Dynamic nanomechanical behaviour of healthy and OI human cortical bone

Viscoelasticity of bone has been of interest for many years because this time-dependent mechanical property relates to the fracture risk of bone under dynamic loading. Several factors have been claimed to contribute to this property including the nature of different constituents of bone and their interactions, as well as moisture content. In the present study, intact normal human cortical bone was demineralised, and molecular structures were identified using infrared spectroscopy. Osteogenesis imperfecta (OI) human cortical bone was also selected for comparison because OI bone has severe defects in collagen molecules, while its mineral phase is almost identical to that of normal bone. The dynamic nanomechanical behaviours of the intact, demineralised and OI human cortical bone specimens were examined using dynamic nanoindentation. Loss tangent, tan delta, was considered as a measure of the degree of the viscoelastic response. Variable dynamic load tests show that the viscoelastic responses of all bone specimens increase with frequency. With demineralisation, bone specimens show greater viscoelastic response than intact specimens. OI bone shows similar viscoelastic response as normal bone. Results suggest that the viscoelasticity of bone is mostly attributable to the mineral phase. The present study adds to the understanding of the viscoelastic response of bone material. In addition, the dynamic mechanical properties of OI bone are firstly reported here.