Chapter 069. Tissue Engineering (Part 3) Table 69-2 Tissue-Engineering Products in Clinical Trials TRC (Aastrom) Autologous adult bone marrow cells for bone grafting LiverX2000 (Algenix) Extracorporeal liver assist device Encapsulated proliferated islet (Amcyte) Encapsulated islet cells Myocell (Bioheart) Encapsulated cells for myocardial infarction BioSeed-C, BioSeed- Oral Bone (Biotissue Technologies) Autologous tissue repair for bone and cartilage E-matrix (Encelle) Repair or regeneration of disea sed or damaged tissue MarkII (Excorp) Extracorporeal liver assist device ICX-PRO, ICX- TRC (Intercytex) Wound repair and hair regeneration HuCNS- SC (Stem Cell Inc) Human central nervous system stem cells NT-501 (Neurotech SA) Encapsulated cell technology for long- term delivery of therapeutic factors to retina Procord (Proneuron) Autologous activated macrophage therapy for patients with acute complete spinal cord injury ChondroCelect (Tigenix) Autologous chondrocyte implantation Spheramine (Titan Pharmaceutical) Retinal pigment epithelial cells in microcarriers to provide continuous source of dopamine in the brain ELAD (Vigagen) Extracorporeal liver assist device Challenges to Tissue Engineering The greatest success in tissue engineering to date has been in tissues such as skin and cartilage where the requirements for nutrients and oxygen are relatively low. Due to oxygen diffusion limitations, the maximal thickness of an engineered tissue is 150–200 µm if there is not an intrinsic capillary network. Strategies used to overcome this limitation include transplantation of the tissue directly into the patient's vasculature or trying to induce angiogenesis by incorporating growth factors such as vascular endothelial cell growth factor into the scaffold. A more recent approach involves the creation of an intrinsic network of vascular channels immediately adjacent to the engineered tissue. A combination of microelectro mechanical systems (MEMS) fabrication technology and computational models of fractal branching allows the construction of an intrinsic microvascular network scaffold within a biocompatible polymer. This preformed capillary-like network can be seeded with cells and ultimately sustains the growth and function of complex three-dimensional tissues. Immune rejection of allogenic cells is another major obstacle. The use of immunosuppressive drugs is not considered an optimal solution to this problem. One potential solution is to develop "universal donor" cells by masking the histocompatibility proteins on the cell surface. Off-the-shelf availability will need to be addressed for tissue engineering products to be used widely. Ideally, products should be reproducible and available at a wide variety of hospitals, including those without sophisticated facilities for cell culture and cell proliferation. Further Readings Ahsan T, Nerem RM: Bioengineered tissues: The science, the technology, and the industry. Orthod Craniofacial Res 8:134, 2005 [PMID: 16022714] Lavik E, Langer R: Tissue engineering: Current st ate and perspectives. Appl Microbiol Biotechnol 65:1, 2004 [PMID: 15221227] Lysaght MJ, Hazlehurst AL: Tissue engineering: The end of the beginning. Tissue Engineering 10:12, 2004 Sheih SJ, Vacanti JP: State-of-the- art tissue engineering: From tissue engineering to organ building. Surgery 137:1, 2005 Yow KH et al: Tissue engineering of vascular conduits. Br J Surg 93(6):652, 2006 [PMID: 16703652] . Chapter 069. Tissue Engineering (Part 3) Table 69-2 Tissue- Engineering Products in Clinical Trials TRC (Aastrom) Autologous. MJ, Hazlehurst AL: Tissue engineering: The end of the beginning. Tissue Engineering 10:12, 2004 Sheih SJ, Vacanti JP: State-of-the- art tissue engineering: From tissue engineering to organ. (Vigagen) Extracorporeal liver assist device Challenges to Tissue Engineering The greatest success in tissue engineering to date has been in tissues such as skin and cartilage where the requirements