The effect of intermittent static biaxial tensile strains on tissue engineered cartilage

Mechanical stimulation of engineered cartilage constructs is a commonly applied method used to accelerate tissue formation and improve the mechanical properties of the developed tissue. While the effects of compression and shear have been widely studied, the effect of tension has received relatively little attention. As articular cartilage in vivo is subjected to a degree of static tension (pre-tension) even in the absence of externally applied loads, the purpose of this study was to investigate the effect of intermittent static biaxial tensile strains (BTS) on chondrocyte metabolism and resultant tissue formation. Using a custom-design loading fixture to apply BTS, the optimal conditions for stimulating extracellular matrix synthesis were under average magnitudes of 3.8% radial and 2.1% circumferential tensile strains for 30 min. Tissue constructs subjected to tensile strain stimulation 3 times/week for a period of 4 weeks displayed increased thickness (35 +/- 18%) and proteoglycan content (22 +/- 7%) without an associated change in mechanical properties. In contrast, constructs stimulated daily over the same time period exhibited negligible effects in terms of ECM accumulation suggesting that the frequency of stimulation needs to be precisely controlled. The results of this study demonstrate that while tension can be used as potential biomechanical stimulus to improve tissue formation, further optimization of this process needs to be conducted to improve ECM accumulation and tissue mechanical properties after long-term exposure to tensile stimuli.