关键词: 循环张应力, 加力时间, 髁突软骨, 成骨

Abstract: Objective    To establish an in vitro mechanical culture model of rat condylar chondrocytes and investigate the effects of different cyclic tensile stress magnitude and loading duration on osteogenic differentiation. Methods    The study was conducted in the laboratory of Zhejiang Chinese Medical University from June 2021 to December 2022. The condylar chondrocytes were isolated after the Sprague-Dawley（SD）rats were sacrificed and dissected under sterile conditions，and condylar chondrocytes were cultured and identified by type Ⅱ collagen immunofluorescence staining. The second-generation condylar chondrocytes cultured in vitro were used for application of cyclic tensile stress. For the experimental group，the conditions were set as follows：the applied force was a 5%，10%，and 15% deformation rate gradient，the duration gradient was 6 h，12 h，and 24 h，and the applied force frequency was 1 Hz. The control group was the cells without any tensile stress applied. The mRNA expression of Runt-related transcription factor 2（Runx2），osteocalcin（OC），and Osterix（Osx）in rat condylar chondrocytes was detected by real-time fluorescence quantitative PCR. Results    Immunofluorescence staining of type Ⅱ collagen showed that the condylar chondrocytes of the second generation were stained uniformly. In addition，the cells were extended well and arranged in order. Two-factor analysis of variance showed that the relative mRNA expression levels of OC，Osx，and Runx2 in condylar chondrocytes were all statistically different under different tensile stress and duration（P < 0.05），and there was a significant interaction effect between the tensile stress and duration（P < 0.05）. When the tensile stress was 15%，the relative mRNA expression level of OC，Osx and Runx2 in condylar chondrocytes at different duration in the experimental groups was lower than that in the control group. The relative mRNA expression level of Runx2 in condylar chondrocytes at different duration in the experimental groups had no statistical difference compared with the control group when the tensile stress was 5%. The relative mRNA expression levels of OC，Osx，and Runx2 in condylar chondrocytes were higher than those in the control group after 24 h when the tensile stress was 10%. Moreover，among the three experimental groups，when the tensile stress was 10%，the relative mRNA expression level of OC and Osx in condylar chondrocytes of all the experimental groups was the highest after 24 h，and the differences were statistically significant（P < 0.05）. Conclusion    Different cyclic tensile stress and different duration have different osteogenic effect on rat condylar chondrocytes. The osteogenic effect of condylar chondrocytes may be better under the 10% tensile stress for 24 h.

Key words: cyclic tensile stress, application duration, condylar cartilage, osteogenesis