A New Viscoelastic Model for Preconditioning in Ligaments and Tendons

In this paper, a new viscoelastic model is presented to describe the elastic and viscoelastic behaviors of ligaments and tendons during the preconditioning process. The model is formulated by accounting for the mechanical contribution of the main structures of ligaments and tendons, i. e., the collagen fibers, the proteoglycan-rich matrix and the coupling between the collagen fibers and the matrix. The coupling between the collagen fibers and the matrix is assumed to behave as the links binding the collagen fibers and the matrix together. According to the previous studies, the friction loss in ligaments and tendons plays a significant role on the stress softening and the decreasing of the hysteresis during preconditioning. Therefore, in this work, the links are assumed to gradually break during preconditioning and there will be no links breaking when the preconditioning is completed. Finally, the viscoelastic model can easily describe the stress softening and the decreasing of the hysteresis during preconditioning process. We believe that our model can provide a simple way to interpret the physical mechanism during the preconditioning process in ligaments and tendons.