Effect of mineral dissolution from bone specimens on the viscoelastic properties of cortical bone

Although physiological saline (0.15 M NaCl aqueous solution) has been used as a storage solution to prevent bone specimens from drying, there have been reports that Ca2+ ions dissolve from bone specimens during the storage in saline. In order to determine whether such storage has a marked effect on mechanical properties, the relaxation modulus of bovine cortical bone stored in physiological saline was compared with that stored in a buffer solution containing a sufficient amount of Ca2+ ions. After storage in saline, the modulus value of specimens was significantly reduced from that before storage. On the other hand, the modulus value of specimens soaked in the solution containing sufficient Ca2+ ions did not change after storage. The relaxation rate of a bone specimen stored in physiological saline was larger than that of a specimen stored in Ca2+-buffered saline solution and that of the control specimens. The results suggest that by the dissolution of Ca2+ ions from a bone specimen during storage in physiological saline, percolated paths of mineral phase and of reinforced matrix phase are disjoined, resulting in reduction in the elastic modulus and change in the viscoelastic properties of bone.