Artificial sphincters: An overview from existing devices to novel technologies

Artificial sphincters (ASs) are used to replace the function of the biological sphincters in case of severe urinary and fecal incontinence (UI and FI), and gastroesophageal reflux disease (GERD). The design of ASs is established on different mechanisms, e.g., magnetic forces or hydraulic pressure, with the final goal to achieve a implantable and durable AS. In clinical practice, the implantation of in-commerce AS is considered a reasonable solution, despite the sub-optimal clinical outcomes. The failure of these surgeries is due to the malfunction of the devices (between 46 and 51%) or the side effects on the biological tissues (more than 38%), such as infection and atrophy. Concentrating on this latter characteristic, particular attention has been given to the interaction between the biological tissues and AS, pointing out the closing mechanism around the duct and the effect on the tissues. To analyze this aspect, an overview of existing commercial/ready-on-market ASs for GERD, UI, and FI, together with the clinical outcomes available from the in-commerce AS, is given. Moreover, this invited review discusses ongoing developments and future research pathways for creating novel ASs. The application of engineering principles and design concepts to medicine enhances the quality of healthcare and improves patient outcomes. In this context, computational methods represent an innovative solution in the design of ASs, proving data on the occlusive force and pressure necessary to guarantee occlusion and avoid tissue damage, considering the coupling between different device sizes and individual variability.