The effect of fibrillar degradation on the mechanics of articular cartilage: a computational model

摘要

The pathogenesis and pathophysiological underpinnings of cartilage degradation are not well understood. Either mechanically or enzymatically mediated degeneration at the fibril level can lead to acute focal injuries that will, overtime, cause significant cartilage degradation. Understanding the relationship between external loading and the basic molecular structure of cartilage requires establishing a connection between the fibril-level defects and its aggregate effect on cartilage. In this work, we provide a multiscale constitutive model of cartilage to elucidate the effect of two plausible fibril degradation mechanisms on the aggregate tissue: tropocollagen crosslink failure () and a generalized surface degradation (). Using our model, the mechanics of aggregate tissue shows differed yield stress and post-yield behavior after crosslink failure and surface degradation compared to intact cartilage, and the tissue-level aggregate behaviors are different from the fibrillar behaviors observed in the molecular dynamics simulations. We also compared the effect of fibrillar defects in terms of crosslink failure and surface degradation in different layers of cartilage within the macroscale tissue construct during a simulated nanoindentation test. Although the mechanical properties of cartilage tissue were largely contingent upon the mechanical properties of the fibril, the macroscale mechanics of cartilage tissue showed similar to 10% variation in yield strain (tissue yield strain: similar to 27 to similar to 37%) compared to fibrillar yield strain (fibrillar yield strain: similar to 16 to similar to 26%) for crosslink failure and similar to 7% difference for the surface degradation (yield strain variations at the tissue: similar to 30 to similar to 37% and fibril: similar to 24 to similar to 26%) at the superficial layer. The yield strain was further delayed in middle layers at least up to 30% irrespective of the failure mechanisms. The cartilage tissue appeared to withst