NANOINDENTATION OF BONE - Nanoindentation with Biological Applications - page 210

bone yielded elastic modulus values (22.4 ± 1.2 GPa) that were 35%
greater that that of the transversely-tested bone.
Anisotropy is measureable in both mineral and organic phases of
bone. Equine cortical bone samples, experimentally manipulated from a
wet, baseline condition to produce five different states: wet, dehydrated
(in 100% ethanol), embedded (ethanol dehydration followed by PMMA
embedding), decalcified, and deproteinated, showed characteristic
anisotropic behavior in all but the wet state ( Table 7-3 ) . 93 With the
exception of nanoindentation in wet bone, the modulus was significantly
elevated in the longitudinal direction for all other conditions. Due to
difficulties in sample preparation and testing of wet bone (as previously
discussed in this chapter), subtle differences in the longitudinal versus
the transverse indentation moduli may have been difficult to discern.
That anisotropy was measureable even in PMMA-embedded decalcified
bone demonstrates that the organization of the organic matrix may
contribute to the overall behavior of bone in nanoindentation.

Table 7-3. Values [mean [SD], number n =] of plane strain modulus ( E ') in
GPa from nanoindentation on planes that lie transverse and longitudinal to the
long axis of the bone. Student's t-test between transverse and longitudinal
directions - results reported as not significantly different (N.S.), significant
(*), or highly significant (**). Data are from Bembey et al. (2005). 93
Condition E ' Transverse

(GPa)

E ' Longitudinal
(GPa)

Wet 11.7 (1.7), 326 11.8 (1.9), 68 (N.S.)

Ethanol Dehydrated 15.0 (2.2), 309 24.8 (2.2), 68 **

PMMA Embedded 19.4 (2.1), 283 25.8 (2.1), 74 **

Deproteinated (Embedded) 13.4 (1.0), 62 20.4 (2.2), 62 **

Decalcified (Embedded) 4.9 (0.3), 59 5.5 (0.3), 49 *

Values for modulus collected for specific anatomically referenced
surface orientations can be compared to anisotropic elastic constants. 56,120
Nanoindentation is a multiaxial test where the measured modulus is a
combination of moduli in all directions and is relatively insensitive to
anisotropy (perhaps another reason for the lack of difference in wet bone
samples). 93 The measured indentation elastic modulus will vary with