On-site SEM and nanomechanical properties of human OI bone

Abstract

Modulus mapping and on-site field emission-scanning electron microscopy (FE-SEM) nanoindentation are both applied for the first time on ‘undisturbed’ healthy human and osteogenesis imperfecta (OI) human cortical bones in this work. Modulus mapping reveals the elastic moduli of hydroxyapatite and collagen to be 189·9 and 2·4 GPa for the normal bone and 294·7 GPa and 2·9 GPa for the OI bone respectively. Modulus mapping also indicates a spatial variation in the elastic moduli consistent with the distribution of mineralized fibril and extrafibrillar mineral. The diameter of collagen fibers and the size of mineral crystals in OI are observed to be smaller, and the mineral crystal in OI is also observed to be less anisotropic than those from the normal bone. The median elastic moduli of the OI bone sample are greater than those of the normal bone. On-site FE-SEM nanoindentation reveals the existence of a highly mineralized inner ring with higher elastic moduli adjacent to the Haversian canal and that the elastic nanomechanical properties of interstitial lamellae are greater than those of osteonal lamellae. A periodic modulation in modulus corresponding to the width of a lamella is also observed in on-site FE-SEM nanoindentation.