**2. Mesenchymal stem cells seeded for bone tissue engineering**

MSCs are stromal stem cells that are heterogeneous and are derived from several tissue sources that include adipose tissue [6], periodontal ligaments [7], bone marrow (**Figure 1**) [8], umbilical cord (UC) [9], placenta [10], and lungs [11]. MSCs express surface markers like CD73, CD44, CD90, and CD105. The most widely known and used MSCs are bone marrow MSCs and adipose tissue-derived MSCs isolated and purified from the bone marrow and adipose tissue, respectively. Briefly, the anatomy of the bone marrow is made up of the parenchyma and the stroma part. The parenchyma houses the hematopoietic stem cells, and the stoma part consists of the bone marrow stromal cells (MSCs) that have the capability to differentiate into several cell lines like osteoblasts, chondrocytes, adipocytes, etc. The clinical use of both bone-derived mesenchymal stem cells and adipose stem cells in bone tissue engineering has been reported using various models of bone regeneration such as osteogenesis [12, 13], long bone defects [14, 15], and calvarial defects [16, 17]. Furthermore, co-administration of stem cells with cytokines has been reported to be efficient in bone repair as cytokines and growth factors like stromal derived factor-1 (SDF-1) can lead to increased migration and homing of stem cells to the defected site [18]. In a similar report by Ho et al., they demonstrated that co-administration of stromal-derived factor-1 with BM-MSCs would indirectly enhance bone repair by improving migration of innate cells to the site of bone fracture. They concluded that BM-MSCs overexpressing SDF-1 were efficient in improving the new bone formation during the early stage of fracture healing compared to BM-MSC treatment alone [19]. Genes implicated in fracture healing such as osterix [20], hypoxia-inducible factor-1 [21], and BMP-7 [22] have all been reported to be efficient in bone formation when transfected with MSCs.

**3. Advances in MSCs and tissue engineering technology**

seeded scaffold into a highly vascularized bed. Adapted from [26] with copyright permission.

the non-seeded calcium phosphate scaffold.

Recently, bone tissue engineering in combination with novel stem cell-based technologies is yielding promising results as reported by Syed-Picard and colleagues in their experimental study that BM-MSC-derived cell sheets could be used to fabricate functional periosteal tissue [23]. Briefly, culturing BM-MSCs to hyperconfluence to produce abundant extracellular matrix to form robust cell sheets generated the BM-MSC-derived cell sheets. The authors reported that the generated cell sheets supported with calcium phosphate pellets were transplanted subcutaneously into mice for 8 weeks. They concluded that there was significant bone-like tissue formation by the BM-MSC-calcium phosphate pellet structure compared to

**Figure 1.** Showing in vivo and in vitro stem cell application in engineered tissue (a) In vitro prevascularization methods induce cell-seeded scaffolds to form vasculature (b) In vivo ectopic prevascularization involves implantation of a cell-

Recent Advances in Stem Cell and Tissue Engineering http://dx.doi.org/10.5772/intechopen.75967 125

In another similar study by [24], BM-MSC cell sheet technology was compared to control cell complex. The authors reported that BM-MSC cell sheet resulted into significant expressed levels of growth factors crucial to bone development like vascular endothelial growth factor and PDGF.In another innovative study of stem cell application in tissue engineering, Ren et al. fabricated

**Figure 1.** Showing in vivo and in vitro stem cell application in engineered tissue (a) In vitro prevascularization methods induce cell-seeded scaffolds to form vasculature (b) In vivo ectopic prevascularization involves implantation of a cellseeded scaffold into a highly vascularized bed. Adapted from [26] with copyright permission.
