TISSUE ENGINEERING

                                               

   Tissue engineering may allow the patients 's own cells to be obtained and seeded onto bio- degradable scaffolds that permit the formation of a particular tissue. These tissues can be employed to repair tissue defects caused by disease of trauma. Furthermore, tissue engineering may allow the ex- vivo engineering of tissue by means of  three- dimensional  bioscaffolds seeded  with mature cell or stem cells and cultivation in bioreactors leading to the formation of whole tissues or organs, e.g, liver, heart, cartilage, e.t.c .
    MSCs are good candidates for tissue engineering protocols . Several  scaffolds are currently available and may be classified as biologically derived polymers isolated from extracellular matrix, plants, seaweeds (e.g. hydroxyapatite, tricalcium phosphate, polyactide and polyglycolide) or a combination of both.
     Mesenchymal  stem cells (MSCs)  are characterized by their capacity  for self- renewal and the production of multiple lineages whereas MSCs exist in many other tissues, e.g. skeletal muscle, fat, spinal membrane.
   Embryonic stem cells offer higher pluripotency but remain problematic in clinical use because of ethical issues. In contrast MSCs harvested from adult organisms are ethically uncomplicated and readily available. However , the harvesting of these cells requires  invasive procedures and adult MSCs have poor quality when compared with embryonic stem cells (Baxter et al, 2004; Roura et al, 2006. )
                                                             

    Stem cells with fetal origins have the potential to offer the ideal balance between quality and ethics. Fetal cells from fetal tissue such as umbilical cord, umbilical cord blood or placenta  may  lie in between (Embryonic  and adult ) with respect  to quality and quantity.
     This is an attractive source for clinical applications and more studies should be carried out.
     Polyglycolic  acid nonwoven mesh tubes coated with copolymer solution were seeded with autologous bone marrow derived mononuclear  cells and a living autologous  vascular graft with growth  potential  developed . This is for advancing the field of congenital heart surgery..The currently available synthetic vascular grafts such as PTF  lack growth potential  and present problems related  to biocompatibility including thrombosis , ectopic  calcification and increased susceptibility to infection.
    Due to lack of growth potential  the surgery  needs to be delayed until the patient recipient has grown to a suitable  size to allow for inflammation  of an adult  size graft.
   Tissue engineered graft in the surgical repair of congenital anomalies is cearly  established.
    Mesenchymal  stem cells are an attractive cell source for regenerative  medicine.
      Bone marrow aspirate is obtained from the iliac crest. Synovium is harvested  from the knee joint. Adipose tissue can  be harvested from perinephric  fat tissue. Muscle was harvested  from anterior  tibial muscles.
     Cells from various sources were studied. Synovium and muscle derived cells had a higher  proliferation potential than bone marrow and adipose derived cells.. The  earlier  types had much more chondrogenic potential.
     Transplanting autologous chondrocytes  cultured in collagen  gel has been reported  for the treatment of full thickness  defects  of cartilage.
     Neovascularisation  is a critical step in tissue engineering applications, since implantation of voluminous  grafts without  sufficient vascularity results in hypoxic cell death  of central  tissues. A three dimensional  spheroidal co culture system consisting of human  umbilical vein  endothelial  cells have been developed to improve angiogenesis in tissue engineering.  Human  umbilical vein endothelial  capillary grown in collagen  gels are able to form luminized  capillary like structures and there is stimulatory effect of fibroblasts on endothelial cell sprouting .