Biomechanical response of collagen fascicles to restressing after stress deprivation during culture

In vitro tissue culture experiments were performed to study the biomechanical response of collagen fascicles to restressing after exposure to non-loaded condition. Collagen fascicles of approximately 300 μm in diameter were aseptically dissected from rabbit patellar tendons. They were cultured under no-load condition for 1 week, and then under a static stress of approximately 1.2 MPa for the subsequent 1 or 2 weeks. After culture, their mechanical properties were determined with a micro-tensile tester, and were compared to those of fascicles cultured under no-load condition and non-cultured, control fascicles. Tangent modulus and tensile strength of the non-loaded fascicles were significantly lower than those of the control fascicles at 1 week and gradually decreased thereafter. However, the modulus and strength were increased by restressing. After 2-week restressing, both parameters were significantly greater than those of the time-matched, non-loaded fascicles, although these values were still significantly lower than those of the control fascicles. That is, the application of stress after exposure to non-loaded condition suppressed the deterioration of the biomechanical properties of fascicles, although it did not improve. These results indicate that a short period of stressing is not sufficient for cultured collagen fascicles to completely recover their mechanical properties, if they are once exposed to no-stress condition even for a short period of time. These are similar to previous results observed in tendons and ligaments inside the body.