Partial tissue Engineered bladders are the next step in bladder treatment. In this treatment an entire bladder is grown in vitro on a bladder shaped scaffold made of biodegradable PGA (polyglycolic acid) and PLGA (poly-DL-lactide-co-glycolide) or a combination of PGA and collagen. This scaffold is designed to degrade in the body, after providing a shape to the growing bladder. Autologous urothelial and muscle cells are harvested from the patients bladder, and grown on opposite sides of the scaffold in vitro. When this bladder is implanted in the body, it essentially becomes a natural part of the body. Capillaries grow through the scaffold, giving the new bladder a blood supply. In one study these bladders were implanted into dogs. In a postoperative examination, conducted 4 weeks after implantation, these bladders had a trilayer of urothelium, submucosa, and muscle, and “structurally and functionally, they were indistinguishable from native bladders.” Tissue engineered bladders offer a treatment to bladder disease with none of the drawbacks of the 3 previously described methods.
Cells for culture can be obtained by a 1-2 cm square biopsy of the patient. The tissue is then microsected and the mucosal and muscular layers are separated. The retrieved smooth muscle cells (SMCs) and urothelial cells (UCs) are then cultured separately.
UCs are dissected and plated with serum-free growth medium containing 5ml/mg of epidermal growth factor and 50µg/ml of bovine pituitary extract. SMCs are processed in Dulbeco's modified Eagle's medium with 10% fetal calf serum. The cells are incubated and humidified in an atmosphere chamber containing 5% CO2 at 37°C. The cells are expanded on 70, 15 cm diameter plates of each cell type to obtain approximately 107 cells per plate for the human neo-bladder. The cells are then washed, trypsonized, and collected as pellet. The cells are now ready to be seeded onto the scaffold. Approximate time from biopsy to implantation is 7 weeks for the human neo-bladder.
Three categories of biomaterials are used for engineering genitourinary tissue. These categories are naturally derived materials, acellular tissue matrices, and synthetic polymers. Naturally derived materials include things like alginate, a polysaccharide derived from seaweed, and collagen, one of the most abundant structural proteins in the body. Acellular tissue matrices are created by removing cells from tissues, and are generally collagen-rich. Synthetic polymers are not naturally occurring materials, and include many alpha-hydroxy acids like PGA, PLA, and PLGA. A common theme among biomaterials among the mentioned biomaterials is the fact that they dissolve when they are implanted in the body. This is an important attribute, as they are replaced by the body's tissues once they are in the body.
One of the best examples of a tissue engineering scaffold for the bladder is that of Dr. Anthony Atala, one of the leading figures in the field of tissue engineering. His scaffold is designed to provide the tissue with a blood supply, give the artificial bladder with shape, and degrade once it is implanted in the body. Blood supply is provided by a network of channels and pores. Shape is provided by the materials used, a combination of PGA and collagen. Both of these materials degrade in the body and are replaced by the body’s tissues.
Three types of bladder implants were used in Atala’s bladder trial. The most successful of these was a composite collagen PGA scaffold with an omental wrap. The three patients in which this was implanted went on experience significant improvements in bladder capacity, leak point pressure, and compliance. In postoperative studies, the difference between the composite matrix-based engineered segments were virtually indistinguishable from segments from the original bladder.
The most important aspect of the tissue engineered bladder is the
fact that it includes layers made up of urothelial cells and smooth
muscle cells, much like the human bladder. This quality is achieved
by seeding the sides of the scaffold with cultures of autologous urothelial and
muscle cells. The first step of cell seeding involves harvesting these
autologous cells from the patient. These cells are then grown in
separate cultures, until the necessary number of cells is grown.
When this number is reached, the cells are seeded on the scaffold.
The urothelial cells are then distributed on the inside of the
bladder scaffold, while the muscle cells are distributed on the
outside of the scaffold. These cells are allowed to proliferate, and
eventually result in a bladder with the urothelial and muscle layers.
Atala’s artificial bladder does not replace the original bladder, it augments it. In the implantation procedure an incision is cut in the patient’s midsection. An incision is made in the bladder after access is established. Two catheters are then inserted into the body, one which exits into the original bladder, and one which exits through the urethra. After this is completed, the tissue engineered bladder is anastomosed to original bladder, using polyglycolic sutures and fibrin glue.
Atala A, Bauer SB, Sokerv S, J. J. Yoo, Retik AB. Tissue-engineered autologous bladders for patients needing cystoplasty . Lancet 2006; 367: 1241-46
Oberpenning F, Meng J, Yoo JJ, Atala A. De novo reconstitution of a
functional mammalian urinary bladder by tissue engineering.
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Yoo JJ, Meng J, Oberpenning F, Atala A. Bladder augmentation using
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