Development and Simulation-Based Validation of Biodegradable 3D-Printed Cog Threads for Pelvic Organ Prolapse Repair

Abstract

Pelvic organ prolapse (POP) is a prevalent condition, affecting women all over the world, and is commonly treated through surgical interventions that present limitations such as recurrence or complications associated with synthetic meshes. In this study, biodegradable poly(ϵ-caprolactone) (PCL) cog threads are proposed as a minimally invasive alternative for vaginal wall reinforcement. A custom cutting tool was developed to fabricate threads with varying barb angles (90°, 75°, 60°, and 45°), which were produced via Melt Electrowriting. Their mechanical behavior was assessed through uniaxial tensile tests and validated using finite element simulations. The results showed that barb orientation had minimal influence on tensile performance. In simulations of anterior vaginal wall deformation under cough pressure, all cog thread configurations significantly reduced displacement in the damaged tissue model, achieving values comparable to or even lower than those of healthy tissue. A ball burst simulation using an anatomically accurate model further demonstrated a 13% increase in reaction force with cog thread reinforcement. Despite fabrication limitations, this study supports the biomechanical potential of 3D-printed PCL cog threads for POP treatment, and lays the groundwork for future in vivo validation.

Keywords: biodegradable cog threads; finite element analysis (FEA); pelvic organ prolapse (POP); vaginal wall reinforcement.

Figure 1

(a) Commercial cog thread model 4D-1W-18 G R (cannula); (b) Representative stress–strain curve of commercial cog thread, highlighting its mechanical response under uniaxial tensile loading (adapted from [13]).

Figure 2

(a) Cutting tool positioned at a 90° angle; (b) cutting tool positioned at a 60° angle; (c) complete tool used for making cuts in the threads.

Figure 3

(a) Microscopic analysis of the cut; (b) a magnified view showing two 90° cuts on the thread, made at distinct positions and orientations; (c) the experimental setup for the uniaxial mechanical characterization of cog threads; (d) representative examples of the cog thread types evaluated in the uniaxial tensile tests.

Figure 4

(a) The developed computational models of cog threads; (b) a 3D computational model of the pelvic cavity of an asymptomatic woman. (1) rectum; (2) uterus; (3) bladder; (4) symphysis pubis; (5) pelvic fascia; (6) arcus tendineous fasciae pelvis; (7) LAM; (8) USLs; (9) CLs [16]. (c) A simplified computational model of the pelvic cavity considered in this study.

Figure 5

Stress–strain curves for healthy and 50% damaged anterior vaginal wall.

Figure 6

Uniaxial tensile test results of cog threads: (a) experimental stress–strain curves; (b) numerical stress–strain curves.

Figure 7

The magnitude of displacement (in mm) of the anterior vaginal wall under a pressure of 160 cmH₂O is shown for (a) the healthy model without cog threads, (b) the damaged model without cog threads, and (c) the damaged model reinforced with cog threads with a 45° cutting angle. Warmer colors indicate higher displacement, while cooler colors correspond to lower displacement.

Figure 8

Force–displacement curves obtained for simulations with and without cog thread reinforcement. Solid line: vaginal wall reinforced with cog threads; dashed line: without reinforcement.