Prediction of microdamage formation using a mineral-collagen composite model of bone

Abstract

Age-related changes in bone quality are mainly manifested in the reduced toughness. Since the postyield deformation of bone is realized through microdamage formation (e.g., microcracking and diffuse damage), it is necessary to understand the mechanism of microdamage formation in bone in order to elucidate underlying mechanisms of age-related bone fractures. In this study, a twodimensional shear lag model was developed to predict stress concentration fields around an initial crack in a mineral-collagen composite. In this model, non-linear elasticity was assumed for the collagen phase, and linear elasticity for the mineral. Based on the pattern of the stress concentration fields, the condition for microdamage formation was discussed. The results of our analyses indicate that: (1) an initial crack formed in mineral phase may cause stress concentration in the adjacent mineral layers; (2) the pattern of stress concentration fields depends not only on the spatial but also mechanical properties of the collagen and mineral phases; (3) the pattern of the stress concentration fields could determine either coalescence or scattering of nano cracks around the initial crack.

Failure of mineralized collagen fibrils: Modeling the role of collagen cross-linking

“…We present a mechanistic model for bone fibril deformation and failure including details of collagen deformation, collagen-mineral interaction and mineral fracture. Past related models (Akkus, 2005, Hellmich et al, 2004Fritsch and Hellmich, 2007;Ja¨ger and Fratzl, 2000;Kotha and Guzelsu, 2003;Wang and Qian, 2006;Arnoux et al, 2002;Ji and Gao, 2004) had considered collagen as a homogeneous continuum. Here an enhanced continuum model is employed allowing for sliding between collagen molecules, mineral-collagen interface debonding and mineral fracture.…”

“…In Kotha and Guzelsu (2003), a yield condition for the collagen phase was included. Wang and Qian (2006) showed that increased non-enzymatic glycation reduces the collagen nonlinearity and makes crack coalescence more likely by allowing stress concentrations to develop around existing cracks. In combination this would make the tissue more brittle, and accelerate fracture.…”

Collagen cross-links as a determinant of bone quality: a possible explanation for bone fragility in aging, osteoporosis, and diabetes mellitus

“…In vivo studies from human and animal specimens, however, demonstrate that AGEs crosslinks are a determinant of bone strength, particularly postyield properties and toughness [66,68,78,98,122]. Such deteriorated bone mechanical properties induced by cross-link alteration has been shown to correlate with deformation and damage of bone [123] and microdamage accumulation [76]. There is a limitation in these studies as almost all studies employed Pen content as a surrogate marker of AGEs formation.…”

Modelling of bone fracture and strength at different length scales: a review

“…Wang & Qian [122] also used a shear-lag model of a mineral-collagen composite to predict stress concentrations around the initial crack to identify the mechanisms of microdamage formation in bone. The focus of their study was on age-related bone fracture mechanisms.…”