A Multiscale Investigation of Fatigue Induced Damage Progression in Tendon

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Tendon is a load-bearing tissue that is loaded through millions of cycles over a lifespan. These intense cyclic loads can lead to injury. This study will lay the groundwork for understanding the complexities in deteriorating structural integrity of tendon due to repeated loading. Tendon is a biological material with hierarchical “building blocks” that span several length scales. Therefore, it is important to understand the mechanical behavior and degradation due to fatigue loading at each scale. This work will use experiments at multiple scales, computational modeling, and advances in multiscale simulations to reveal how structural damage of the tissue affects the micro-environment of the tendon cells responsible for the repair of the tissue. Uncovering the mechanisms underlying tendon’s remarkable resilience to repeated loading will also guide the design of next generation engineered soft materials. This project will include contributions from students from underrepresented groups, including undergraduate students, and will contribute to summer outreach programs.This work will probe multiscale tendon mechanics with a series of clearly defined objectives, namely: 1) characterizing microscale fatigue response and damage of collagen fibrils, 2) developing a macroscopic model for fatigue induced damage, and 3) identifying damage-induced multiscale structural alterations that modify the tenocyte micro-environment. The absence of basic understanding and predictive capabilities for fatigue induced multiscale damage progression in tendon limits the progress of other basic studies including cell mechanics, translational studies, and development of mechanistically informed therapeutics. There is still a substantial gap in understanding the hierarchical cascade of plasticity in tendon during cyclic loading and how it correlates with tendon damage. Starting from collagen fibril experiments and coarse-grained molecular dynamics simulations at the same scale, this work will develop macroscopic theories and models for tendon that will be able to capture the response to tensile fatigue loading including damage initiation and failure. To facilitate predictions at the continuum level, a finite element framework for damage and plasticity at finite deformation will be developed and the simulation results calibrated against macroscopic (tendon-level) experiments for fatigue loading. This work has the potential to provide mechanistic understanding for fatigue induced tendon damage, uncover how alterations to the tenocyte micro-environment drive healing, and provide predictive capabilities that will ultimately inform exercise based treatments to tendinopathy.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.