De Novo Bone Formation by Adult Adipose-Derived Stem Cells/Alginate/Collagen Matrix in Prefabricated Vascularized Capsules in Rats: Application to Free Tissue Transfer

Bony defects of the extremities and the mandible secondary to trauma, tumor resection, or congenital deformity present significant morbidity for the patient, cost to society, and a challenging problem for the reconstructive surgeon. Current practices are limited by the size of the defect that can be repaired, poor viability/functionality post transplant, and morbidity at the donor-tissue site. An engineered tissue composed of osteoblast progenitors, a biocompatible scaffold, and functional microvascular network could eliminate most, if not all, of these complications. Initial results of this study demonstrate possible de novo bone formation from adipose-derived stem cells (ADSC) in an alginate/collagen matrix that has been co-implanted with bone fragments.

Subcutaneous fibrovascular capsules were created in the inguinal region of adult male Lewis rats. ADSCs obtained from male Lewis rats were suspended in a femoral bone fragment. X-ray images of the constructs were obtained once a week for 6–10 weeks to monitor changes in bone density. At the end of each time point, the constructs were removed and histological analysis (H&E) was performed to identify bone formation.

Radiographic analysis of the composite bone constructs by Faxitron demonstrated an increase in bone density over time. On histological examination, the ADSCs were viable and there seemed to be focal areas of de nova bone formation originating from the alginate/collagen matrix, especially near regions with bone marrow. The bone constructs were isolated on their vascular pedicle.

Both radiographic and histologic analysis of the composite bone constructs suggest that there is some de novo bone formation by ADSCs in the prefabricated vascularized capsules. The osteoconductive environment provided by the alginate/collagen matrix and the osteoeinductive factors provided from the bone marrow facilitated bone formation by implanted ADSCs. This provides the ground work for free tissue transfer of the tissue-engineered bone.