人工尿道括約筋圧調整バルーンの時間依存性材料疲労：機械的および微視的分析

To assesses the influence of artificial urinary sphincter (AUS) device age on PRB mechanical and microscopic properties. The AUS is a fluid-filled hydraulic system comprised of a urethral cuff, mechanical pump, and pressure regulating balloon (PRB). Material fatigue prior to terminal failure of the PRB can reduce its ability to pressurize the urethral cuff, leading to recurrent urinary incontinence.

Tensile testing was performed on PRBs from 32 previously implanted and 1 new AUS. Stress softening and relaxation testing as well as scanning electron microscopy (SEM) were conducted on a subset of 7 PRBs evenly distributed in age. Data were analyzed using linear regression, Pearson correlation, and repeated measures ANOVA.

AUS device age ranged from 2 months to 17.6 years (median 7.2 years). There was a moderate positive linear correlation between PRB age and stiffness (r=0.68,p<0.01). PRB wall thickness displayed a weak negative correlation with PRB age (r=-0.38,p=0.03). There was no noticeable weakening of the PRB with repeated use over the course of a day, regardless of the time of testing or device age. After SEM, 4 of the 7 PRB specimens revealed fine surface cracks present in their microstructure, which were evident in the 4 oldest specimens.

PRBs exhibit progressive material degradation with age prior to terminal failure, including increased stiffness, decreased wall thickness, and formation of microstructural defects. These findings underscore considering age-related PRB fatigue as a potential cause of declining device performance and support earlier evaluation of PRB replacement in symptomatic patients with recurrent stress urinary incontinence.