Chondrocyte response to tensile and compressive cyclic loading modalities

There is very little data addressing cartilage response to tensile forces, and no literature attempts to correlate compressive with tensile modalities. Our hypothesis was that the cyclic compression and tension modulate chondrocyte matrix proteoglycan synthetic response differently. Porcine chondrocytes cultured to confluence on a flexible membrane were subjected to cyclic compression (Group A: 13 KPa at 1 Hz) or tension (Group C: 10% strain at 1 Hz) for 16 or 32 h; while controls not subjected to any force were kept (Group B). The chondrocytes were then stained with alcian blue and stained areas quantified with confocal microscopy and image processing software. Two-factor ANOVA with post-hoc tests (Scheffe and Bonferroni) statistical analysis were used. Proteoglycan staining covered 46% (range 28%-61%) and 39% (range 26%-49%) of the surface area following 32 and 16 h of compression respectively, 23% (range 15%-49%) for control, and 19% (range 10%-29%) and 16% (range 9%-25%) following 16 and 32 h tension respectively. Proteoglycan content following all compressions was significantly greater than with cyclic tension or control (p < 0.0001). Our data demonstrate that chondrocytes cultured in vitro respond to compression distinctly different from tension and that it is highly sensitive to mechanical loading, with rapid adaptation to its mechanical environment. These results imply that cartilage grown in culture, with the intention of transplantation, may structurally benefit from an environment of cyclic loading at higher frequencies.