Mechanical model for critical strain in mineralizing biological tissues: application to bone formation in biomaterials

Design maps for scaffold constructs in bone regeneration

In this article, we propose a methodology for the rational design of scaffold constructs in bone-tissue engineering. The construct under investigation is a sandwich structure with an Intramedullary rod (IM), a Biological Sponge (BS) and an External sleeve (ES). The IM rod provides axial resistance, BS facilitates the growth of new bone and ES provides stability to the construct by resisting torsion and bending. We demonstrate that only select combinations of stiffness between IM and ES facilitate the growth of new bone. Perren's interfragmentary strain theory is employed to clearly identify regions favoring bone growth from those favoring the formation of cartilage. Finally, design maps are constructed that clearly identify the combinations facilitating timely bone growth.

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

Age-related changes in bone quality are mainly manifested in the reduced toughness. Since the post-yield 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 two-dimensional 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.