Bioengineering Approaches for Bladder Regeneration

Abstract

Current clinical strategies for bladder reconstruction or substitution are associated to serious problems. Therefore, new alternative approaches are becoming more and more necessary. The purpose of this work is to review the state of the art of the current bioengineering advances and obstacles reported in bladder regeneration. Tissue bladder engineering requires an ideal engineered bladder scaffold composed of a biocompatible material suitable to sustain the mechanical forces necessary for bladder filling and emptying. In addition, an engineered bladder needs to reconstruct a compliant muscular wall and a highly specialized urothelium, well-orchestrated under control of autonomic and sensory innervations. Bioreactors play a very important role allowing cell growth and specialization into a tissue-engineered vascular construct within a physiological environment. Bioprinting technology is rapidly progressing, achieving the generation of custom-made structural supports using an increasing number of different polymers as ink with a high capacity of reproducibility. Although many promising results have been achieved, few of them have been tested with clinical success. This lack of satisfactory applications is a good reason to discourage researchers in this field and explains, somehow, the limited high-impact scientific production in this area during the last decade, emphasizing that still much more progress is required before bioengineered bladders become a commonplace in the clinical setting.

Keywords: bioreactors; bladder regeneration; c; regenerative medicine; scaffolds; stem cells.

Figure 1

Urinary bladder histological organization in physiological conditions. (I–IV) Representative images of a longitudinal bladder section from an adult male rat after trichromic Masson staining. The adventitious layer (the outermost one), the urothelium (II), and the muscle bundles (IV) are stained in dark red, and the extracellular matrix of the submucosa is stained in blue (III). The location of the layers II, III, and IV is shown in image I by a corresponding colored frame with a dashed line; V: The illustration on the right shows the bladder organization in layers. Starting from the lumen, the bladder is composed of a transitional epithelium or urothelium formed by 4–5 layers of specialized cells supported by the basal lamina and followed by the submucosa coat, a loose connective tissue containing fibroblasts, blood vessels, and extracellular matrix and enriched in collagen I and III. Below, consecutive layers with perpendicular orientations of smooth muscle fibers form an inner muscle layer followed by the detrusor, characterized by smooth muscle fibers organized in circular and longitudinal layers. The adventitious layer of adipose tissue completes the structural organization.

Figure 2

Types of urinary diversion currently performed after radical cystectomy: (a) abdominal diversion, such as an ureterocutaneostomy, colonic, or ileal conduit; (b) various forms of a continent pouch created using different segments of the gastrointestinal system and a cutaneous stoma; and (c) orthotopic urinary diversion with an intestinal segment with spherical configuration and anastomosis to the urethra (neobladder, orthotopic bladder substitution).

Figure 3

Acellular bladder submucosa scaffolds. Scanning electron micrographs (SEM) of fresh bladder submucosa (BSM) at 1000× magnification: surface (a) and cross section (b,c). The scale bar indicates 200 µm. Reprinted with permission from Elsevier Ltd., Liu et al. [58].

Figure 4

Morphology of a poly(ε-caprolactone (PCL)/poly-l-lactide (PLLA) scaffold and cell distribution by SEM. Non-woven and randomly oriented fibers of PCL and PLLA at 500× (A) and 5000× (B) magnifications; (C) Urothelial cells on the scaffold surface preserving their phenotype by creating their typical colonies; (D) Bladder smooth muscle cells expanded and proliferated on the scaffold. Reprinted with permission from Elsevier Ltd., Shakhssalim et al. [47].

Figure 5

In vitro bioreactor: a computer senses the pressure in pressure chamber (B) by feedback via a pressure transducer (E). A computer interface establishes and maintains a specific hydrodynamic pressure by controlling a pump (A) output. A pressure valve (C) is almost completely closed to simulate bladder outlet obstruction. Dulbecco’s modified Eagle’s medium with 10% fetal bovine serum was used. The arrows indicate the flow direction. (D) Fluid reservoir. Reprinted with permission from Elsevier Ltd., Chen et al. [50].

Figure 6

In vivo bioreactor: seeded scaffold preparation (A–C) and implantation (D) in the omentum. Reprinted with permission from Elsevier Ltd., Baumert et al. [147].

Figure 7

Bioprinting technologies: components of laser-induced forward transfer (a), inkjet printing (b) and robotic dispensing (c). Adapted from John Wiley and Sons, Malda et al. [163].