Impact of microstructural alterations to collagen networks on their mechanical behavior: a fiber in silico study of the articular cartilage surface

Background The collagen fibril network is a primary structural component of articular cartilage, ensuring its mechanical integrity; however, during osteoarthritis, this network undergoes pronounced structural changes. Hence, this in silico study investigates the non-linear mechanical behavior of collagen fibril networks representing the superficial zone of cartilage, examining normal and osteoarthritic conditions. Methods A previously validated in silico multiscale three-dimensional fiber network model has been extended by incorporating fibril interconnections (crosslinks) to represent the collagen network. This was first analyzed under normal conditions, followed by systematic modifications of key parameters—fibril Young’s modulus, crosslink density, and fibril orientation—to simulate degenerative microstructural changes characteristic of osteoarthritic cartilage in the superficial zone. Subsequently, computational transverse tensile tests, with uniaxial tension applied perpendicular to the preferential fibril orientation, were conducted to evaluate network integrity. These simulations predicted macroscopic mechanical responses, including energy and stress distributions in fibrils and crosslinks, providing insight into the transverse mechanical behavior of the collagen network under normal and pathological conditions. Results In the normal configuration, fibril interconnections appear to contribute to a more linear macroscopic mechanical response. Axial and bending energies are comparable in fibrils, and a limited set of fibrils and crosslinks act as stress concentrators. For degenerated configurations, stresses and energies increase significantly when fibrils are close to randomly oriented. Moreover, a case of mechanical compensation is found, where reduced interconnectivity does not decrease network stiffness after loading. Conclusions The proposed framework provides a virtual platform for investigating the mechanical behavior of normal and degenerated articular cartilage based on collagen microstructure. This may be combined with microstructural information from medical imaging to enable quantitative in silico explorations of how collagen network alterations influence tissue-scale mechanics.