A bottom-up approach to model collagen fiber damage and failure in soft biological tissues

Understanding the damage and failure of load-carrying soft biological tissue is critical in the effectual treatment of injury and disease. The difficulty in experimentally identifying the intrinsic mechanisms by which damage initiates and accumulates, and how this ultimately leads to tissue rupture, has motivated the constitutive modeling of soft tissue failure. We present an extension of our previous microstructural continuum model (Miller and Gasser, 2021) that includes proteoglycan mediated collagen fibril sliding towards capturing the non-linear time dependent properties of collagenous tissue. We now additionally incorporate an interfibrillar failure (fibril pull-out) mechanism and showcase the resulting damage induced mechanical behavior across several length scales. Importantly, a bottom-up approach is further demonstrated, whereby the microstructural model is employed in a single-element representation of the modes of fracture. A qualitative description of soft tissue rupture is accordingly attained, to which an appropriate cohesive zone model for the equivalent fracture surface is then calibrated. In doing so, a surface-based discontinuous characterization of failure is directly derived from the upscaling of irreversible and dissipative damage mechanisms from the microscale.