Living reactions of tissue-engineered bone derived from apatite-fiber scaffold in rat subcutaneous tissues

We synthesized apatite fibers (AFs) and fabricated a porous hydroxyapatite scaffold (apatite-fiber scaffold; AFS). A tissue-engineered bone involving a three-dimensional structure was constructed by placing AFS in a radial-flow bioreactor (RFB) to culture rat bone marrow mesenchymal stem cells (RBMCs). In this study, we examined whether the tissue-engineered bone derived from the AFS has osteogenic differentiation potential leading to bone-forming ability in vivo in the subcutaneous tissue where bone formation does not occur naturally due to the absence of osteoblasts. The reconstructed tissue-engineered bone was implanted subcutaneously in rat tissue for 4 weeks. The AFS alone was implanted as a control. After implantation, some histological evaluations, i.e., hematoxylin and eosin (HE), alkaline phosphatase (ALP) staining, and immunofluorescence staining for osteocalcin (OC), were performed for the harvested samples. In addition, quantitative evaluation was also performed to determine the ALP activity normalized for the DNA content of the harvested samples. The HE staining revealed that both AFSs (control) and implanted tissue-engineered bone (RFB-bone) were biocompatible, and did not induce inflammation or immunological rejection in vivo. The ALP activity in the RFB-bone was significantly higher than that in the control. Immunofluorescent staining showed the expression of OC in RFB-bone. Therefore, we conclude that the tissue-engineered bone derived from AFS may have the bone-forming ability in vivo in the absence of osteoblasts. These results may provide valuable insights into the design of tissue-engineered bone for clinical applications.