Mechanical Surface Testing of Bone Using Nanoindentation

Bone regeneration is a huge challenge in the field of Orthopedic Medicine. Present techniques for the treatment of massive bone loss are fundamentally dependent on artificial prostheses. Prostheses cannot be used for every case due to the limitation of movement and biocompatibility issues. Similarly, after long term use, the prosthesis can fail and result in the loss of function and possibly morbidity.

Nanoindentation AnalysisNew nanoscale analysis performed on bones and other mineralized biological materials open a new window into the intricate details of mechanical behavior at very small scales. Micro and macroscopic analysis, which yield averaged quantities over larger length scales, may not be sensitive enough to identify the underlying differences between two similar samples. Hence, nanoscale studies are desirable for the resolved characterization of these complex materials. Furthermore, nanoscale methodologies are beneficial when the volume of material available is too small for larger scale analyses, for instance with tissue engineered bone formation in rat models and critical-sized defects. The accuracy of biomechanical properties reduced using traditional engineering beam theory applied to whole bone bending analysis on mouse bone has also been questioned.

Nanoindentation analysis focuses on differences between trabecular and cortical bone, time dependent plasticity, anisotropy, variations as a function of distance from the osteonal center through the femoral cortex, viscoelasticity and varations due to mineral content.

So as to assess the role of intrinsic bone tissue quality in bone strength, a nanoindentation test was conducted at the level of the vertebral cortex of adult rats after a number of hormonal and dietary manipulations known to significantly impact bone strength of an intact skeletal piece.

The nanoindentation method evaluates both elasticity and hardness of wet and dry bone tissue with a high spatial resolution. Nanoindentation has also been proved to be a reliable technique to evaluate the intrinsic mechanical properties of single bone structural units (BSU). The local elastic properties of bone structural units were found to differ greatly among individuals, the type of bone (osteonal, interstitial, and trabecular), anatomical locations and trabecular orientation.

The results of the current research reveal that besides microarchitecture and geometry, intrinsic bone tissue property is a key determinant of the mechanical competence of rat vertebrae after low protein intake and dietary OVX treatment.

Figure 1. Force-displacement curve of a nanoindentation test: loading (1), holding (2), unloading (3) of an indenter tip. The third part leads to elastic recovery of the material and its initial slope is used to derive the elastic indentation modulus. The hysteresis represents the dissipated energy.

Nanoindentation signifies a test of the fundamental mechanical properties of bone tissue. This method obtains force displacement data of a pyramidal diamond indenter that is pressed into a material. The resulting curve comprising of three parts is shown in Figure 1. In part 1, the indenter tip is loaded onto the sample that leads to a complex combination of elastic and post yield deformation.

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This information has been sourced, reviewed and adapted from materials provided by Anton Paar GmbH.

For more information on this source, please visit Anton Paar GmbH.