Osteogenic Potential and Histological Characteristics of Mesenchymal Stem Cell Sheet/Hydroxyapatite Constructs

We have developed a new cell transplantation technique, in which mesenchymal stem cells (MSCs) were cultured and lifted as a cell sheet structure. The sheet formed bone tissue after in vivo transplantation at a subcutaneous site, without the need for any scaffold. The sheet could also be transplanted with a scaffold, such as hydroxyapatite (HA). Transplantation of this sheet/HA construct resulted in extensive bone formation. The purpose of the present study was to analyze the spatial distribution and biological potential of the osteogenic sheet/HA constructs. Histological examination showed that the construct allowed bone formation inside the pores, as well as outside the HA at 2 weeks after transplantation. Interestingly, when two HAs were wrapped in one sheet, the bone on the outside of one HA could bond to the bone on the other HA, resulting in union of two HAs. Biochemical investigation showed that the sheet/HA constructs had higher osteogenic potential than previous methods, such as MSC/HA constructs. Our results indicate that this transplantation technique using MSC sheets has the potential to be a useful tool in bone tissue engineering.