A combined atomic force microscopy and nanoindentation technique to investigate the elastic properties of bone structural units.

To our knowledge, this study applied for the first time a recently developed combination of atomic force microscopy (AFM) and nanoindentation on trabecular and compact bone tissue. The major aim was to check the advantage of the available AFM-mode over the conventionally used optical microscope. First, we investigated if removal of the water content helped to prevent enzymatic degradation of the bone tissue and preserve its mechanical properties during a week. After the positive issue of this test, we quantified the intrinsic mechanical properties of single bone structural units (BSU). Bone specimens were obtained from the femoral neck of an 86 year old female. Four BSU were randomly selected and tested each with 24 indents of 5 mN maximum force. The available AFM mode proved to be a very useful tool for surface characterization and precise selection of the indentation area. The elastic modulus ranged from 18 -/+ 1.7 GPa for a BSU of compact bone to 22.5 -/+ 3.1 GPa for a BSU of trabecular bone. Hardness showed values between 0.6 -/+ 0.11 GPa for compact bone and 1.1 -/+ 0.17 GPa for trabecular bone. The results suggest that the micromechanics of bone tissue may also be described as an assembly of distinct structural units with rather homogeneous material properties.