To enhance preventative and diagnostic techniques for metabolic bone diseases like osteoporosis, the mechanical properties of the bone must first be determined and understood. This is conducted by exploring the mechanical properties of bone at a microstructure level. Nanoindentation provides a direct and accurate method for measuring the reduced modulus and hardness of bone. When comparing previous studies undertaken on human bone, it was found that considerations into the effects of loading functions and creep were not heavily investigated. Therefore the effects of load functions and creep were tested on the osteon of a human femur head affected by osteoporosis. The lamellae layers were also investigated, along with effects of time.
The maximum loading time was first investigated. Loads ranging from 500-5000µN were tested for various holding times; 2s, 5s and 10s. It was found that increased depths reduced the mechanical properties of the bone. The data for various maximum loads was relatively scattered for the reduced modulus, however a loading range of 2300µN to 3200µN provided the most consistent results.
Upon determining an appropriate maximum load, 2.5mN, the effect of creep was investigated by testing various holding times; 5s, 10s, 20s, 30s, 50s and 100s. As bone is a viscoelasticity material insufficient loading conditions can result in error due to this effect. Holding times of 30s or more were found to dissipate creep. The reduced moduli for different holding times were found to be within the same range. This suggests the osteonal bone tested had a minimal creep affect.
When testing the change in mechanical properties for increased distance of lamellae layers from the Haversian canal of osteons, it was found the reduced modulus and hardness decreased by 20% and 33% for distance factors of 20ìm away from the Haversian canal. The present testing results were compared to those taken 2 years ago on the osteonal bone of the same sample. It was found the reduced modulus and hardness increased by 17%-20% and 31%-33% respectively over a time period of 2 years. The environment of storage and dryness were assumed to be the major contributing factors.