Nanoindentation measurements of viscoelastic material properties are sensitive to preparation techniques

This study tests the hypothesis that bone's tissue level elastic and viscoelastic mechanical properties are altered by dehydration and that rehydration can be used to recover changes to bone's mechanical properties. When samples were exposed to short periods of dehydration(24 hours) during sample preparation trabecular bone elastic modulus increased 36%(p<0.05) and tan δ decreased 33%(p<0.05). However, following rehydration both elastic modulus and tan δ were restored such that there were no differences between rehydrated samples and fresh controls. Similar results were found in cortical bone. When samples were exposed to long periods of dehydration(30 days) in sample preparation cortical bone elastic modulus increased 28%(p<0.05) and tan δ decreased 30%(p<0.05). Following rehydration, elastic modulus increased such that there was no difference between rehydrated and fresh controls. However, while tan δ increased following rehydration(12%, p<0.05), it was significantly lower than fresh controls (21%, p<0.05). Interestingly, cortical bone exposed to long term dehydration recovered tan δ such that there were no differences between rehydrated samples and fresh controls. Viscoelastic material properties most strongly reflect the mechanical contributions of collagen; therefore, one possible explanation could be that long term dehydration alters collagen organization, potentially through cross-linking.