Methods: Human periodontal ligament stem cells (PDLSCs), gingival mesenchymal stem cells (GMSCs), human bone marrow stem cells and hBMSCs as the positive control were isolated and cultured. The stem cells were encapsulated in alginate microbeads with sizes of about 2±0.1 mm with density of 1 ×106stem cell/ mL of alginate. Microbeads containing PDLSCs, GMSCs and human bone marrow mesenchymal stem cell (hBMMSCs) were further implanted subcutaneously for 5-month-old Beige nude mice. Also, encapsulated stem cells were used surgically in the mice calvarial defect model. 7 mm diameter defects were created and the biomaterials were placed inside each of the defects. After 8 weeks the animals were sacrificed and standard radiographic examination, x-ray micro-computer tomography (μCT), and histological analysis were utilized to observe the amounts of bone formation at 8 weeks post-implantation.
Results: Standard radiographs prior to sacrificing the animals, revealed extensive calcifications both subcutaneously and within the defects for the dental-derived stem cells and the positive control group. μCT results confirmed mineralization inside and around the implanted microbeads containing the immobilized stem cells. However, alginate microbeads without stem cells did not promote any significant mineralization after 8 weeks. No statistically significant difference was observed among the values for bone volume fraction (BV/TV) for hBMMSC, PDLSCs and GMSCs. However, the values for hBMMSC, PDLSCs encapsulated in alginate were higher that the values of GMSCs (p>0.05).
Conclusions: These findings of our in vivo study demonstrated for the first time that immobilization of PDLSCs and GMSCs in the alginate hydrogel microbeads provides a promising strategy for bone tissue engineering.