Engineering of pre-vascularized urethral patch with muscle flaps and hypoxia-activated hUCMSCs improves its therapeutic outcome

Tissue engineering has brought new hopes for urethral reconstruction. However, the absence of pre-vascularization and the subsequent degradation of materials often lead to the failure of in vivo application. In this study, with the assistance of hypoxia-activated human umbilical cord mesenchymal stem cells (hUCMSCs), pedicled muscle flaps were used as materials and pre-incubated in ventral penile subcutaneous cavity of rabbit for 3 weeks to prepare a pre-vascularized urethral construct. We found that small vessels and muscle fibres were scattered in the construct after 3 weeks' pre-incubation. The construct presented a fibrous reticular structure, which was similar to that of the corpus spongiosum under microscope examination. The produced constructs were then used as a patch graft for reconstruction of the defective rabbit urethra (experimental group), natural muscular patch was used as control (control group). Twelve weeks after the reconstructive surgery, urethrography and urethroscope inspections showed wide calibres of the reconstructed urethra in the experimental group. Histopathological studies revealed that fibrous connective tissues and abundant muscle fibres constituted the main body of the patch-grafted urethra. In contrast, in the control group, only adipose tissue was found in the stenosis-reconstructed urethra, replacing the originally grafted muscular tissue. To our knowledge, this is the first report that successfully constructed a pre-vascularized urethral construct by using hypoxia-activated hUCMSC and pedicled muscle flaps. More importantly, the pre-vascularized construct showed a good performance in urethral reconstruction when applied in vivo. The study provided a novel strategy for tissue engineering of pre-vascularized urethral construct for the defective urethra, representing a further advancement in urethral reconstruction.