Biomaterials for Bone Regeneration

Evaluating the mechanical properties of biomaterials 299

fact, at each instant t the stress value can be determined from the tangent

modulus measured at the same instant. In particular, the tangent modulus

can either decrease or increase over time, depending on whether we are

moving in a hardening or softening section of the stress–strain curve. This

method has proven to be quite reliable in experiments on arti cial elasto-

mers, as well as biological tissue.

Figure 9.11 shows the frequency spectra of both the storage modulus and

loss factor of a rat liver, taken at different times. One can observe that the

spectra, while maintaining the same shape, change over time; in particular,

the storage modulus tends to decrease and the loss factor ...