## 3 Undifferentiated Cells (Stem Cells)
### Adult Stem Cells
#### 3.4.2.2 Applications in BTE  
The ease of availability, high yield of cell isolation, and excellent proliferation rate are considered the main reasons for the use of ASCs in bone regeneration [199]. It has been shown that one gram of adipose tissue yields about \(5\times 10^{3}\) stem cells, which is 500-fold greater than the number of cells obtained from one gram of bone marrow [200; 201; 202]. However, some studies report a lower osteogenic capacity of ASCs in comparison to BMSCs. As an illustration, [PERSON] et al. compared the osteogenic activity of ASCs versus BM-MSCs in vitro [203]. They cultured both stem cell types in osteogenic medium containing dexamethasone, \(\beta\)-glycerophosphate, and acid ascorbic. The results revealed that 82% and 92% of the BM-MSCs are positive cells for ALP staining after two and three weeks of culturing in the osteogenic medium, respectively. In the case of ASCs, these percentages were 28% and 45%, which confirms the higher osteogenic capacity of the BM-MSCs in comparison to ASCs.  
In vitro osteogenic differentiation of ASCs may be achieved after 14 days of culturing in a conditioned medium supplemented with 1 nM dexamethasone, 2 mM b-glycerolphosphate, and 50 IM ascorbate-2-phosphate [188; 204]. However, other approaches have also been documented as reliable methods for differentiating ASCs as osteoblastic-like cells (Figure 7). For example, [PERSON] et al. clarified that the combination of recombinant human BMP-2 and ASCs can result in an improvement in the osteogenic potential in vivo [205].  
Figure 6: A representative schematic of ASCs isolation from fat tissue after digestion, isolation of stromal vascular fraction (SVF), and plating of SVF. Reproduced with permission from Reference [198].  
The in vivo differentiation of juvenile and adult ASCs into osteogenic lineages was first reported by [PERSON] et al. [207]. They implanted the ASCs-seeded apatite-coated PLGA scaffolds in the critical-size defects of mice. The results of the implantation of samples after two, four, eight, and 12 weeks showed that the juvenile ASCs-seeded apatite-coated scaffolds could form new bone (25%, 80%, 70%, and 85% bone formation, respectively) at the damaged site, while less bone formation (30%, 55%, 50%, and 70% bone formation, respectively) was observed in the groups treated with the adult ASCs/scaffolds. Moreover, they evaluated the effect of apatite coating on the progression of the new bone formation. The role of the apatite coating in promoting the osteogenic capacity of the osteoblast-seeded constructs further confirms the influence of scaffold biomaterial on cell activity and fate. At the same time (2004), the first report on the clinical use of hASC-fibrin glue for treating an extensive craniofacial injury in a seven-year-old girl was published by [PERSON] et al. [208].  
Evaluating the potential tumorigenic feature of ASCs before taking any clinical experiments is a necessary step. According to the literature, there is significant controversy about the effect of ASCs on tumor growth since some studies state ASCs may favor the growth of tumor cells, while other studies contradict these results [209].