Tissue engineering technologies: just a quick note about transplantation of bioengineered donor trachea and augmentation cystoplasty by de novo engineered bladder tissue.

Tissue engineering technologies: just a quick note about transplantation of bioengineered donor trachea and augmentation cystoplasty by de novo engineered bladder tissue. C. Alberti Tissue engineering is a multidisciplinary scientific field that aims at manufacturing in vitro biological substitutes to enhance or replace failing human organs. Various types of biodegradable synthetic polymer (polyglycolic acid, PGA; polylactic acid, PLA; polylactic-coglycolic acid), naturally-derived (alginate, collagen), acellular tissue-made up (small intestinal submucosa, SIS; acellular bladder submucosa, ABS) and composite (PGA bound to collagen) materials have been used as scaffold for either "unseeded" (cell-free) or "seeded" (autologous cells seeded onto the matrix) tissue engineering strategies. The unseeded technique is directed at promoting the in vivo tissue regenerative process, unfortunately with certain limitations, whereas the "seeded technique" aims at creating in vitro functional replacement tissues or organs. Recently, a decellularized human dead donor trachea has been used as scaffold, that was then seeded, in vitro, by recipient epithelial cells and mesenchymal stem cell-derived chondrocytes, to obtain a bioengineered airway to replace recipient's failing left main bronchus. As far as clinical applications in Urology are concerned, a cell-based approach (PGA-collagen composite scaffold seeded with autologous cells) has been achieved to successfully carry-out an augmentation cystoplasty in subjects with end-stage neuropathic high pressure/poorly compliant bladder. The use of autologous cells, wherein a specimen of tissue is harvested by biopsy from the host, avoids the risk of rejection. Nevertheless, the use of adult organ-specific cells shows many limitations, such as difficulties in their harvesting (potential complications associated with invasive biopsies) and their low proliferative ability. Therefore, various populations of either embryonic or adult stem cells and progenitor cells have been studied as useful cell sources for the tissue engineering. Bioreactors are essential in such technologies, both providing chemo-physical cell culture dynamic conditions, that mimic the in vivo environment, and allowing the assessment of responses of biological substitutes to different biochemical signals and mechanical forces.