stiffer and limited by dehydration. Third, a modeling and theoretical framework for tubular DEAs was established, accounting for electromechanical coupling and incompressible Yeoh-type hyperelasticity of active and passive layers. Ex vivo testing on artificial urethras demonstrated that DEA-based cuffs functioning as artificial sphincters, with 2 × 200 µm active layers, produced a radial opening of 0.47 mm at an internal pressure of 16 kPa under an electric field of 70 V/µm when the urethra was closed at the distal end. In a free-end configuration, the same cuffs enabled urethral closure up to 8 kPa and reversible radial opening under electric fields up to 70 V/µm, generating flow and demonstrating controlled occlusion and reopening under physiologically relevant pressures. Overall, this thesis advances the understanding of urethral mechanics, provides a reproducible artificial urethra platform, and demonstrates the feasibility of soft DEA-based sphincters, laying the foundation for patient-specific, female-adapted AUS devices.