Mesenchymal stem cells, sources of cells and differentiation potential.

Tissue is frequently damaged or lost in injury and disease. There has been an increasing interest in stem cell applications and tissue engineering approaches in surgical practice to deal with damaged or lost tissue. Tissue engineering is an exciting strategy being explored to deal with damaged or lost tissue. It is the science of generating tissue using molecular and cellular techniques, combined with material engineering principles, to replace tissue. This could be in the form of cells with or without matrices. Although there have been developments in almost all surgical disciplines, the greatest advances are being made in orthopaedics, especially in cartilage repair. This is due to many factors including the familiarity with bone marrow derived mesenchymal stem cells and cartilage being a relatively simpler tissue to engineer. Unfortunately significant hurdles remain to be overcome in many areas before tissue engineering becomes more routinely used in clinical practice. Cells used in tissue engineering could be autologous, allogeneic or xenogeneic. The cells could be stem cells or cells further down the differentiation pathway. The use of embryonic stem cells is associated with religious, political and social concerns, but the use of adult stem cells is generally well accepted. Stem cells have been identified in a number of adult tissues, albeit in small numbers. In addition to bone marrow, mesenchymal stem cells have been identified in a number of tissues including adipose tissue and fat pad. The mesenchymal stem cells are generally isolated from the tissue and expanded in culture. These cells can be differentiated down a particular differentiation pathway e.g. osteoblast or chondrocyte, using predefined culture conditions before being used for clinical applications. In this paper stem cells are discussed including their various sources and their differentiation potential.