Investigation for Effects of Cyclical Dynamic Compression on Matrix Metabolite and Mechanical Properties of Chondrocytes Cultured in Alginate

Articular cartilage is suffered from high mechanical loads under normal physiological conditions and articular chondrocytes regulate the composition of peri-cellular matrix (PCM), in response to mechanical signals. This study aims to investigate influence of cyclical dynamic compression on matrix metabolite and mechanical properties of chondrocytes cultured in alginate. Two months old New Zealand white rabbits were sacrificed by air embolism. Chondrocytes were taken from knee joints under aseptic conditions and cultured in alginate. The suspension was gelled in a shape of disc in CaCl2 solution and processed for intermittent compression by using Flexcell-5000 compression system kept under an uncompressed condition as a control. The gene regulation of aggrecan (Agg), collagen alpha! (Col-2), matrix metallo-proteinases 13 (MMP-13) and collagen X (Col-10) were determined by reverse transcription polymerase chain reaction (RT-PCR) at 7th, 14th and 21st day post loading. The alteration in mechanical properties of chondrocytes induced by compression was evaluated using micropipette aspiration technique combined with a half-space model. A significant up-regulation was observed in gene expression of Agg and Col-2 on 7th day or MMP-13 and Col-10 on 14th day respectively after loading of compression. In response to compression, chondrocytes exhibited viscoelastic solid creep behavior. Young's modulus almost approximated to control group (0.65 +/- 0.42kPa). However, viscoelastic properties decreased gradually along with intermittent compression. Viscoelastic properties in experimental 21st day, including equilibrium modulus (E-infinity), the instantaneous modulus (E-0) and apparent viscosity (mu) were significantly lower than experimental 7th day and 14th day (P<0.001), no significant difference was found between experimental 7th day and 14th day (P>0.05). In conclusion, chondrocytes cultured in alginate are stable of mechanical properties and suitable to construct seed cell of tissue engineering, and can keep phenotype and mechanical properties.