Wired silk architectures provide a biomimetic ACL tissue engineering scaffold

Silk has been increasingly investigated as a scaffold for tissue-engineered anterior cruciate ligament (ACL) grafts, primarily due to a uniquely advantageous combination of biocompatibility and robust biomechanical strength in the short and middle terms. While previous studies have explored the biomechanical and biological effects of graft geometry, these studies have largely ignored the effects of repeated loading on long term biomechanical performance—an important consideration considering the relatively slow rate with which the silk scaffold is remodeled. In the present study, we utilized a tensile bioreactor to carry out cyclic loading tests on various silk ACL scaffold designs. Silk scaffolds were fabricated with three different architectures (wired, braided, and straight fibered). These were tested in static loading, low cyclic loading to 250 cycles, and high cyclic loading to 100,000 cycles. Different scaffold conditions including dry, wet, with cells, without seeded cells were tested and compared. The ultimate tensile strength (UTS), linear stiffness and construct elongation rate were used to compare the structural behavior of each graft architecture. Based upon this analysis, silk scaffolds with a wired structure exhibited biomechanical behavior most similar to the native human ACL. We thus conclude that the wired silk scaffold design we present provides a biofidelic mechanical basis for tissue engineering strategies for ACL reconstruction.