FEMALE UROLOGY

Mechanical properties of urogynecologic implant materials
Dietz HP, Vancaillie P, Svehla M, Walsh W, Steensma AB, Vancaillie TG
Royal Hospital for Women, New South Wales, Australia
Int Urogynecol J Pelvic Floor Dysfunct. 2003; 14: 239-43

• Synthetic suburethral slings have recently become popular despite the risk of erosion commonly associated with synthetic implants. Some of these materials seem to have unexpectedly low erosion rates. Based on the hypothesis that erosion is due, in part, to biomechanical properties, we undertook an in vitro study. The biomechanical properties of eight non-reabsorbable synthetic implant materials, stiffness (slope, N/mm) and peak load (N) were determined from load vs. displacement curves. Open-weave Prolene mesh showed unique biomechanical properties compared to other tested materials. The tension- free vaginal tape had the lowest initial stiffness (0.23 N/mm), i.e. low resistance to deformation at forces below the elastic limit, whereas the stiffest implant tested, a nylon tape, reached 6.83 N/mm. We concluded that the TVT and other wide-weave Prolene tapes have unique biomechanical characteristics. These properties may be at least partly responsible for the apparent clinical success of the implants
  
  
• Editorial Comment
  The authors review the biomechanical properties of currently popular implant materials used in the treatment of female stress urinary incontinence and pelvic reconstruction. Materials reviewed included polypropylene as well as polyethylene terephthalate (mersilene), expanded polytetrafluoroethylene (Gortex) and nylon. Parameters quantified included initial stiffness (load needed before the material begins irreversible deformation) and the mean peak load at which time the material will rupture. Testing indicated that the tension free vaginal tape was the least stiff of the materials tested.
  The authors utilized a testing system, which is valuable to review for future researchers in this area. It would have been of great value to the reader if the authors had been able to also test the reviewed materials at identical widths; they noted in the report that some specimens were of smaller width than others secondary to their commercial production. The discussion section raises some valuable points regarding the interaction of the graft material on the native tissues and the effect of a biomechanical difference between the two. Though this paper does not comment on the manner of weave and mesh pore size it makes for excellent reading for those interested in the physical properties of these popular synthetic graft materials.

Dr. Steven P. Petrou
Associate Professor of Urology
Mayo Clinic College of Medicine
Jacksonville, Florida, USA