  Healthy cartilage is a remarkable tissue, able to withstand tens of millions
of loading cycles with minimal damage. While much is known about the structural
origins of its compressive mechanics, how composition determines its mechanical
behavior in shear, a major mode of failure, is poorly understood. Through a
combination of microscale structure-function experiments and modeling, we
develop a rigidity percolation framework to explain the structural origins of
cartilage shear mechanics. This framework provides a new quantitative
understanding for how the known degradative events in osteoarthritis determine
the mechanical changes that are a hallmark of this disease. As such, this work
provides a road map for understanding disease progression and in combination
with non-invasive techniques such as MRI will enable more effective diagnosis
and treatment.
