Variations in the individual thick lamellar properties within osteons by nanoindentation

The nanoindentation method was used to examine variations in the individual thick lamellar properties within completed secondary osteons as a function of distance from the osteonal center (haversian canal). In general, there is a decline in both elastic modulus and hardness from the center of the osteon outward. Because some of the osteons may have a different general trend than others, an analysis of covariance was also carried out. The overall analysis was highly significant for both elastic modulus and hardness. Also, osteon number was significant as a factor, indicating that there was some difference in the overall thick lamellar properties of the different osteons. An unpaired t-test showed statistically significant differences (p = 0.0005 and 0.0004, respectively) between thick lamellar properties obtained from most of the inner two osteonal lamellae (E = 20.8 +/- 1.3 GPa and H = 0.65 +/- 0.06 GPa) and those from outermost two osteonal lamellae (E = 18.8 +/- 1.0 GPa and H = 0.55 +/- 0.05 GPa). In general, lamellar properties from near to the center of the osteon were greater than those from the outermost osteonal lamella. The mechanical properties of osteons are also significantly lower than those of the interstitial bone (p < 0.0001). The ratio (E1/E2) of the elastic moduli of the outermost osteonal lamella (E1) (considered to be the soft part of the osteons) and that of interstitial bone (E2) was approximately 0.7. These results may have important implications for the mechanical contribution of individual osteons to bone biomechanics.