Low intensity pulsed ultrasound accelerates delayed healing process by reducing the time required for the completion of endochondral ossification in the aged mouse femur fracture model.

The aim of this study is to clarify the effect of low intensity pulsed ultrasound (LIPUS) on shortening of the fracture healing period and endochondral ossification during the fracture healing process. We first established a model of aging-related delayed union fractures consisting of aged mouse (C57BL/6J; 40 weeks old) with closed femur fractures. We compared the healing process of 40-week-old mice to the healing process of 8-week-old (young) mice using radiological and histological analysis. In aged mice, some cartilage formation was observed 10 days after the fracture; however, endochondral ossification and hard callus bridging were observed 21 and 28 days after the fracture, respectively, whereas cartilage remained in the callus on day 28, suggesting delayed endochondral ossification following bone remodeling. Meanwhile, in aged mice with LIPUS treatment, cartilage formation was similar to that in aged mice without LIPUS; however, hard callus bridging and bone remodeling were observed 21 and 28 days after fracture, respectively, suggesting that LIPUS shortened the healing period due to promotion of endochondral ossification. Immunohistochemical analysis showed marked expression of vascular endothelial growth factor and neovascularization in the fibrous tissue comprising the periosteum that surrounded the whole callus. A cell migration test involving primary cultured human endothelial cells also showed promotion of cell migration by LIPUS. These results suggested that endothelial cell migration and neovascularization, which were observed around fracture sites, played a part in the mechanism of promotion of endochondral ossification by LIPUS.

Influence of three-dimensional culture in a type II collagen sponge on primary cultured and dedifferentiated chondrocytes.

BACKGROUND: Once articular cartilage is destroyed, the intrinsic reparative ability is poor. Therefore, various techniques have been developed to repair articular defects. Many kinds of scaffolds have been used for cultured chondrocyte transplantation. In this study, we developed a sponge consisting of type II collagen. We investigated the influence of three-dimensional culture on the maintenance of the chondrocyte phenotype and on the redifferentiation of dedifferentiated chondrocytes. METHODS: Chondrocytes were isolated from the rib cartilage of rats and were cultured in plastic dishes for a week (P0). The cells were then dissociated with trypsin and subcultured for another 2 weeks (P1). Primary isolated chondrocytes were cultured in the type II collagen sponges for 3 weeks (S1). We compared the gene expression of S1 for chondrogenic markers with the expression of P0 and P1 by reverse transcription-polymerase chain reaction (RT-PCR). The cells were then dissociated with trypsin and subcultured for another 2 weeks (P1) and then another 6 weeks (P3). Cells of P1 were subsequently cultured in type II collagen sponges for 4 weeks (P1r). At each time point, gene expression of chondrogenic markers was examined by RT-PCR. RESULTS: Gene expression of COL2A1, COL10A1, and aggrecan in S1 was the same as in P0. Gene expression of COL10A1 and aggrecan in P1r was higher than in P1 and P3. Gene expression of COL1A1, COL2A1, and SOX9 in P1r was lower than in P1 and P3. Gene expression of ALP and osteocalcin in P1r was detected. CONCLUSIONS: These results show that culture in type II collagen sponges could maintain the chondrocyte phenotype; however, dedifferentiated chondrocytes differentiated to hypertrophic chondrocytes. These finding suggest that the complex of cells and scaffolds with primary cells was more useful than that with dedifferentiated chondrocytes in laboratory and clinical application.