Tissue Engineering of the Urethra: From Bench to Bedside

Off-the-Shelf Implant to Bridge a Urethral Defect: Multicenter 8-Year Journey From Bench to Bed

OBJECTIVE

To engineer an acellular mesh to reconstruct the urethra to replace the current surgical practice of using autologous tissue grafts. Cell based approaches have shown progress. However, these have been associated with high costs and logistical challenges.

MATERIALS AND METHODS

Acellular meshes were engineered using liquid collagen. They underwent in vitro, mechanical and bench testing by surgeons. Sixty-nine male New Zealand rabbits were used to refine the design. The final prototype based on the TissueSpan patented technology was then implanted again in a 2 cm long urethral defect in 9 rabbits and in a 4 cm long defect in 6 dogs.

RESULTS

The TissueSpan technology platform allows for the manufacturing of tubular and rectangular meshes in different diameters and thicknesses. The tubular mesh acted as physical conduit to gap the urethral defect with a patent urethra demonstrated after 1month in both animal models. The mesh was absorbed within 1-3months. Spontaneous urothelial coverage of the mesh and smooth muscle cell migration into the surgical area was demonstrated even in a 4 cm long urethral defect. A first in man clinical trial was subsequently initiated.

CONCLUSION

The acellular mesh may have the potential to be an off-the-shelf product for substitution urethroplasty. Its mechanical properties allow surgeons to easily create a physical conduit while its material properties favor tissue remodeling. A large-scale clinical trial is still required to further confirm the safety, performance, and patient benefit of this new medical device.

The effect of platelet-rich fibrin on the biological properties of urothelial cells

Urethral reconstruction presents a challenging issue in urology, primarily due to the limited availability of alternative materials for repair. The advancement of bioengineering technology has brought new hope to researchers, with a focus on the selection of appropriate biological scaffolds and seed cells. In order to find an ideal alternative material, we used platelet-rich fibrin as the bioscaffold and urothelial cells as the seed cells, meanwhile, we intended to investigate the effect of platelet-rich fibrin on the biological properties of urothelial cells. We transformed and characterised induced pluripotent stem cells into urothelial cells and prepared platelet-rich fibrin. Platelet-rich fibrin was cultured in a complex with urothelial cells to observe the effect of platelet-rich fibrin on the proliferation and migration ability of urothelial cells. The results showed that the induced pluripotent stem cells were successfully transformed into urothelial cells, platelet-rich fibrin was regularly arranged in cords, with platelets and other structures distributed between them, and the proliferation and migration of urothelial cells were significantly increased. These results suggested that platelet-rich fibrin is biocompatible with urothelial cells and it promotes the proliferation and migration of urothelial cells, which lays a good foundation for its use as an alternative material for urethral repair.

Engineered Tissues: A Bright Perspective in Urethral Obstruction Regeneration

Impact Statement The current article examines urethral reconstruction on three fronts: presently available grafts, clinical trials, and preclinical studies. In this context, studies have focused on various types of biomaterial grafts, including natural, synthetic, and decellularized, combined with or without cells or growth factors, aiming to improve outcomes at both clinical and pre-clinical stages. Subsequently, four stages in the commercialization regulatory pathway in urethra engineering were examined, focusing on the commercialization challenges, particularly those associated with urethral products. Finally, the forthcoming challenges in urethra engineering and potential solutions for its enhancement have been explored. [Figure: see text].

The Regenerative Microenvironment of the Tissue Engineering for Urethral Strictures

Urethral stricture caused by various reasons has threatened the quality of life of patients for decades. Traditional reconstruction methods, especially for long-segment injuries, have shown poor outcomes in treating urethral strictures. Tissue engineering for urethral regeneration is an emerging concept in which special designed scaffolds and seed cells are used to promote local urethral regeneration. The scaffolds, seed cells, various factors and the host interact with each other and form the regenerative microenvironment. Among the various interactions involved, vascularization and fibrosis are the most important biological processes during urethral regeneration. Mesenchymal stem cells and induced pluripotent stem cells play special roles in stricture repair and facilitate long-segment urethral regeneration, but they may also induce carcinogenesis and genomic instability during reconstruction. Nevertheless, current technologies, such as genetic engineering, molecular imaging, and exosome extraction, provide us with opportunities to manage seed cell-related regenerative risks. In this review, we described the interactions among seed cells, scaffolds, factors and the host within the regenerative microenvironment, which may help in determining the exact molecular mechanisms involved in urethral stricture regeneration and promoting clinical trials and the application of urethral tissue engineering in patients suffering from urethral stricture.

Biological Macromolecule-Based Scaffolds for Urethra Reconstruction

Urethral reconstruction strategies are limited with many associated drawbacks. In this context, the main challenge is the unavailability of a suitable tissue that can endure urine exposure. However, most of the used tissues in clinical practices are non-specialized grafts that finally fail to prevent urine leakage. Tissue engineering has offered novel solutions to address this dilemma. In this technology, scaffolding biomaterials characteristics are of prime importance. Biological macromolecules are naturally derived polymers that have been extensively studied for various tissue engineering applications. This review discusses the recent advances, applications, and challenges of biological macromolecule-based scaffolds in urethral reconstruction.

Biomimetic Bilayered Scaffolds for Tissue Engineering: From Current Design Strategies to Medical Applications

Tissue damage due to cancer, congenital anomalies, and injuries needs new efficient treatments that allow tissue regeneration. In this context, tissue engineering shows a great potential to restore the native architecture and function of damaged tissues, by combining cells with specific scaffolds. Scaffolds made of natural and/or synthetic polymers and sometimes ceramics play a key role in guiding cell growth and formation of the new tissues. Monolayered scaffolds, which consist of uniform material structure, are reported as not being sufficient to mimic complex biological environment of the tissues. Osteochondral, cutaneous, vascular, and many other tissues all have multilayered structures, therefore multilayered scaffolds seem more advantageous to regenerate these tissues. In this review, recent advances in bilayered scaffolds design applied to regeneration of vascular, bone, cartilage, skin, periodontal, urinary bladder, and tracheal tissues are focused on. After a short introduction on tissue anatomy, composition and fabrication techniques of bilayered scaffolds are explained. Then, experimental results obtained in vitro and in vivo are described, and their limitations are given. Finally, difficulties in scaling up production of bilayer scaffolds and reaching the stage of clinical studies are discussed when multiple scaffold components are used.

[Research advances of three-dimensional bioprinting technology in urinary system tissue engineering]

For the damage and loss of tissues and organs caused by urinary system diseases, the current clinical treatment methods have limitations. Tissue engineering provides a therapeutic method that can replace or regenerate damaged tissues and organs through the research of cells, biological scaffolds and biologically related molecules. As an emerging manufacturing technology, three-dimensional (3D) bioprinting technology can accurately control the biological materials carrying cells, which further promotes the development of tissue engineering. This article reviews the research progress and application of 3D bioprinting technology in tissue engineering of kidney, ureter, bladder, and urethra. Finally, the main current challenges and future prospects are discussed.