Progress on Bionic Artificial Anal Sphincters Based on the Physiological Defecation Mechanism

Fecal incontinence (FI) severely affects physical and psychological well-being. Artificial anal sphincters (AASs) provide a reconstructive option for patients with severe sphincter damage or congenital dysfunctions, but their clinical application is often limited by complications stemming largely from poor biomechanical compatibility with host tissues. This review examines the physiological mechanisms of defecation as the basis for bionic AAS design and classifies existing devices into two main types: those simulating anorectal angle regulation and those mimicking direct sphincter occlusion. A comparative analysis reveals distinct biomechanical failure modes associated with each approach: angle-modulating devices face challenges like tissue hyperplasia around moving parts, while direct occlusion devices, particularly high-pressure circumferential cuffs, frequently lead to tissue erosion, infection, and mechanical breakdown due to ischemic pressure. Addressing this core issue of biomechanical incompatibility is paramount. Novel mechanical designs, such as constant-force mechanisms, aim to mitigate pressure-induced injury. Furthermore, future optimization directions include enhancing device intelligence through smart sensing and AI algorithms, and exploring biohybrid designs that integrate tissue-engineered components to potentially achieve superior long-term integration. This review underscores that harmonizing mechanical function with the biological environment is critical for improving the safety, efficacy, and longevity of AASs in FI treatment.