Mesenchymal Stem Cell-Based Bone Engineering for Bone Regeneration

Many people worldwide suffer from bone defects due to trauma or disease. About 5-10% of football injury-related bone fractures, in addition to bone tumor resection and massive traumatic bone loss result in critical–sized bone defects that cannot regenerate autonomously (Cattermole et al., 1996; Low et al., 2004; Reuss et al., 2007 as cited in Porter et al., 2009). Usually small bone defects heal spontaneously but large defects cannot regenerate without intervention. There are several options for the reconstruction of large bone defects that include bone grafts (autograft, allograft and xenograft) as well as bone constructs created by bone tissue engineering principles. Among these different strategies, bone grafts from healthy donors have been used as therapies for decades, but nowadays they are used less due to inherent limitations associated with their application. For example, autografts are usually obtained from the iliac crest (Porter et al., 2009) and have been used in clinics for a long time. However some disadvantages, including supply limitation, risk of donor site morbidity, pain, paresthesia, hematoma and inflammation, as well as the need for prolonged rehabilitation (For review see Heary et al., 2002; Krelow et al., 2007; Maddela et al., 2010; Nakajima et al., 2007) limit their applications. Allografts, on the other hand, are the other option that may be chosen for bone defect regeneration. This type of bone graft can be derived from viable or sterilized non-viable (cadaver) human sources. Orthopedic allografts exhibit certain drawbacks by transmitting donor pathogens to the recipient body and triggering host immune responses (For review see Hou et al., 2005 and Nishida et al., 2008). Xenografts obtained from nonhuman sources may be considered as the other alternative for reconstructing bone defects, but this is a last resort which may be taken because it is not an approved option in transplantation, owing to the obvious risk of viral and disease transmission, infection, toxicity and immunogenicity as well as rejection by the recipient’s body (For review see Laurencin et al., 2008; Yang et al., 2007). Concerns associated with applications of bone graft for critical size bone defects have challenged scientists to search for suitable options. Attempts to replace appropriate substitutes for bone graft have resulted in opening a new window in modern regenerative biomedicine and the emergence of bone constructs elaborated by tissue engineering principles. The term tissue engineering is defined as the application of the principles and