Mechanical property determination of bone through nano- and microindentation testing and finite element simulation

Mechanical property determination of very small volumes has become increasingly important, particularly since materials at small length scales (nano-scale) may have mechanical properties that are significantly different from those at bulk length scales. In order to access the nano-scale regime, attempts have been made to combine methods utilizing the quantitative data analysis models of indentation with the high resolution of high-performance load transducer. Modern nanoindentation techniques typically use the measured depth of penetration of the indenter and the known geometry of the indenter to determine the mechanical properties of a material.;Age-related bone fractures impose a significant social and economic problem on our increasingly aging population. Understanding the underlying mechanisms of those fractures may help generate strategies for prevention and treatment. In addition, bone tissue adapts in response to local fluctuations in mechanical loading conditions. The advantages of the indentation technique allow bone tissue properties to be probed at both nano- and micro-scale levels. Recently, indentation methods have been applied to biological materials, including bone tissue.;In this work, a methodology using nano- and microindentation to identify bone mechanical properties has been developed. The indentation system used is the Hystron TriboIndenter™ with both low load and high load transducers. An experimental design technique was used to investigate the relationship between testing conditions and computed mechanical properties. Nanoindentation was also performed through a bone cross section beneath a large indent to obtain the relationship between mechanical properties and the distance from the deformed region. From these results, evidence for plasticity-induced changes in mechanical properties was obtained. A four-parameter finite element model was applied to simulate the viscoelastic/plastic behavior of bone under low load and high load test conditions, corresponding to indentation in the nano- and micro-scales, respectively. The four-parameter simulations further reflect evidence of the effects of damage induced by indentation in bone. Finally a damage plasticity model was also applied to simulate the indentation behavior of bone. It was shown that this model can be more effective in simulating the unloading behavior of an indent, compared to the four-parameter viscoelastic/plastic model. The results highlight the complex mechanical response of bone during nano- and microindentation testing.