Measuring the dynamic mechanical response of hydrated mouse bone by nanoindentation

Abstract

This study demonstrates a novel approach to characterizing hydrated bone’s viscoelastic behavior at the lamellar length scales using dynamic indentation techniques. We studied the submicron-level viscoelastic response of bone tissue from two different inbred mouse strains, A/J and B6, with known differences in whole bone and tissue-level mechanical properties. Our results show that bone having a higher collagen content or a lower mineral-to-matrix ratio demonstrates a trend towards a larger viscoelastic response. When normalized for anatomical location relative to biological growth patterns in the antero-medial (AM) cortex, bone tissue from B6 femora, known to have a lower mineral-to-matrix ratio, is shown to exhibit a significantly higher viscoelastic response compared to A/J tissue. Newer bone regions with a higher collagen content (closer to the endosteal edge of the AM cortex) showed a trend towards a larger viscoelastic response. Our study demonstrates the feasibility of this technique to be used to study local composition-property relationships in bone. Further, this technique of viscoelastic nanoindentation mapping of the bone surface at these submicron length scales is shown to be highly advantageous in studying sub-surface features, such as porosity, of wet hydrated biological specimens, which are difficult to identify using other methods.

Mechanical Characterization of Mesoscale Interfaces Using Indentation Techniques

“…41,[51][52][53] Most importantly, it has been demonstrated that the use of spherical indenters has the potential to produce indentation stressstrain curves (not just values of modulus and hardness). Furthermore, because the spherical indenters produce significantly lower concentrations in the imposed stress and/or strain fields compared to the sharp indenters, it is possible to control the indentation depths to relatively small values and investigate the local material response at low levels of plastic deformation.…”

“…They have been largely applied thus far to a broad range of metals and alloys, with only a limited number of applications in non-metals, such as brushes of carbon-nanotubes 53 and bone. 51,52 These limited applications do provide strong evidence for improving the analyses of the raw data gathered in the indentation measurements and in the extraction of meaningful properties. As a specific example, in the studies on bone, it was demonstrated that it is possible to reliably measure the differences in the local indentation stress-strain curves over very short length scales (of the order of tens of microns) and different mouse strains (see Fig.…”

A study of human and bovine trabecular bones using nanoindentation and quantitative backscattered electron imaging

“…However, the choice of embedding medium introduces a second factor which is the potential alteration of the composition and the physicochemical status of bone tissue with which it is in contact (Bushby et al, 2004;Mittra et al, 2006), thus resulting in hardening of the tissue. Epoxy resin or polymethymetacrylate (PMMA) embedding of undecalcified bone samples is a technique widely used for nanoindentation studies (Bushby et al, 2004;Paietta et al, 2011;Pathak et al, 2011).…”

“…Most of the nanoindentation work to date on trabecular bone tissue has been performed on dehydrated and embedded specimens (Hengsberger et al, 2001;Mittra et al, 2006;Pathak et al, 2011;Rho et al, 1997;Wang et al, 2006;. Ethanol dehydration is a common technique used to prepare bone samples prior to embedding in resin.…”

“…In trabecular bone, only one previous study examined the effect of ethanol dehydration on tissue properties, measured using micro-indentation, and it showed that dehydration in ethanol increased Vickers hardness measurement by 15-20% (Dall'Ara et al, 2007). Recently, attention has been paid to the effect of the degree of dehydration (through air-drying and use of absolute ethanol) on the measured bone properties (Pathak et al, 2011;, Wolfram et al found differences of up to 30% between wet (immersed) and dry (air-dry with 42% relative humidity) protocols for indentation of vertebral trabecular bone. Despite the fact that dehydration is known to alter bone tissue properties, indentation testing of hydrated bone samples still remains a significant challenge.…”