Tissue engineering of urinary bladder and urethra: advances from bench to patients

Abstract

Urinary tract is subjected to many varieties of pathologies since birth including congenital anomalies, trauma, inflammatory lesions, and malignancy. These diseases necessitate the replacement of involved organs and tissues. Shortage of organ donation, problems of immunosuppression, and complications associated with the use of nonnative tissues have urged clinicians and scientists to investigate new therapies, namely, tissue engineering. Tissue engineering follows principles of cell transplantation, materials science, and engineering. Epithelial and muscle cells can be harvested and used for reconstruction of the engineered grafts. These cells must be delivered in a well-organized and differentiated condition because water-seal epithelium and well-oriented muscle layer are needed for proper function of the substitute tissues. Synthetic or natural scaffolds have been used for engineering lower urinary tract. Harnessing autologous cells to produce their own matrix and form scaffolds is a new strategy for engineering bladder and urethra. This self-assembly technique avoids the biosafety and immunological reactions related to the use of biodegradable scaffolds. Autologous equivalents have already been produced for pigs (bladder) and human (urethra and bladder). The purpose of this paper is to present a review for the existing methods of engineering bladder and urethra and to point toward perspectives for their replacement.

Figure 1

(a) Diagram for general architecture and cell layers of urinary bladder and urethra. (b) Diagram for the histology of the urinary bladder.

Figure 2

Strategies for urethral replacement using tissue engineering techniques.

Figure 3

Production of cell-seeded tubular urethral graft using self-assembly technique. (a) After the production of a matrix sheet by fibroblasts, it is rolled to form a tube and urothelial cells are seeded in the lumen. (b) Bioreactor for tubular cell-seeded grafts to stimulate differentiation and formation of watertight mucosal layer.

Figure 4

Mechanical stimuli-induced urothelial differentiation in a human tissue-engineered tubular genitourinary graft. Data from immunofluorescence were raised against the indicated molecule as presented in Cattan et al. [48]; they were analyzed with NIH ImageJ software. In (a) percentage of uroplakin II positive surface relative to the urothelial surface is depicted without stimulation (static) at day 7 (7 d), or day 14 (14 d), or with mechanical stimulation (dynamic) and compared with a native porcine tissue. In (b) similar data are presented for cytokeratin 20 (CK20). In (c) heparan sulphate (Heparan S) positive surface was evaluated compared to stromal surface. In (d) data depict collagen VII (Coll VII) positive pixels relative to the length in pixel of the basal lamina.

Figure 5

General strategy for tissue-engineered urinary bladder.

Figure 6

Production of a vesical equivalent by the self-assembly technique. Vesical equivalent reconstruction can be divided in two major steps. (a) Upper panel: deposition of extracellular matrix to create a manipulatable sheet followed by seeding of urothelial cells. (b) Middle panel: proliferation and differentiation of urothelial cells using a specially designed bioreactor. Bioreactor mimics filling and emptying phases of the bladder. Note that under pressure, vesical equivalent adopts a concave form. (c) Lower panel: self-assembly technique allows production of human reconstructed endothelialized vesical equivalent. (A) Masson's trichrome staining of a slice from a native porcine bladder. (B) Masson's trichrome staining of a slice from a human reconstructed vesical equivalent.