Male urethral strictures affect approximately 0.6% of the population. Following injury, infection, or radiation therapy, urinary extravasation drives spongiofibrosis, i.e. fibrosis of the corpus spongiosum underlying the urothelial epithelium. Current repair relies on autologous grafts from the buccal mucosa or preputial skin, which restore the epithelial lining but not the vascularised supporting bed, contributing to stricture recurrence. Tissue-engineered grafts offer a promising alternative, but their design first requires a deeper understanding of healthy and diseased urethral tissues. This study aims to fill this gap by mapping the biomechanical and cellular landscape of the male urethra tissues in health and spongiofibrosis, and to obtain new knowledge on the underlying mechanisms contributing to urethral dysfunction. This information will guide the development of biofabrication approaches for functional urethral grafts.

Penile segments of healthy and spongiofibrotic human urethral tissue were collected from gender-affirming surgery (n=1), donor body program (n=2), and urethroplasty (n=2). Comparative analysis of structure, compositional, and mechanical properties were performed on each tissue. Spatial distribution of cells and extracellular matrix components was assessed by immunohistochemistry and immunofluorescence. Collagen fibril organisation and cell morphology were examined by transmission electron microscopy, and tissue architecture and porosity by nano-computed tomography. Mechanical properties were assessed at the macro-scale by dynamic mechanical analysis (tensile, stress-relaxation and creep-recovery modes, n=9 for each measurement) and at the micro-scale by microindentation. A device to measure pressure-diameter relationships ex vivo was developed and first validated on hare urethra.

Fibrotic urethral tissue shows a thickened epithelium with disrupted tight junctions (Figure 1, ZO-1), and greater smooth muscle content (αSMA) compared to healthy controls. Reduced CD31 expression indicates decreased vascular density. Altered collagen type I:III ratio[1], as well as higher collagen density and fibrillar reorganization observed by electron microscopy (Figure 2), are correlated with increased Young's modulus and stress relaxation (p<0.001) in both longitudinal and circumferential orientations. The pressure-diameter device for ex vivo pressure-diameter measurements was validated on hare urethra, which reached a maximal intraluminal pressure of 3.3 kPa.

Major changes occur during spongiofibrosis at both cellular and tissue scales. Decreased CD31+ vessel density indicates microvascular rarefaction, contributing to progressive fibrosis. Epithelial thickening and increased αSMA expression reflect urothelial hyperplasia and myofibroblast activation, hallmarks of progressive ECM remodelling, suggesting endothelial to mesenchymal transition. The increased fibrillar anisotropy and density in fibrotic tissue result in a more elastic tissue. The maximal intraluminal pressure of 3.3 kPa measured in hare urethra falls within the human urethral pressure range during voiding[2], supporting its relevance for testing with human tissue in the upcoming months.

Spongiofibrosis induces significant changes in urethral tissue composition and mechanical behaviour. The proposed characterisation framework informs the design of biomechanically relevant tissue-engineered urethral grafts.

Baskin LS et al. Biochemical characterization and quantitation of the collagenous components of urethral stricture tissue. J Urol. 1993; 150:642-647. doi: 10.1016/s0022-5347(17)35572-6.
Griffiths DJ. Hydrodynamics of male micturition—I Theory of steady flow through elastic-walled tubes. Med. & biol. Engng. 1971; 9: 581–588 (1971). doi: 10.1007/BF02474637

Continence 19S (2026) 102591
DOI: 10.1016/j.cont.2026.102591