Role of storage on changes in the mechanical properties of tendon and self-assembled collagen fibers.

Fibrous collagen networks are the major elements that provide mechanical integrity to tissues; they are composed of fiber forming collagens in combination with proteoglycans (PGs). Using uniaxial tensile tests we have studied the viscoelastic mechanical properties of rat tail tendon (RTT) fibers and self-assembled collagen fibers that were stored at 22 degrees C and 1 atm of pressure. Our results indicate that storage of RTT and self-assembled type I collagen fibers results in increased elastic and viscous components of the stress-strain behavior consistent with the hypothesis that storage causes the introduction of crosslinks. Analysis of the elastic and viscous mechanical data suggests that the elastic constant of the collagen molecule in RTT is about 7.7 GPa. Measurement of the viscous component of the stress-strain curves for RTTs and self-assembled collagen fibers suggests that PGs may increase the viscous component and effectively increase the collagen fibril length.